Duolingo (DUOL) 10-K29 Feb 242023 FY Annual reportFinancial data

Company Profile

Cover Page

Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2023	Feb. 27, 2024	Jun. 30, 2023
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-40653
Entity Registrant Name	Duolingo, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-3055872
Entity Address, Address Line One	5900 Penn Avenue
Entity Address, City or Town	Pittsburgh
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15206
City Area Code	(412)
Local Phone Number	567-6602
Title of 12(b) Security	Class A common stock, $0.0001 per share
Trading Symbol	DUOL
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 3,891,337,096
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement for its 2024 annual meeting of stockholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year ended December 31, 2023, are incorporated by reference into Part III of this Annual Report on Form 10-K.
Entity Central Index Key	0001562088
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		36,680,751
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		6,195,077

Audit Information

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2023
Audit Information [Abstract]
Auditor Name	Deloitte & Touche LLP
Auditor Location	New York, New York
Auditor Firm ID	34

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 747,610	$ 608,180
Accounts receivable	88,975	46,728
Deferred cost of revenues	53,931	35,041
Prepaid expenses and other current assets	7,282	7,234
Total current assets	897,798	697,183
Property and equipment, net	11,792	12,969
Goodwill	4,050	4,050
Intangible assets, net	15,995	8,497
Operating lease right-of-use assets	19,103	22,508
Deferred tax assets, net	766	633
Restricted cash	2,735	0
Other assets	1,718	1,507
Total assets	953,957	747,347
Current liabilities
Accounts payable	2,447	1,177
Deferred revenues	249,192	157,550
Income tax payable	792	1,069
Accrued expenses and other current liabilities	24,931	21,970
Total current liabilities	277,362	181,766
Long-term obligation under operating leases	21,094	23,503
Total liabilities	298,456	205,269
Commitments and contingencies (Note 10)
Stockholders’ equity
Class A common stock, $0.0001 par value; 2,000,000 shares authorized as of December 31, 2023 and December 31, 2022; 36,311 and 31,899 issued and outstanding at December 31, 2023 and December 31, 2022, respectively Class B common stock, $0.0001 par value; 30,000 shares authorized as of December 31, 2023 and December 31, 2022; 6,215 and 8,462 issued and outstanding at December 31, 2023 and December 31, 2022, respectively	4	4
Additional paid-in capital	869,918	772,562
Accumulated deficit	(214,421)	(230,488)
Total stockholders’ equity	655,501	542,078
Total liabilities and stockholders' equity	$ 953,957	$ 747,347

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares shares in Thousands	Dec. 31, 2023	Dec. 31, 2022
Common Class A
Common stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	2,000,000	2,000,000
Common stock, shares issued (in shares)	36,311	31,899
Common stock, shares outstanding (in shares)	36,311	31,899
Common Class B
Common stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	30,000	30,000
Common stock, shares issued (in shares)	6,215	8,462
Common stock, shares outstanding (in shares)	6,215	8,462

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Revenues	$ 531,109	$ 369,495	$ 250,772
Cost of revenues	142,105	99,431	69,186
Gross profit	389,004	270,064	181,586
Operating expenses:
Research and development	194,352	150,444	103,833
Sales and marketing	75,788	66,967	59,170
General and administrative	132,123	117,848	78,590
Total operating expenses	402,263	335,259	241,593
Loss from operations	(13,259)	(65,195)	(60,007)
Other income	590	131	318
Other expense	(645)	(807)	(288)
Other (expense) income, net	(55)	(676)	30
Loss before interest income and income taxes	(13,314)	(65,871)	(59,977)
Interest income	31,091	7,235	19
Income (loss) before income taxes	17,777	(58,636)	(59,958)
Provision for income taxes	1,710	938	177
Net income (loss)	16,067	(59,574)	(60,135)
Net comprehensive income (loss)	$ 16,067	$ (59,574)	$ (60,135)
Net income (loss) per share attributable to Class A and Class B common stockholders, basic (in usd per share)	$ 0.39	$ (1.51)	$ (2.57)
Net income (loss) per share attributable to Class A and Class B common stockholders, diluted (in usd per share)	$ 0.35	$ (1.51)	$ (2.57)

CONSOLIDATED STATEMENTS OF CONV

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Convertible preferred stock beginning balance (in shares) at Dec. 31, 2020	19,074
Convertible preferred stock beginning balance at Dec. 31, 2020	$ 182,609
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)	(19,074)
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	$ (182,609)
Convertible preferred stock ending balance (in shares) at Dec. 31, 2021	0
Convertible preferred stock ending balance at Dec. 31, 2021	$ 0
Beginning balance (in shares) at Dec. 31, 2020		12,794
Beginning balance at Dec. 31, 2020	(80,691)	$ 1	$ 30,087	$ (110,779)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Issuance of common stock in connection with initial public offering, net of underwriting discounts and issuance costs (in shares)		4,466
Issuance of common stock in connection with the initial public offering, net of underwriting discounts and issuance costs	426,192	$ 1	426,191
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)		19,074
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	182,609	$ 2	182,607
Stock-based compensation expense	40,804		40,804
Stock options exercised (in shares)		1,882
Stock options exercised	12,480		12,480
Common stock repurchased and retired (in shares)		(23)
Common stock repurchased and retired	(868)		(868)
Options repurchased	(7,335)
Release of restricted stock units (in shares)		79
Net income (loss)	(60,135)			(60,135)
Ending balance (in shares) at Dec. 31, 2021		38,272
Ending balance at Dec. 31, 2021	513,056	$ 4	683,966	(170,914)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Stock-based compensation expense	73,820		73,820
Stock options exercised (in shares)		1,739
Stock options exercised	14,776		14,776
Release of restricted stock units (in shares)		350
Net income (loss)	(59,574)			(59,574)
Ending balance (in shares) at Dec. 31, 2022		40,361
Ending balance at Dec. 31, 2022	542,078	$ 4	772,562	(230,488)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Stock-based compensation expense	95,221		95,221
Release of performance stock units (in shares)		180
Taxes paid related to net-share settlements of share-based compensation awards ( in shares)		(84)
Taxes paid related to net-share settlements of share-based compensation awards	$ (11,482)		(11,482)
Stock options exercised (in shares)	1,396	1,396
Stock options exercised	$ 13,617		13,617
Release of restricted stock units (in shares)		673
Net income (loss)	16,067			16,067
Ending balance (in shares) at Dec. 31, 2023		42,526
Ending balance at Dec. 31, 2023	$ 655,501	$ 4	$ 869,918	$ (214,421)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income (loss)	$ 16,067	$ (59,574)	$ (60,135)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	7,095	4,870	2,726
Stock-based compensation expense	95,221	73,820	40,804
Gain on sale of capitalized software	(100)	0	0
Loss on disposal of leasehold improvements	433	0	0
Changes in assets and liabilities:
Deferred revenue	91,642	59,283	43,475
Accounts receivable	(42,247)	(13,565)	(12,713)
Deferred cost of revenues	(18,890)	(10,822)	(10,634)
Prepaid expenses and other current assets	(48)	(1,415)	(4,048)
Accounts payable	1,261	(6,655)	5,622
Accrued expenses and other current liabilities	3,444	8,720	3,708
Noncurrent assets and liabilities	(264)	(1,006)	365
Net cash provided by operating activities	153,614	53,656	9,170
Cash flows from investing activities:
Capitalized software expense and purchases of intangible assets	(10,493)	(4,562)	(2,620)
Purchase of property and equipment	(3,191)	(5,562)	(3,586)
Proceeds from sale of capitalized software	100	0	0
Acquisition, net of $0 cash acquired	0	(4,050)	0
Net cash used for investing activities	(13,584)	(14,174)	(6,206)
Cash flows from financing activities:
Issuance of common stock in connection with the initial public offering, net of underwriting discounts and issuance costs	0	0	426,191
Net proceeds from issuance of convertible preferred stock	0	0	0
Proceeds from exercise of stock options	13,617	14,776	12,480
Repurchases of stock options	0	0	(7,335)
Repurchase of common stock	0	0	(868)
Taxes paid related to net-share settlement of share-based compensation awards	(11,482)	0	0
Net cash provided by financing activities	2,135	14,776	430,468
Net increase in cash, cash equivalents and restricted cash	142,165	54,258	433,432
Cash, cash equivalents and restricted cash - Beginning of period	608,180	553,922	120,490
Cash, cash equivalents and restricted cash - End of period	750,345	608,180	553,922
Supplemental disclosure of cash flow information:
Cash paid for interest	0	0	0
Cash paid for income taxes	2,320	615	132
Supplemental disclosure of noncash operating activities:
Implementation costs for cloud computing included in Current liabilities	0	0	64
Supplemental disclosure of noncash investing activities:
Capitalized software and purchases of intangible assets included in Current liabilities	0	1,121	342
Property and equipment included in Current liabilities	165	166	230
Landlord incentive included in Prepaid expenses and other current assets	0	2,148	0
Right of use assets disposed or adjusted, modifying operating leases liabilities	2,024	0	0
Deferred offering costs included in accrued expenses	$ 0	$ 0	$ 0

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Statement of Cash Flows [Abstract]
Cash acquired during acquisition	$ 0

DESCRIPTION OF THE BUSINESS AND

DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION	12 Months Ended
DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION Duolingo, Inc. (the “Company” or “Duolingo”) was formed on August 18, 2011, and the Duolingo App was launched to the general public on June 19, 2012. The Company’s headquarters are located in Pittsburgh, Pennsylvania. On July 30, 2021, Duolingo completed its Initial Public Offering (“IPO”) of 5,872 shares of its Class A common stock at a price to the public of $102.00 per share, 4,466 of which were sold by the Company and 1,406 of which were sold by certain selling stockholders, which includes the exercise in full by the underwriters of their option to purchase from the Company an additional 766 shares of the Company’s Class A common stock. The gross proceeds to the Company from the IPO were $455,532, before deducting underwriting discounts and commissions and offering expenses payable by the Company. The Company did not receive any proceeds from the sale of shares of Class A common stock in the offering by the selling stockholders. Immediately prior to the completion of the IPO, all convertible preferred stock outstanding, totaling approximately 19,074 shares, was automatically converted into an equivalent number of shares of Class B common stock on a one-to-one basis and their carrying value of $182,609 was reclassified to additional paid-in capital within stockholders’ equity. Additionally, on July 15, 2021, 6,930 shares held by our founders were exchanged from Class A common stock into Class B common stock. Duolingo is a US-based mobile learning platform, as well as a digital English language proficiency assessment exam. The Company has a freemium business model: the app and the website are accessible free of charge, although Duolingo also offers premium services for a subscription fee. As of the date of this filing, Duolingo offers courses in over 40 different languages, including Spanish, English, French, German, Italian, Portuguese, Japanese and Chinese. We have locations in the U.S., China and Germany. Principles of Consolidation —The Consolidated Financial Statements include the accounts of the Company and subsidiaries over which the Company has control. All intercompany transactions and balances have been eliminated. Basis of Presentation —The accompanying Consolidated Financial Statements have been prepared in accordance with generally accepted accounting principles in the U.S. (“GAAP”) from the Company’s accounting records and reflect the consolidated financial position and results of operations for the years ended December 31, 2023, 2022, and 2021. Unless otherwise specified, all dollar amounts (other than per share amounts) are referred to in thousands.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Dec. 31, 2023
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Accounting Principles —The Consolidated Financial Statements and accompanying notes are prepared in accordance with GAAP. Use of Estimates— The preparation of Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying notes. Significant estimates and assumptions reflected in the Consolidated Financial Statements include, but are not limited to, useful lives of property and equipment, valuation of deferred tax assets and liabilities, stock-based compensation, common stock valuation, operating lease right-of-use assets and liabilities, capitalization of internally developed software and associated useful lives and contingent liabilities. Actual results may differ materially from such estimates. Management believes that the estimates, and judgments upon which they rely, are reasonable based upon information available to them at the time that these estimates and judgments are made. To the extent that there are material differences between these estimates and actual results, the Company’s Consolidated Financial Statements will be affected. Revenue Recognition— The Company has four predominant sources of revenue; time-based subscriptions, in-app advertising placement by third parties, the Duolingo English Test, and In-App Purchases. See Footnote 4 for further discussion. Deferred Revenues— Revenue is recognized over the life of the subscription, or in the case of Duolingo English Test, revenue is recognized when the test is proctored. The Company classifies deferred revenue as a short-term liability on the consolidated balance sheets as the longest subscription plan is for twelve months, and Duolingo English Test purchases must be taken within 21 days. Cost of Revenues— Cost of revenue predominantly consists of third-party payment processing fees charged by various distribution channel and hosting fees. To a much lesser extent, includes wages and stock-based compensation for certain employees in the capacity of customer support, amortization of revenue generating capitalized software, and depreciation of certain property and equipment. Deferred Cost of Revenues— Deferred cost of revenue includes third-party payment processing fees amortized over the subscription terms in proportion to the revenue recognized. In situations where fees are charged for subscriptions that exceed one month, costs are deferred and recognized over the life of the subscription and are classified as a current asset. The Company classifies deferred cost of revenue as a short-term asset on the Company’s consolidated balance sheets as the longest subscription plan is for twelve months. Cash and Cash Equivalents— Cash consists primarily of cash on hand and bank deposits. Cash equivalents consist primarily of money market accounts with maturities of three months or less at the date of acquisition and are stated at cost, which approximates fair value. The Company maintains cash deposits with financial institutions that may exceed federally insured limits at times. The following table shows the breakout between cash and money market funds. December 31, December 31, Cash $ 50,373 $ 91,189 Money market funds 697,237 516,991 Total $ 747,610 $ 608,180 The Money market funds are considered Level 1 financial assets. Level 1 financial assets use inputs that are the unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Restricted Cash— Restricted cash consists of a collateralized letter of credit established in connection with a lease agreement for the Company’s Sub-Sublease in New York, which was signed in December 2023. Restricted cash is included in non-current assets for leases that expire in more than one year from the balance sheet date. Accounts Receivable —Accounts receivables are reported on the consolidated balance sheets at the outstanding principal amount adjusted for any allowance for credit losses and any charge offs. The Company provides an allowance for credit losses to reduce trade receivables to their estimated net realizable value equal to the amount that is expected to be collected. This allowance is estimated based on historical collection experience, the aging of receivables, specific current and expected future macro-economic and market conditions, and assessments of the current creditworthiness and economic status of customers. The Company considers a receivable delinquent if it is unpaid after the term of the related invoice has expired. Balances that are still outstanding after management has used reasonable collection efforts are written off. The Company reviews its allowance for credit losses on a quarterly basis. As of December 31, 2023 and 2022, the Company has not recorded a reserve given the Company’s lack of historical write offs. Property and Equipment —Property and equipment is stated at cost, less accumulated depreciation. Depreciation is computed on the straight-line method. Asset Class Estimated Useful Life Furniture, fixtures and equipment 4 to 6 years Leasehold improvements 5 to 7 years Leasehold improvements are amortized over the lesser of the life of the lease or the estimated useful life of the leasehold improvements. Costs related to maintenance and repairs that do not extend the assets’ useful life are expensed as incurred. Acquisition —The Company uses the acquisition method of accounting for business combination transactions, and, accordingly, recognizes the fair values of assets acquired and liabilities assumed in our Consolidated Financial Statements. Transaction costs related to the acquisition of the acquired company are expensed as incurred. The allocation of fair values may be subject to adjustment after the initial allocation for up to a one-year period as more information becomes available relative to the fair values as of the acquisition date. The Consolidated Financial Statements include the results of operations of any acquired company since the acquisition date. Goodwill —The Company recognizes the excess of the purchase price over the fair value of identifiable net assets acquired at the acquisition date as goodwill. Goodwill is not amortized but is reviewed for impairment annually and more frequently if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying value. The Company will review goodwill for impairment annually on October 1st of each fiscal year or whenever events or changes in circumstances indicate that an impairment may exist. The Company will first perform a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying value. If the reporting unit does not pass the qualitative assessment, then the reporting unit’s carrying value is compared to its fair value. If the fair value of the reporting unit is greater than the reporting unit’s carrying value, then the carrying value of the reporting unit is deemed to be recoverable. If the carrying value of the reporting unit is greater than the reporting unit’s fair value, goodwill is impaired and written down to the reporting unit’s fair value. Intangible Assets —The majority of the Company’s intangible assets is capitalized software, with minimal other intangible assets during the years ended December 31, 2023 and 2022. The Company develops software for internal use and capitalizes the software development costs incurred during the application development stage. Costs incurred prior to and after the application development stage are charged to expense. When the software is ready for its intended use, capitalization ceases and such costs are amortized on a straight-line basis over the estimated life, which is generally three years. Relatively minor upgrades, enhancements and maintenance to the platform are expensed as incurred. Income Taxes— The Company provides for income taxes in accordance with the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the carrying amounts of existing assets and liabilities for financial reporting and for income tax reporting. The deferred tax asset or liability represents the future tax return consequences of those difference, which will either be taxable or deductible when the assets and liabilities are recovered or settled. A valuation allowance is established for any deferred tax asset for which it is determined that it is more likely than not that some or all of the deferred tax assets will not be realized. The Company limits the deferred tax assets recognized related to certain officers’ compensation to amounts that it estimates will be deductible in future periods based upon Internal Revenue Code Section 162(m). The Company utilizes a two-step approach to recognizing and measuring uncertain tax positions accounted for in accordance with the asset and liability method. The first step is to evaluate the tax position for recognition by determining whether evidence indicates that it is more likely than not that a position will be sustained if examined by a taxing authority. The second step is to measure the tax benefit as the largest amount that is 50% likely of being realized upon settlement with a tax authority. There were no amounts recorded at December 31, 2023 and December 31, 2022 related to uncertain tax positions. Foreign Currency —The functional currency of the Company and its subsidiaries is the U.S. dollar. Transactions denominated in currencies other than the functional currency are translated into the functional currency at the exchange rates prevailing at the dates of the transaction. Monetary assets and liabilities denominated in foreign currencies are translated using the exchange rate prevailing at the balance sheet date. Non-monetary assets and liabilities are translated using the historical rate on the date of the transaction. All exchange gains or losses arising from translation of these foreign currency transactions are included in net loss for the year. The Company has not, to the date of these Consolidated Financial Statements, entered into derivative instruments to offset the impact of foreign currency fluctuations. Fair Value of Financial Instruments —The Company accounts for certain assets and liabilities at fair value in accordance with the accounting guidance applicable to fair value measurements and disclosures. The carrying values of cash, cash equivalents, accounts receivable, accounts payable, and accrued expenses are deemed to be reasonable estimates of their fair values because of their short-term nature. Research and Development Costs —Research and development expenses are incurred as the Company maintains and enhances its software and evaluates and develops other potential applications. Such expenses include compensation of engineering, product design and testing personnel, including stock-based compensation, materials, travel and direct costs associated with the design and required testing of our platform and depreciation of certain property and equipment. Sales and Marketing —Sales and marketing expenses are expensed as incurred and consists primarily of brand advertising, marketing, digital and social media spend, field marketing, travel, trade show sponsorships and events, conferences and other employee-related compensation, including stock-based compensation for personnel engaged in sales and marketing functions, amortization of non-revenue generating capitalized software used to promote Duolingo, and depreciation of certain property and equipment. Advertising costs were approximately $52,969, $48,111 and $42,964 for the years ended December 31, 2023, 2022 and 2021, respectively. General and Administrative —General and administrative expense primarily consists of employee-related compensation (including stock-based compensation) for management and administrative functions, including our finance and accounting, legal, and people teams. General and administrative expense also includes certain professional services fees, general corporate and director and officer insurance, facilities costs, and other general overhead costs that support our operations, and depreciation of certain property and equipment. Contributors— On March 10, 2021, the Company announced that it was ending its non-employee volunteer program, which began in 2013 to build and improve language courses. As part of this change, those contributors who participated in the program became eligible to receive a one-time award, up to an aggregate amount of approximately $4,220, including fees paid to process payments of approximately $526. The Company accounted for this under Financial Accounting Standards Board (“FASB”) Accounting Standards Codifications (“ASC”) 958-720, Not-For-Profit Entities - Other Expenses and ASC 720-25, Contributions Made , based on the nature of this contribution, which is an unconditional promise. This amount is included within Sales and marketing in the Consolidated Statements of Operations and Comprehensive Income (Loss). Concentration of Credit Risk —The Company’s concentration of credit risk relates to financial institutions holding the Company’s cash and cash equivalents and platforms with significant accounts receivable balances and revenue transactions. The Company maintains cash deposits with financial institutions that may exceed federally insured limits at times. Management believes that the financial institutions that hold the Company’s deposits are financially credit worthy and, accordingly, minimal credit risk exists with respect to those balances. The majority of our revenue comes through our subscriptions and advertising streams and payments are made to Duolingo through service providers. The top three, Apple, Google and Stripe accounted for 65.2%, 20.7% and 10.7% of total Accounts receivable as of December 31, 2023, respectively. The top two service providers, Apple and Google, accounted for 56.2% and 27.5% of total Accounts receivable as of December 31, 2022, respectively. Three service providers, Apple, Google, and Stripe processed 58.5%, 25.6%, and 12.1% of total Revenues for the year ended December 31, 2023, respectively. Two services providers, Apple and Google, processed 54.2% and 28.1% of total Revenues for the year ended December 31, 2022, respectively. Three service providers, Apple, Google and Stripe, processed 50.5%, 29.0%, and 10.1% of total Revenues for the year ended December 31, 2021, respectively. Stock-Based Compensation —The Company accounts for equity-based compensation using the fair value method as set forth in the ASC 718, Compensation—Stock Compensation , which requires the measurement and recognition of compensation expense for all stock-based payment awards based on estimated fair values. This method requires companies to estimate the fair value of stock-based compensation on the date of grant using an option pricing model. The Company estimates the fair value of each equity-based payment award on the date of grant using the Black-Scholes pricing model. The Black-Scholes model determines the fair value of equity-based payment awards based on the fair value of the underlying common stock on the date of grant and requires the use of estimates and assumptions, including the fair value of the Company’s common stock, exercise price of the stock option, expected volatility, expected life, risk-free interest rate and dividend rate. The Company estimates the expected volatility of its stock options by taking the average historical volatility of a group of comparable publicly traded companies over a period equal to the expected life of the options; it is not practical for the Company to estimate its own volatility due to the lack of historical prices. The expected term of the options is determined in accordance with existing equity agreements as the underlying options are assumed to be exercised upon the passage of time. The risk-free interest rate is the estimated average interest rate based on U.S. Treasury zero-coupon notes with terms consistent with the expected life of the awards. The expected dividend yield is zero as the Company does not anticipate paying any recurring cash dividends in the foreseeable future. The Company accounts for forfeitures as they occur. Restricted Stock Units (RSUs) The Company began to grant RSUs in November 2020. The fair value of RSUs is estimated based on the fair value of the Company’s common stock on the date of grant. Each RSU award granted prior to the IPO vests based upon the satisfaction, during the term of the RSUs, of two requirements: length of service and a liquidity event defined as a change in control or a qualified IPO. The service-based vesting condition for the majority of these awards is satisfied over four years. The liquidity-based vesting condition is satisfied upon the occurrence of a qualifying liquidity event. The Company measures and recognizes compensation expense for all stock-based awards based on the estimated fair value of the award. Prior to July 30, 2021, no stock-based compensation expense had been recognized for RSUs because the liquidity-based vesting condition had not been probable of being satisfied. Upon the IPO, the liquidity-based vesting condition was satisfied and $2,035 of stock-based compensation expense was recognized related to these awards during the year ended December 31, 2021. Of that amount, $1,332, $210 and $493 was included within Research and development, Sales and marketing and General and administrative, respectively, in the Consolidated Statements of Operations and Comprehensive Income (Loss). Performance-based RSUs In June 2021, the Company granted 1,800 (one million eight-hundred thousand) performance-based RSUs to the Company’s founders (“Founder Awards”). The Founder Awards are divided into ten equal tranches with each tranche becoming eligible to vest upon achievement of the specified stock-price hurdles. The Founder Awards vest upon the satisfaction of both a service-based condition and a performance-based condition and generally are settled one year after vesting. The service-based condition is satisfied as to 25% of the Founder Awards on each anniversary of the completion of the IPO, subject to the continuous service of the founders through the applicable date. The fair value of the Founder Awards is determined using a Monte Carlo simulation model. The associated stock-based compensation is recorded over the derived service period, using the accelerated attribution method. If the stock-price hurdles are met sooner than the requisite service period, the stock-based compensation expense will be adjusted to prospectively recognize the remaining expense over the remaining derived service period. Provided that the founders continue to provide services to us, stock-based compensation expense is recognized over the derived service period, regardless of whether the stock-price hurdles are achieved. The first and second tranches were met during the year ended December 31, 2021. The third and fourth tranches were met during the year ended December 31, 2023. The Company recognized $26,622, $30,997 and $16,463 of stock-based compensation expense related to these awards, during the years ended December 31, 2023, 2022 and 2021, respectively, which is included within General and administrative in the Consolidated Statements of Operations and Comprehensive Income (Loss). Contingencies —The Company records accruals for contingencies and legal proceedings expected to be incurred in connection with a loss contingency when it is probable that a liability has been incurred and the amount can be reasonably estimated. If a loss contingency is not probable, but is reasonably possible, or is probable but cannot be estimated, the nature of the contingent liability, together with an estimate of the range of possible loss, would be disclosed. Segment —The Company operates as a single operating segment. The chief operating decision maker of the Company is its Chief Executive Officer, who makes resource allocation decisions and assesses performance based on financial information presented on a consolidated basis, accompanied by disaggregated information of our revenue. Accordingly, the Company has determined that it has a single reportable segment and operating segment structure, and operates as one reporting unit. Leases —The Company accounts for leases in accordance with ASC 842, Leases , which requires virtually all leases, other than leases that meet the definition of a short-term lease, to be recorded on the balance sheet with a right-of-use (“ROU”) asset and corresponding lease liability. ROU assets are periodically reviewed for impairment whenever events or changes in circumstances arise. During the years ended December 31, 2023, 2022 and 2021, the Company incurred no impairment charges on ROU assets. On the lease commencement date, each lease is classified as either finance or operating, depending on certain criteria. The Company determined that it only has operating leases as none of the criteria for finance lease classification were met. Operating lease expense is recognized on a straight-line basis on the Consolidated Statements of Operations and Comprehensive Income (Loss) in General and administrative expenses. On the Consolidated Statements of Changes in Cash Flows, payments for operating leases, are included in operating activities. As an accounting policy election, the Company has elected to not separate lease and non-lease components for all asset classes and made an accounting policy election for short-term leases which does not require the capitalization of leases with terms of 12 months or less at lease commencement. The discount rate utilized in calculating the lease liability is the rate implicit in the lease, if known; otherwise, the incremental borrowing rate (“IBR”) for the expected lease term is used. The Company’s IBR approximates the rate the Company would have to pay, on a collateralized basis, to borrow an amount equal to the lease payments under similar terms. Impairment of long-lived assets— The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the estimated undiscounted future cash flows expected to result from the use and eventual disposition of an asset is less than the carrying amount of the asset, an impairment loss is recognized. Measurement of an impairment loss is based on the fair value of the asset. No assets were impaired during the years ended December 31, 2023, 2022 and 2021. Recently Issued Pronouncements Not Yet Adopted There are no recently issued accounting pronouncements that the Company has not yet adopted that they believe are applicable or would have a material impact on the financial statements of the Company. In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-07, Segment Reporting (Topic 280), which improves reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. The standard is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The Company does not expect the adoption of the new guidance will have a material impact on the Company’s consolidated financial statements and related disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740), which includes improvements to income tax disclosures. The standard is effective for public entities in fiscal years beginning after December 15, 2024. Early adoption is permitted. The Company does not expect the adoption of the new guidance will have a material impact on the Company’s consolidated financial statements and related disclosures. Recently Adopted Accounting Pronouncements There are no recently adopted accounting pronouncements.

ACQUISITION

ACQUISITION	12 Months Ended
ACQUISITION	Dec. 31, 2023
Business Combination and Asset Acquisition [Abstract]
ACQUISITION	ACQUISITION On October 3, 2022, the Company completed the acquisition of the assets of Gunner Made LLC (“Gunner”), a wholly owned entity of PNG Holdings LLC, a design and animation studio based in Detroit, Michigan. The acquisition of Gunner added fifteen new designers, illustrators, and animators to Duolingo’s existing design teams. The total consideration was $4.5 million, of which $4 million was purchase price paid in cash upon closing and was allocated to Goodwill within the Consolidated Financial Statements as it was determined that no other separately identifiable assets were acquired. The remaining $450 was paid out in October 2023 after one year of continued service of certain Gunner employees, and was expensed over the period within General and administrative in the Consolidated Statements of Operations and Comprehensive Income (Loss). During 2022, the Company incurred $50 of acquisition costs related to due diligence and valuation, and they are included in General and administrative expense within the Consolidated Statements of Operations and Comprehensive Income (Loss). The Company assumed a new lease for office space as part of the Gunner acquisition in 2022. The term of the newly acquired lease was 68 months beginning on October 3, 2022 and expiring on May 31, 2028. The Company has the option to extend the lease for one additional term of five years and one additional term of four years which the Company has not included in the lease term. The remaining payments related to this lease agreement as of December 31, 2022 were approximately $750. The Company reviewed the lease, and determined that the current terms were relative to current market conditions, and as such, no intangible asset was created. The Company also signed an agreement to sublease a portion of the acquired lease. The term of the sublease was 68 months beginning on October 3, 2022 and expiring on May 31, 2028. The remaining receivable related to this sublease agreement as of December 31, 2022 was approximately $358.

REVENUE

REVENUE	12 Months Ended
REVENUE	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
REVENUE	REVENUE The Company has four predominant sources of revenues; time-based subscriptions, in-app advertising placement by third parties, the Duolingo English Test, and In-App Purchases. Revenue is recognized upon transfer of control of promised products or services to users in an amount that reflects the consideration the Company expects to receive in exchange for those services. The Company does not enter into contracts with a customer that contain multiple promises that result in multiple performance obligations. Revenue is recorded net of taxes assessed by a government authority that are both imposed on and concurrent with specific revenue transactions between us and our users. Revenue from time-based subscriptions includes a stand-ready obligation to provide hosting services that are consumed by the customer over the subscription period. Users can purchase Duolingo monthly or they can purchase a year-long subscription and pay for the subscription at the time of purchase. Under the year-long subscription, users can also purchase a single plan or a family plan. The family plan includes up to six users on one subscription. Such payments are initially recorded to deferred revenue. The user has the ability to download limited content offline. However, as there is a significant level of integration and interdependency with the online functionality, the Company considers the service to be a single performance obligation for the online and offline content. The Company enters into arrangements with advertising networks to monetize the in-app advertising inventory. Revenue from in-app advertising placement is recognized at a point in time when the advertisement is placed and is based upon the amount received. Duolingo English Test revenue is generally recognized once the tests have gone through the proctoring process and a certification decision has been made. This process usually takes less than 48 hours after the test has been completed and uploaded. Customers have 21 days from the date of purchase to take the exam or their purchase will expire and revenue will be recognized. Virtually all customers complete their exams prior to expiration. Sometimes organizations may purchase tests in bulk via coupons with a one year expiration date. The Company will defer revenue from all tests that have neither been proctored nor expired. The Company’s users have the option to purchase consumable in-app virtual goods. The Company recognizes revenue over the period in which the user consumes the virtual good, which is generally within a month. The Company also recognizes revenue from Duo’s Taquería , a restaurant that opened during 2022, in the space adjacent to our headquarters in Pittsburgh. Revenue from Duo’s Taquería is recognized at a point in time when the sales are made. Principal Agent Considerations —The Company makes its application available to be downloaded through third-party digital distribution service providers. Users who purchase subscriptions also pay through the respective app stores. The Company evaluates the purchases via third-party payment processors to determine whether its revenues should be reported gross or net of fees retained by the payment processor. The Company is the principal in the transaction with the end user as a result of controlling, hosting, and integrating the delivery of the virtual items to the end user. The Company records revenue gross as a principal and records fees paid to third-party payment processors as Cost of revenues. Contract Balances —Deferred revenue mostly consists of payments we receive in advance of revenue recognition, and is mostly related to time-based subscriptions, which will be recognized into revenue over the course of the upcoming year (recognized over 12 months or less). Additionally, the Duolingo English Test has deferred revenue related to tests that have been purchased, but will not be recognized until the tests have been proctored. Disaggregation of Revenue In accordance with ASC 606, Revenue from Contracts with Customers , the Company disaggregates revenue from contracts with customers into revenue streams, which most closely depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. Year Ended December 31, (In thousands) 2023 2022 2021 Revenues: Subscription $ 404,684 $ 273,507 $ 180,698 Advertising 49,858 44,731 38,501 Duolingo English Test 41,212 32,718 24,658 In-App Purchases 34,673 17,914 6,836 Other (1) 682 625 79 Total revenues $ 531,109 $ 369,495 $ 250,772 ________________ (1) Other revenue is mainly comprised of revenue from Duo’s Taquería. Information regarding geography of revenues is based upon the location where the users are located or, in the case of the Duolingo English Test, where the tests are taken: Year Ended December 31, 2023 2022 2021 United States $ 238,759 $ 168,320 $ 109,163 United Kingdom 42,118 31,539 25,163 Rest of World 250,232 169,636 116,446 Total $ 531,109 $ 369,495 $ 250,772 Customers located in the United States accounted for 45%, 46% and 44% of total revenues for the year ended December 31, 2023, 2022 and 2021, respectively, and customers located in the United Kingdom accounted for 8%, 9% and 10% for the years ended December 31, 2023, 2022 and 2021, respectively. No other country accounted for more than 10% of revenue in the periods presented. Changes in deferred revenues were as follows: Year Ended December 31, (In thousands) 2023 2022 Beginning balance—January 1 $ 157,550 $ 98,267 Amount from beginning balance recognized into revenue (157,550) (98,267) Recognition of deferred revenue (287,429) (199,130) Deferral of revenue 536,621 356,680 Ending balance—December 31 $ 249,192 $ 157,550

PROPERTY and EQUIPMENT, net

PROPERTY and EQUIPMENT, net	12 Months Ended
PROPERTY and EQUIPMENT, net	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
PROPERTY and EQUIPMENT, net	PROPERTY and EQUIPMENT, net Property and equipment consists of the following as of December 31, 2023 and December 31, 2022: (In thousands) 2023 2022 Leasehold improvements $ 18,191 $ 15,983 Furniture, fixtures and equipment 5,869 5,204 Total property and equipment 24,060 21,187 Less: accumulated depreciation (12,268) (8,218) Total property and equipment, net $ 11,792 $ 12,969 Depreciation expense is included within the following financial statement line items within the Company’s Consolidated Statements of Operations and Comprehensive Income (Loss). Year Ended December 31, (In thousands) 2023 2022 2021 Research and development $ 1,650 $ 1,500 $ 260 Sales and marketing 190 190 32 General and administrative 2,260 1,428 1,741 Total $ 4,100 $ 3,118 $ 2,033

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	12 Months Ended
INTANGIBLE ASSETS AND GOODWILL	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL Intangible assets consist of the following as of December 31, 2023 and December 31, 2022: (In thousands) 2023 2022 Capitalized software $ 26,895 $ 16,809 Other intangible assets 117 18 Total intangible assets 27,012 16,827 Less: accumulated amortization (11,017) (8,330) Intangible assets, net $ 15,995 $ 8,497 The Company capitalized $10,394 and $5,665 of software development costs during the year ended December 31, 2023 and 2022, respectively. Amortization expense is included within the following financial statement line items within the Company’s Consolidated Statements of Operations and Comprehensive Income (Loss). Year Ended December 31, (In thousands) 2023 2022 2021 Cost of revenues $ 2,020 $ 870 $ — Sales and marketing 975 882 693 Total $ 2,995 $ 1,752 $ 693

LEASES

LEASES	12 Months Ended
LEASES	Dec. 31, 2023
Leases [Abstract]
LEASES	LEASES The Company has entered into various operating leases for its office space expiring between fiscal 2024 and 2035. Certain lease agreements contain an option for the Company to renew a lease for a term of up to five years. The Company considers these options, which may be elected at the Company’s sole discretion, in determining the lease term on a lease-by-lease basis. The Company assumed a new lease for office space as part of the Gunner acquisition in 2022. The term of the newly acquired lease was 68 months beginning on October 3, 2022 and expiring on May 31, 2028. The Company has the option to extend the lease for one additional term of five years and one additional term of four years which the Company has not included in the lease term. The Company also signed an agreement to sublease a portion of the acquired lease. The term of the sublease was 68 months beginning on October 3, 2022 and expiring on May 31, 2028. The remaining receivable related to this sublease agreement as of December 31, 2023 was approximately $295. In December 2023, the Company signed an extension for the office space assumed in the prior year as part of the Gunner acquisition. The term of the amended lease is 73 months beginning on December 4, 2023 and expiring on December 31, 2029. The remaining payments related to this lease agreement as of December 31, 2023 are approximately $1,380. The following represents the components of lease cost for the years ended December 31, 2023, 2022 and 2021 along with supplemental disclosures of cash flow information, lease term and discount rate: Year Ended December 31, 2023 2022 2021 Operating lease cost $ 7,459 $ 7,076 $ 1,919 Short term lease cost 48 125 1,266 Variable lease cost 252 63 28 Total lease cost $ 7,759 $ 7,264 $ 3,213 Cash paid for amounts included in the measurement of lease liabilities $ 7,512 $ 5,168 $ 1,819 Right-of-use assets obtained in exchange for new operating lease liabilities $ — $ 909 $ 22,274 Right of use assets disposed or adjusted, modifying operating leases liabilities $ 2,024 $ (1,586) $ (235) Gain from termination of leases $ — $ — $ 31 Weighted-average remaining lease term 9 years 9 years 9 years Weighted-average discount rate 7.38 % 6.92 % 5.77 % Sublease income was immaterial for the years ended December 31, 2023, 2022, and 2021. The following table reconciles future minimum undiscounted rental commitments for operating leases to operating lease liabilities recorded on the Consolidated Balance Sheet as of December 31, 2023: Fiscal year 2024 $ 5,607 2025 3,386 2026 3,399 2027 3,463 2028 3,528 Thereafter 15,735 Total undiscounted lease payments $ 35,118 Present value adjustment (10,080) Operating lease liabilities $ 25,038 Current lease liabilities of $3,944 and $4,903 are presented within Accrued expenses and other liabilities On December 18, 2023, Duolingo, Inc. entered into an Agreement of Sub-Sublease, with Spotify USA Inc., as Sub-Sublandlord for 85,666 square feet of office space in the building located at 4 World Trade Center, 150 Greenwich Street, New York, New York 10007 for use as additional office space. The term of the Sub-Sublease commenced on January 8, 2024 and will expire on April 29, 2034 The initial base rent is $442 per month on a triple net basis, increasing to $478 per month at the beginning of the sixth year In lieu of a security deposit, the Company is obligated to provide an irrevocable stand-by letter of credit to the Sub-Sublandlord. This letter of credit acts as security for the faithful performance by the Company of all terms, covenants and conditions of the lease agreement. The cash collateral and deposits for the letters of credit have been recognized as restricted cash in the consolidated balance sheets and totaled $2,735 and $0 as of December 31, 2023 and December 31, 2022, respectively. As the lease’s commencement date is January 2024, it is not included within the Consolidated Balance Sheet for the year ended December 31, 2023.

INCOME TAXES

INCOME TAXES	12 Months Ended
INCOME TAXES	Dec. 31, 2023
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES For the years ended December 31, 2023, 2022 and 2021 income (loss) before income taxes included the following components: Year Ended December 31, 2023 2022 2021 Domestic $ 16,501 $ (60,099) $ (59,737) Foreign 1,276 1,463 (221) Total $ 17,777 $ (58,636) $ (59,958) For the years ended December 31, 2023, 2022 and 2021 the Company recognized the following provision for income taxes: Year Ended December 31, 2023 2022 2021 Current: Federal $ 895 $ 302 $ — State 607 327 80 Foreign 341 524 97 Total $ 1,843 $ 1,153 $ 177 Deferred: Federal $ — $ — $ — State — — — Foreign (133) (215) — Total $ (133) $ (215) $ — Total provision for income taxes $ 1,710 $ 938 $ 177 The provision for income taxes differs from the amounts computed by applying the federal statutory rate as follows for the years ended December 31, 2023, 2022 and 2021: 2023 2022 2021 Expected income tax expense at federal statutory rate 21.0 % 21.0 % 21.0 % State taxes, net of Federal income tax effect (35.1) 6.7 6.5 Section 162(m) limitation 56.5 (15.2) (13.5) Equity compensation (208.4) 28.4 53.8 Meals and entertainment 5.6 (1.2) (0.5) Foreign-Derived Intangible Income deduction (13.4) — — Other permanent adjustments 2.2 0.3 — Research and development credit (76.4) 11.7 15.9 Valuation allowance 257.6 (53.3) (83.5) Effective income tax rate 9.6 % (1.6) % (0.3) % The 2023 effective tax rate differs from the statutory rate as a result of an increase in tax deductible stock-based compensation and the generation of research and development tax credits offset by an increase in the valuation allowance for the Company’s net deferred tax assets. For 2022 and 2021, the effective tax rate is less than the statutory rate primarily as a result of the valuation allowance for the Company’s net deferred tax assets. The Company has the following deferred tax assets (liabilities) as of December 31, 2023 and 2022: 2023 2022 Net operating loss carryforwards $ 15,533 $ 42,861 Stock-based compensation 5,207 3,605 Research and development credits 38,146 22,386 Lease liability 5,739 6,487 Section 174 research and development capitalization 102,055 42,429 Marketing and advertising 766 633 Sales tax / Value added tax ("VAT") reserve 397 210 Other deferred tax assets 65 140 Valuation allowance (156,870) (108,504) Total deferred tax assets 11,038 10,247 ROU asset (4,354) (5,122) Property and equipment (2,164) (2,569) Capitalized software (3,716) (1,913) Other deferred tax liabilities (38) (10) Total deferred tax liabilities (10,272) (9,614) Net deferred taxes $ 766 $ 633 The Company has provided a full valuation allowance for its U.S. federal and state net deferred tax asset as it is not more likely than not that the asset will be realized. The movement in valuation allowance of $48,366 is primarily related to the: • increase to the deferred tax assets for the capitalization of research and development expenditures under Section 174, which was a change in tax law from the Tax Cuts and Job Acts of 2017, which went into effect in January 2022, • an increase in the generation of research and development tax credits, and • a reduction in the Company’s net operating losses. The Company has a deferred tax asset with respect to its China subsidiary, against which no valuation allowance has been recorded. The following table represents the activity in our valuation allowance for the years ended December 31, 2023 and 2022: Year Ended December 31, 2023 2022 Beginning balance—January 1 $ (108,504) $ (76,293) Valuation allowances established (48,366) (32,211) Release of valuation allowances — — Ending balance—December 31 $ (156,870) $ (108,504) The Company has approximately $48,866 in federal net operating loss carryforwards and approximately $71,422 in state net operating loss carryforwards. Certain of these loss carryforwards have an indefinite life and other amounts are available to offset future taxable income through 2043. The Company has approximately $38,146 in federal and state general business credits that are available to offset future taxable income through 2043. The Company has analyzed the impact of Internal Revenue Code (“IRC”) Sections 382 and 383 on these tax attributes and has determined that no prior ownership changes have occurred which would limit the Company’s ability to utilize the NOLs and research and development tax credits. The Company’s tax years through the 2023 tax year remain subject to examination by federal and state tax authorities. The Company utilizes a more-likely-than-not standard in recognizing a tax benefit in its financial statements. No uncertain tax benefits have been recorded in 2023, 2022, and 2021, respectively.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
STOCK-BASED COMPENSATION	Dec. 31, 2023
Equity [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION Prior to the IPO, the Company granted options to purchase shares of the Company’s common stock and restricted stock units (“RSU”) in respect of shares of the Company’s common stock to employees, directors and consultants under the Company’s 2011 Equity Incentive Plan. In July 2021, Duolingo adopted the 2021 Incentive Award Plan (“2021 Plan”) and the 2021 Employee Stock Purchase Plan (“ESPP”), each of which became effective on July 26, 2021 in connection with the IPO. An aggregate of 7,946 shares and 1,119 shares of Class A common stock were made available for future issuance under the 2021 Plan and ESPP, respectively. On each January 1, the number of shares of the Company’s Class A common stock available for issuance under the 2021 Plan have been, and through January 1, 2031, will be, increased by the lesser of (i) 5% of the shares outstanding on the preceding December 31 (calculated on an as-converted basis) and (ii) such smaller number of shares of common stock as determined by the Board or the Committee (as defined in the 2021 Plan). On January 1, 2024, the 2021 Plan was increased by 2,126 shares of common stock. The Board waived the 2024 automatic annual increase of shares available for future issuance under the ESPP and the Company intends to waive such automatic annual increase for all applicable future periods. The Company’s stock options vest based on terms in the stock option agreements, which generally provide for vesting over four years based on continued service to the Company and its subsidiaries. Each option has a term of ten years. Stock options granted under the 2021 Plan must generally have an exercise price of not less than the estimated fair market value of the underlying Class A common stock at the date of the grant. No options have been granted under the 2021 Plan. A summary of stock option activity under the Plans was as follows: (In thousands, except prices and years) Number of Weighted- Weighted- average remaining contractual life (years) Aggregate intrinsic value Options outstanding at January 1, 2023 4,410 $ 14.04 6.25 $ 251,832 Granted (1) — Exercised (1,396) 9.76 Forfeited and expired (29) 14.09 Options outstanding at December 31, 2023 2,985 $ 16.04 5.60 $ 629,865 Options exercisable at December 31, 2023 2,817 $ 15.54 5.54 $ 594,157 ________________ (1) There were no stock options granted during the years ended December 31, 2023 and 2022. The total intrinsic value of options exercised was approximately $192,456, $140,884 and $194,513 for the periods ended December 31, 2023, 2022 and 2021, respectively. The fair value of each option grant is estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: 2023 2022 2021 Risk-free interest rate n/a n/a 1.04 – 1.14% Expected life n/a n/a 5.90 years Expected volatility n/a n/a 48.90 – 49.12% Dividend yield n/a n/a —% Fair value of common stock n/a n/a $38.08 – $52.80 The risk-free interest rate is based on the U.S. treasury yield curve in effect as of the grant date. When establishing the expected life assumptions, the Company annually reviews historical employee exercise behavior of option grants and other economic data impacting the period the stock options are expected to remain outstanding. Expected volatility is determined using a benchmark index of similar public companies. The Company based the assumed dividend yield on its expectation of not paying dividends in the foreseeable future. Because the Company’s common stock was not yet publicly traded at the time the options were granted, the Company estimated the fair value of common stock. The Board estimated the fair value of the common stock at the time awards were granted based on factors such as valuations of comparable companies, the status of the Company’s development and sales efforts, revenue growth, and additional objective and subjective factors relating to the Company’s business. A summary of RSU activity under the Plans was as follows: (In thousands, except prices) Restricted stock units Weighted- Outstanding at January 1, 2023 2,036 $ 85.74 Granted 873 138.99 Released (673) 89.58 Forfeited (209) 96.23 Outstanding at December 31, 2023 2,027 $ 106.32 Prior to July 30, 2021, no stock-based compensation expense had been recognized for RSUs because the liquidity-based vesting condition had not been probable of being satisfied. Upon the IPO, the liquidity-based vesting condition was met and $2,035 of stock-based compensation expense was recognized related to these awards. As of December 31, 2023, there was approximately $1,393 of unrecognized compensation cost related to stock options granted under the plans with a weighted-average period of approximately seven months. The amount of unrecognized compensation expense for RSUs as of December 31, 2023 was $200,433 with a weighted-average period of approximately three years. Total unrecognized compensation expense as of December 31, 2023 was $201,826. There were 9,404 shares available for grant at December 31, 2023. Performance-based RSUs In June 2021, the Company granted an aggregate of 1,800 performance-based RSUs (the “Founder Awards”) to the Company’s founders. The Founder Awards vest upon the satisfaction of both a service-based condition and a performance-based condition and generally are settled one year after vesting. The service-based condition is satisfied as to 25% of the Founder Awards on each anniversary of the IPO on July 27, 2021, subject to the continuous service of the founders through the applicable date. The performance-based condition will be satisfied with respect to each of 10 equal tranches only if the trailing 60-calendar day volume-weighted-average closing trading price of the Company’s Class A common stock reaches certain stock-price hurdles for each such tranche, as set forth below, over a period of 10 years from the date of grant. Any RSUs associated with stock-prices hurdle not achieved by the tenth anniversary of the date of grant will terminate and be canceled for no additional consideration to the founders. The stock-price hurdles and number of RSUs eligible to vest will be adjusted to reflect any stock splits, stock dividends, combinations, reorganizations, reclassifications, or similar events under the 2021 Plan. The Founder Awards will be settled in shares of the Company’s Class B common stock. Tranche Company Stock Price Hurdle Number of RSUs Eligible to Vest 1 $ 127.50 90 2 $ 153.00 90 3 $ 178.50 90 4 $ 204.00 180 5 $ 255.00 180 6 $ 306.00 180 7 $ 357.00 180 8 $ 408.00 180 9 $ 612.00 270 10 $ 816.00 360 The Company estimated the grant date fair value of the Founder Awards using a model based on multiple stock-price paths developed through the use of a Monte Carlo simulation that incorporates into the valuation the possibility that the stock-price hurdles may not be satisfied. The weighted-average grant date fair value of the Founder Awards was estimated to be $61.56 per share using the below inputs. Input Assumption Valuation Date June 28, 2021 Risk-free interest rate 1.48% Expected life 9.98 Expected volatility 51.67% Dividend yield 0.00% Fair value of common stock $95.00 The Company estimates that it will recognize total stock-based compensation expense of approximately $110,817 over the derived service period of each of the ten separate tranches which is between 3.58 – 5.92 years. If the stock-price hurdles are met sooner than the requisite service period, the stock-based compensation expense will be adjusted to prospectively recognize the remaining expense over the remaining derived service period. Provided that the founders continue to provide services to the Company, stock-based compensation expense is recognized over the derived service period, regardless of whether the stock-price hurdles are achieved. The stock-price hurdles for the first two tranches were met during 2021. With respect to these two tranches in combination, the service-based condition was satisfied during the three months ended September 30, 2023. Of the 180 shares underlying RSUs released, an aggregate of 96 shares were disbursed to the founders in a net-share settlement, and 84 shares were withheld by the Company to cover the founders’ tax withholding obligations. The shares withheld by the Company were added to the shares of Class A common stock available for issuance under the 2021 Plan. The stock-price hurdles for the third and fourth tranches were met during the three months ended December 31, 2023. As of the date of this Annual Report on Form 10-K, no additional stock-price hurdles have been met. The Company recognized $26,622, $30,997 and $16,463 for the years ended December 31, 2023, 2022 and 2021 respectively, which is included within General and administrative in the Consolidated Statements of Operations and Comprehensive Income (Loss). As of December 31, 2023, there is $36,735 of unrecognized compensation expense related to these awards. In February 2021, the Company initiated a tender offer which allowed employees to sell up to 10% of their vested options or shares back to the Company at a selling price of $59.77, which was above fair market value of $38.08. The Company paid $13,479 and incurred $5,275 of additional compensation expense related to this tender representing the difference between the aggregate selling price and fair market value of the options and shares sold, and a $7,335 decrease to Additional paid-in capital. As a result of this tender, 220 options were put back into the option pool and 23 shares were retired with an $868 decrease to Additional paid-in capital. Upon the IPO, vesting of stock option grants to certain executive officers were accelerated, which resulted in an additional $5,574 of compensation expense during the year ended December 31, 2021. This is included within General and administrative in the Consolidated Statements of Operations and Comprehensive Income (Loss). Total stock-based compensation expense was $95,221, $73,820 and $40,804 for the years ended December 31, 2023, 2022 and 2021, respectively. Stock based compensation expense is included in the Consolidated Statements of Operations and Comprehensive Income (Loss) as shown in the following table: Year Ended December 31, (In thousands) 2023 2022 2021 Cost of revenues $ 55 $ 38 $ 8 Research and development 45,119 26,373 9,298 Sales and marketing 3,908 2,540 881 General and administrative 46,139 44,869 30,617 Total $ 95,221 $ 73,820 $ 40,804 Nominal amounts of stock based compensation expense is capitalized into intangible assets for the years ended December 31, 2023, 2022 and 2021.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Legal Proceedings — From time to time, the Company may become involved in various legal proceedings in the ordinary course of its business and may be subject to third-party infringement claims. The outcome of any such claims or proceedings, regardless of the merits, is inherently uncertain. The Company is not currently party to any material legal proceedings. Related Parties — The Company has determined that there were no transactions with related parties as of or during the years ended December 31, 2023, 2022 and 2021. Letters of Credit

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	12 Months Ended
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	Dec. 31, 2023
Other Liabilities Disclosure [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following: (In thousands) December 31, December 31, 2022 Marketing-related accruals $ 4,732 $ 3,464 Employee-related costs 4,494 4,233 Sales and VAT tax accrual 4,365 2,396 Obligations under current leases 3,944 4,903 Hosting costs 3,079 2,102 Other 4,317 4,872 Total $ 24,931 $ 21,970

EMPLOYEE BENEFIT PLAN

EMPLOYEE BENEFIT PLAN	12 Months Ended
EMPLOYEE BENEFIT PLAN	Dec. 31, 2023
Postemployment Benefits [Abstract]
EMPLOYEE BENEFIT PLAN	EMPLOYEE BENEFIT PLAN The Company sponsors a profit sharing plan with a 401(k) feature, the Duolingo Retirement Plan (the “Plan”), for eligible employees. The current Plan, effective January 1, 2021, provides for Company safe harbor matching contributions of 100% of the first 4% of the employees’ elective deferrals and 50% of the next 2%, with vesting starting upon the first day of employment. The Company also has the option to make discretionary matching or profit sharing contributions. The Company made safe harbor matching contributions of approximately $5,908, $4,624 and $3,438 during the years ended December 31, 2023, 2022 and 2021, respectively. The Company did not make any discretionary matching or profit sharing contributions during the years ended December 31, 2023, 2022 and 2021.

EARNINGS (LOSS) PER SHARE

EARNINGS (LOSS) PER SHARE	12 Months Ended
EARNINGS (LOSS) PER SHARE	Dec. 31, 2023
Earnings Per Share [Abstract]
EARNINGS (LOSS) PER SHARE	EARNINGS (LOSS) PER SHARE Basic and diluted net income (loss) per share attributable to common stockholders is presented in conformity with the two-class method required for participating securities. Basic net income (loss) per share attributable to common stockholders is calculated by dividing the net income (loss) by the weighted-average number of shares of common stock outstanding during the period, less shares subject to repurchase. The diluted net income per share attributable to common stockholders is calculated by giving effect to all potential dilutive common stock equivalents outstanding for the period. The rights, including the liquidation and dividend rights, of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to 20 votes per share. Each share of Class B common stock is convertible into a share of Class A common stock voluntarily at any time by the holder, and automatically upon certain events. The Class A common stock has no conversion rights. As the liquidation and dividend rights are identical for Class A and Class B common stock, the undistributed earnings are allocated on a proportional basis and the resulting net income (loss) per share attributable to common stockholders will, therefore, be the same for both Class A and Class B common stock on an individual or combined basis. Year Ended December 31, (In thousands, except per share data) 2023 2022 2021 Numerator: Net income (loss) attributable to Class A and Class B common stockholders $ 16,067 $ (59,574) (60,135) Denominator: Weighted-average shares in computing net income (loss) per share attributable to Class A and Class B common stockholders, basic and diluted 41,451 39,470 23,433 Effect of dilutive securities Founder awards where performance has been met 270 — Dilutive effect of stock options outstanding (1) 2,774 — — RSUs outstanding 2,027 — — Denominator for dilutive net income per common share - weighted-average shares 46,522 39,470 23,433 Basic income (loss) per common share $ 0.39 $ (1.51) $ (2.57) Diluted income (loss) per common share $ 0.35 $ (1.51) $ (2.57) ________________ (1) The Company had 3.0 million options outstanding as of December 31, 2023. The estimated dilutive effect is calculated as the number of shares expected to be issued upon vesting or exercise, adjusted for the strike price proceeds that are received by the Company and assumed to be used to repurchase shares of Duolingo common stock. Since the Company was in a net loss position for the years ended December 31, 2022 and 2021 there is no difference between the number of shares used to calculate basic and diluted loss per share. The potential shares of common stock that were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive are as follows: Year Ended December 31, (In thousands) 2022 2021 Founder awards where performance has been met 180 180 Stock options outstanding 4,410 6,255 RSUs outstanding 2,036 730 Total 6,626 7,165 Founder awards of 1,620, where the performance criteria has not been satisfied, are excluded from the above tables because the stock-price hurdles for those awards had not been met as of December 31, 2022 and 2021.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Dec. 31, 2023
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS In February 2024, the Company signed a lease for office space in Seattle, Washington. The term of the lease is sixty-three months beginning on March 1, 2024 and expiring on May 31, 2029. The expected payments related to this lease are approximately $1,728.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net income (loss) attributable to Class A and Class B common stockholders	$ 16,067	$ (59,574)	$ (60,135)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended	12 Months Ended
Insider Trading Arrangements	Dec. 31, 2023 shares	Dec. 31, 2023 shares
Trading Arrangements, by Individual
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Dr. Luis von Ahn [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On November 30, 2023, Dr. Luis von Ahn, Chief Executive Officer, and the Luis von Ahn Foundation, of which Dr. von Ahn is the Director and President, entered into a 10b5-1 sales plan (the “von Ahn 10b5-1 Sales Plan”) intended to satisfy the affirmative defense of Rule 10b5-1(c) under the Exchange Act, pursuant to which a maximum aggregate of 103,000 shares of the Company’s Class A common stock may be sold (up to 80,000 shares by Dr. von Ahn and up to 23,000 by the Luis von Ahn Foundation). The von Ahn 10b5-1 Sales Plan will remain in effect until the earlier of (1) December 15, 2024, (2) the date on which an aggregate of 103,000 shares of the Company’s common stock have been sold under the von Ahn 10b5-1 Sales Plan, or (3) such time as the von Ahn 10b5-1 Sales Plan is otherwise terminated or expires according to its terms.
Name	Dr. Luis von Ahn,
Title	Chief Executive Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	November 30, 2023
Arrangement Duration	397 days
Aggregate Available	80,000	80,000
Amy Bohutinsky [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On December 4, 2023, Amy Bohutinsky, member of our Board of Directors, entered into a 10b5-1 sales plan (the “Bohutinsky 10b5-1 Sales Plan”) intended to satisfy the affirmative defense of Rule 10b5-1(c) under the Exchange Act which provides for the potential exercise of vested stock options and the associated sale of up to 15,000 shares of the Company’s Class A common stock. The Bohutinsky 10b5-1 Sales Plan will remain in effect until the earlier of (1) December 31, 2024, (2) the date on which an aggregate of 15,000 shares of the Company’s Class A common stock have been sold under the Bohutinsky 10b5-1 Sales Plan, or (3) such time as the Bohutinsky 10b5-1 Sales Plan is otherwise terminated or expires according to its terms.
Name	Amy Bohutinsky
Title	member of our Board of Directors
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	December 4, 2023
Arrangement Duration	393 days
Aggregate Available	15,000	15,000

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation
Basis of Presentation and Accounting Principles	Basis of Presentation Accounting Principles —The Consolidated Financial Statements and accompanying notes are prepared in accordance with GAAP.
Use of Estimates	Use of Estimates— The preparation of Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying notes. Significant estimates and assumptions reflected in the Consolidated Financial Statements include, but are not limited to, useful lives of property and equipment, valuation of deferred tax assets and liabilities, stock-based compensation, common stock valuation, operating lease right-of-use assets and liabilities, capitalization of internally developed software and associated useful lives and contingent liabilities. Actual results may differ materially from such estimates. Management believes that the estimates, and judgments upon which they rely, are reasonable based upon information available to them at the time that these estimates and judgments are made. To the extent that there are material differences between these estimates and actual results, the Company’s Consolidated Financial Statements will be affected.
Revenue Recognition	Revenue Recognition— The Company has four predominant sources of revenue; time-based subscriptions, in-app advertising placement by third parties, the Duolingo English Test, and In-App Purchases. See Footnote 4 for further discussion. Deferred Revenues— Revenue is recognized over the life of the subscription, or in the case of Duolingo English Test, revenue is recognized when the test is proctored. The Company classifies deferred revenue as a short-term liability on the consolidated balance sheets as the longest subscription plan is for twelve months, and Duolingo English Test purchases must be taken within 21 days. Cost of Revenues— Cost of revenue predominantly consists of third-party payment processing fees charged by various distribution channel and hosting fees. To a much lesser extent, includes wages and stock-based compensation for certain employees in the capacity of customer support, amortization of revenue generating capitalized software, and depreciation of certain property and equipment. Deferred Cost of Revenues— Deferred cost of revenue includes third-party payment processing fees amortized over the subscription terms in proportion to the revenue recognized. In situations where fees are charged for subscriptions that exceed one month, costs are deferred and recognized over the life of the subscription and are classified as a current asset. The Company classifies deferred cost of revenue as a short-term asset on the Company’s consolidated balance sheets as the longest subscription plan is for twelve months. The Company has four predominant sources of revenues; time-based subscriptions, in-app advertising placement by third parties, the Duolingo English Test, and In-App Purchases. Revenue is recognized upon transfer of control of promised products or services to users in an amount that reflects the consideration the Company expects to receive in exchange for those services. The Company does not enter into contracts with a customer that contain multiple promises that result in multiple performance obligations. Revenue is recorded net of taxes assessed by a government authority that are both imposed on and concurrent with specific revenue transactions between us and our users. Revenue from time-based subscriptions includes a stand-ready obligation to provide hosting services that are consumed by the customer over the subscription period. Users can purchase Duolingo monthly or they can purchase a year-long subscription and pay for the subscription at the time of purchase. Under the year-long subscription, users can also purchase a single plan or a family plan. The family plan includes up to six users on one subscription. Such payments are initially recorded to deferred revenue. The user has the ability to download limited content offline. However, as there is a significant level of integration and interdependency with the online functionality, the Company considers the service to be a single performance obligation for the online and offline content. The Company enters into arrangements with advertising networks to monetize the in-app advertising inventory. Revenue from in-app advertising placement is recognized at a point in time when the advertisement is placed and is based upon the amount received. Duolingo English Test revenue is generally recognized once the tests have gone through the proctoring process and a certification decision has been made. This process usually takes less than 48 hours after the test has been completed and uploaded. Customers have 21 days from the date of purchase to take the exam or their purchase will expire and revenue will be recognized. Virtually all customers complete their exams prior to expiration. Sometimes organizations may purchase tests in bulk via coupons with a one year expiration date. The Company will defer revenue from all tests that have neither been proctored nor expired. The Company’s users have the option to purchase consumable in-app virtual goods. The Company recognizes revenue over the period in which the user consumes the virtual good, which is generally within a month. The Company also recognizes revenue from Duo’s Taquería , a restaurant that opened during 2022, in the space adjacent to our headquarters in Pittsburgh. Revenue from Duo’s Taquería is recognized at a point in time when the sales are made. Principal Agent Considerations —The Company makes its application available to be downloaded through third-party digital distribution service providers. Users who purchase subscriptions also pay through the respective app stores. The Company evaluates the purchases via third-party payment processors to determine whether its revenues should be reported gross or net of fees retained by the payment processor. The Company is the principal in the transaction with the end user as a result of controlling, hosting, and integrating the delivery of the virtual items to the end user. The Company records revenue gross as a principal and records fees paid to third-party payment processors as Cost of revenues. Contract Balances —Deferred revenue mostly consists of payments we receive in advance of revenue recognition, and is mostly related to time-based subscriptions, which will be recognized into revenue over the course of the upcoming year (recognized over 12 months or less). Additionally, the Duolingo English Test has deferred revenue related to tests that have been purchased, but will not be recognized until the tests have been proctored. Disaggregation of Revenue In accordance with ASC 606, Revenue from Contracts with Customers , the Company disaggregates revenue from contracts with customers into revenue streams, which most closely depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors.
Cash and Cash Equivalents	Cash and Cash Equivalents—
Restricted Cash	Restricted Cash— Restricted cash consists of a collateralized letter of credit established in connection with a lease agreement for the Company’s Sub-Sublease in New York, which was signed in December 2023. Restricted cash is included in non-current assets for leases that expire in more than one year from the balance sheet date.
Accounts Receivable	Accounts Receivable —Accounts receivables are reported on the consolidated balance sheets at the outstanding principal amount adjusted for any allowance for credit losses and any charge offs. The Company provides an allowance for credit losses to reduce trade receivables to their estimated net
Property and Equipment	Property and Equipment —Property and equipment is stated at cost, less accumulated depreciation. Depreciation is computed on the straight-line method. Asset Class Estimated Useful Life Furniture, fixtures and equipment 4 to 6 years Leasehold improvements 5 to 7 years
Goodwill	Goodwill —The Company recognizes the excess of the purchase price over the fair value of identifiable net assets acquired at the acquisition date as goodwill. Goodwill is not amortized but is reviewed for impairment annually and more frequently if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying value. The Company will review goodwill for impairment annually on October 1st of each fiscal year or whenever events or changes in circumstances indicate that an impairment may exist. The Company will first perform a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying value. If the reporting unit does not pass the qualitative assessment, then the reporting unit’s carrying value is compared to its fair value. If the fair value of the reporting unit is greater than the reporting unit’s carrying value, then the carrying value of the reporting unit is deemed to be recoverable. If the carrying value of the reporting unit is greater than the reporting unit’s fair value, goodwill is impaired and written down to the reporting unit’s fair value.
Acquisition	Acquisition —The Company uses the acquisition method of accounting for business combination transactions, and, accordingly, recognizes the fair values of assets acquired and liabilities assumed in our Consolidated Financial Statements. Transaction costs related to the acquisition of the acquired company are expensed as incurred. The allocation of fair values may be subject to adjustment after the initial allocation for up to a one-year period as more information becomes available relative to the fair values as of the acquisition date. The Consolidated Financial Statements include the results of operations of any acquired company since the acquisition date.
Intangible Assets	Intangible Assets —The majority of the Company’s intangible assets is capitalized software, with minimal other intangible assets during the years ended December 31, 2023 and 2022. The Company develops software for internal use and capitalizes the software development costs incurred during the application development stage. Costs incurred prior to and after the application development stage are charged to expense. When the software is ready for its intended use, capitalization ceases and such costs are amortized on a straight-line basis over the estimated life, which is generally three years. Relatively minor upgrades, enhancements and maintenance to the platform are expensed as incurred.
Income Taxes	Income Taxes— The Company provides for income taxes in accordance with the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the carrying amounts of existing assets and liabilities for financial reporting and for income tax reporting. The deferred tax asset or liability represents the future tax return consequences of those difference, which will either be taxable or deductible when the assets and liabilities are recovered or settled. A valuation allowance is established for any deferred tax asset for which it is determined that it is more likely than not that some or all of the deferred tax assets will not be realized. The Company limits the deferred tax assets recognized related to certain officers’ compensation to amounts that it estimates will be deductible in future periods based upon Internal Revenue Code Section 162(m). The Company utilizes a two-step approach to recognizing and measuring uncertain tax positions accounted for in accordance with the asset and liability method. The first step is to evaluate the tax position for recognition by determining whether evidence indicates that it is more likely than not that a position will be sustained if examined by a taxing authority.
Foreign Currency	Foreign Currency —The functional currency of the Company and its subsidiaries is the U.S. dollar. Transactions denominated in currencies other than the functional currency are translated into the functional currency at the exchange rates prevailing at the dates of the transaction. Monetary assets and liabilities denominated in foreign currencies are translated using the exchange rate prevailing at the balance sheet date. Non-monetary assets and liabilities are translated using the historical rate on the date of the transaction. All exchange gains or losses arising from translation of these foreign currency transactions are included in net loss for the year. The Company has not, to the date of these Consolidated Financial Statements, entered into derivative instruments to offset the impact of foreign currency fluctuations.
Fair Value of Financial Instruments	Fair Value of Financial Instruments —The Company accounts for certain assets and liabilities at fair value in accordance with the accounting guidance applicable to fair value measurements and disclosures. The carrying values of cash, cash equivalents, accounts receivable, accounts payable, and accrued expenses are deemed to be reasonable estimates of their fair values because of their short-term nature.
Research and Development Costs	Research and Development Costs
Sales and Marketing	Sales and Marketing
General and Administrative	General and Administrative —General and administrative expense primarily consists of employee-related compensation (including stock-based compensation) for management and administrative functions, including our finance and accounting, legal, and people teams. General and administrative expense also includes certain professional services fees, general corporate and director and officer
Contributors	Contributors— On March 10, 2021, the Company announced that it was ending its non-employee volunteer program, which began in 2013 to build and improve language courses. As part of this change, those contributors who participated in the program became eligible to receive a one-time award, up to an aggregate amount of approximately $4,220, including fees paid to process payments of approximately $526. The Company accounted for this under Financial Accounting Standards Board (“FASB”) Accounting Standards Codifications (“ASC”) 958-720, Not-For-Profit Entities - Other Expenses and ASC 720-25, Contributions Made
Concentration of Credit Risk	Concentration of Credit Risk —The Company’s concentration of credit risk relates to financial institutions holding the Company’s cash and cash equivalents and platforms with significant accounts receivable balances and revenue transactions. The Company maintains cash deposits with financial institutions that may exceed federally insured limits at times. Management believes that the financial institutions that hold the Company’s deposits are financially credit worthy and, accordingly, minimal credit risk exists with respect to those balances.
Stock-Based Compensation	Stock-Based Compensation —The Company accounts for equity-based compensation using the fair value method as set forth in the ASC 718, Compensation—Stock Compensation , which requires the measurement and recognition of compensation expense for all stock-based payment awards based on estimated fair values. This method requires companies to estimate the fair value of stock-based compensation on the date of grant using an option pricing model. The Company estimates the fair value of each equity-based payment award on the date of grant using the Black-Scholes pricing model. The Black-Scholes model determines the fair value of equity-based payment awards based on the fair value of the underlying common stock on the date of grant and requires the use of estimates and assumptions, including the fair value of the Company’s common stock, exercise price of the stock option, expected volatility, expected life, risk-free interest rate and dividend rate. The Company estimates the expected volatility of its stock options by taking the average historical volatility of a group of comparable publicly traded companies over a period equal to the expected life of the options; it is not practical for the Company to estimate its own volatility due to the lack of historical prices. The expected term of the options is determined in accordance with existing equity agreements as the underlying options are assumed to be exercised upon the passage of time. The risk-free interest rate is the estimated average interest rate based on U.S. Treasury zero-coupon notes with terms consistent with the expected life of the awards. The expected dividend yield is zero as the Company does not anticipate paying any recurring cash dividends in the foreseeable future. The Company accounts for forfeitures as they occur. Restricted Stock Units (RSUs) The Company began to grant RSUs in November 2020. The fair value of RSUs is estimated based on the fair value of the Company’s common stock on the date of grant. Each RSU award granted prior to the IPO vests based upon the satisfaction, during the term of the RSUs, of two requirements: length of service and a liquidity event defined as a change in control or a qualified IPO. The service-based vesting condition for the majority of these awards is satisfied over four years. The liquidity-based vesting condition is satisfied upon the occurrence of a qualifying liquidity event. The Company measures and recognizes compensation expense for all stock-based awards based on the estimated fair value of the award. Prior to July 30, 2021, no stock-based compensation expense had been recognized for RSUs because the liquidity-based vesting condition had not been probable of being satisfied. Upon the IPO, the liquidity-based vesting condition was satisfied and $2,035 of stock-based compensation expense was recognized related to these awards during the year ended December 31, 2021. Of that amount, $1,332, $210 and $493 was included within Research and development, Sales and marketing and General and administrative, respectively, in the Consolidated Statements of Operations and Comprehensive Income (Loss). Performance-based RSUs
Contingencies	Contingencies —The Company records accruals for contingencies and legal proceedings expected to be incurred in connection with a loss contingency when it is probable that a liability has been incurred and the amount can be reasonably estimated. If a loss contingency is not probable, but is reasonably possible, or is probable but cannot be estimated, the nature of the contingent liability, together with an estimate of the range of possible loss, would be disclosed.
Segment	Segment —The Company operates as a single operating segment. The chief operating decision maker of the Company is its Chief Executive Officer, who makes resource allocation decisions and assesses performance based on financial information presented on a consolidated basis, accompanied by disaggregated information of our revenue. Accordingly, the Company has determined that it has a single reportable segment and operating segment structure, and operates as one reporting unit.
Leases	Leases —The Company accounts for leases in accordance with ASC 842, Leases , which requires virtually all leases, other than leases that meet the definition of a short-term lease, to be recorded on the balance sheet with a right-of-use (“ROU”) asset and corresponding lease liability. ROU assets are periodically reviewed for impairment whenever events or changes in circumstances arise. During the years ended December 31, 2023, 2022 and 2021, the Company incurred no impairment charges on ROU assets.
Impairment of long-lived assets	Impairment of long-lived assets—
Recently Issued Pronouncements Not Yet Adopted and Recently Adopted Accounting Pronouncements	Recently Issued Pronouncements Not Yet Adopted There are no recently issued accounting pronouncements that the Company has not yet adopted that they believe are applicable or would have a material impact on the financial statements of the Company. In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-07, Segment Reporting (Topic 280), which improves reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. The standard is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The Company does not expect the adoption of the new guidance will have a material impact on the Company’s consolidated financial statements and related disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740), which includes improvements to income tax disclosures. The standard is effective for public entities in fiscal years beginning after December 15, 2024. Early adoption is permitted. The Company does not expect the adoption of the new guidance will have a material impact on the Company’s consolidated financial statements and related disclosures. Recently Adopted Accounting Pronouncements There are no recently adopted accounting pronouncements.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	Dec. 31, 2023
Accounting Policies [Abstract]
Schedule of Cash and Cash Equivalents	The following table shows the breakout between cash and money market funds. December 31, December 31, Cash $ 50,373 $ 91,189 Money market funds 697,237 516,991 Total $ 747,610 $ 608,180
Property, Plant and Equipment	Asset Class Estimated Useful Life Furniture, fixtures and equipment 4 to 6 years Leasehold improvements 5 to 7 years Property and equipment consists of the following as of December 31, 2023 and December 31, 2022: (In thousands) 2023 2022 Leasehold improvements $ 18,191 $ 15,983 Furniture, fixtures and equipment 5,869 5,204 Total property and equipment 24,060 21,187 Less: accumulated depreciation (12,268) (8,218) Total property and equipment, net $ 11,792 $ 12,969 Depreciation expense is included within the following financial statement line items within the Company’s Consolidated Statements of Operations and Comprehensive Income (Loss). Year Ended December 31, (In thousands) 2023 2022 2021 Research and development $ 1,650 $ 1,500 $ 260 Sales and marketing 190 190 32 General and administrative 2,260 1,428 1,741 Total $ 4,100 $ 3,118 $ 2,033

REVENUE (Tables)

REVENUE (Tables)	12 Months Ended
REVENUE (Tables)	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Schedule of Revenue Sources and Streams	Year Ended December 31, (In thousands) 2023 2022 2021 Revenues: Subscription $ 404,684 $ 273,507 $ 180,698 Advertising 49,858 44,731 38,501 Duolingo English Test 41,212 32,718 24,658 In-App Purchases 34,673 17,914 6,836 Other (1) 682 625 79 Total revenues $ 531,109 $ 369,495 $ 250,772 ________________ (1) Other revenue is mainly comprised of revenue from Duo’s Taquería.
Schedule of Revenue by Geographic Areas	Information regarding geography of revenues is based upon the location where the users are located or, in the case of the Duolingo English Test, where the tests are taken: Year Ended December 31, 2023 2022 2021 United States $ 238,759 $ 168,320 $ 109,163 United Kingdom 42,118 31,539 25,163 Rest of World 250,232 169,636 116,446 Total $ 531,109 $ 369,495 $ 250,772
Schedule of Deferred Revenues	Changes in deferred revenues were as follows: Year Ended December 31, (In thousands) 2023 2022 Beginning balance—January 1 $ 157,550 $ 98,267 Amount from beginning balance recognized into revenue (157,550) (98,267) Recognition of deferred revenue (287,429) (199,130) Deferral of revenue 536,621 356,680 Ending balance—December 31 $ 249,192 $ 157,550

PROPERTY and EQUIPMENT, net (Ta

PROPERTY and EQUIPMENT, net (Tables)	12 Months Ended
PROPERTY and EQUIPMENT, net (Tables)	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Asset Class Estimated Useful Life Furniture, fixtures and equipment 4 to 6 years Leasehold improvements 5 to 7 years Property and equipment consists of the following as of December 31, 2023 and December 31, 2022: (In thousands) 2023 2022 Leasehold improvements $ 18,191 $ 15,983 Furniture, fixtures and equipment 5,869 5,204 Total property and equipment 24,060 21,187 Less: accumulated depreciation (12,268) (8,218) Total property and equipment, net $ 11,792 $ 12,969 Depreciation expense is included within the following financial statement line items within the Company’s Consolidated Statements of Operations and Comprehensive Income (Loss). Year Ended December 31, (In thousands) 2023 2022 2021 Research and development $ 1,650 $ 1,500 $ 260 Sales and marketing 190 190 32 General and administrative 2,260 1,428 1,741 Total $ 4,100 $ 3,118 $ 2,033

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	12 Months Ended
INTANGIBLE ASSETS AND GOODWILL (Tables)	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	Intangible assets consist of the following as of December 31, 2023 and December 31, 2022: (In thousands) 2023 2022 Capitalized software $ 26,895 $ 16,809 Other intangible assets 117 18 Total intangible assets 27,012 16,827 Less: accumulated amortization (11,017) (8,330) Intangible assets, net $ 15,995 $ 8,497
Finite-lived Intangible Assets Amortization Expense	Amortization expense is included within the following financial statement line items within the Company’s Consolidated Statements of Operations and Comprehensive Income (Loss). Year Ended December 31, (In thousands) 2023 2022 2021 Cost of revenues $ 2,020 $ 870 $ — Sales and marketing 975 882 693 Total $ 2,995 $ 1,752 $ 693

LEASES (Tables)

LEASES (Tables)	12 Months Ended
LEASES (Tables)	Dec. 31, 2023
Leases [Abstract]
Summary of Components of Lease Cost	The following represents the components of lease cost for the years ended December 31, 2023, 2022 and 2021 along with supplemental disclosures of cash flow information, lease term and discount rate: Year Ended December 31, 2023 2022 2021 Operating lease cost $ 7,459 $ 7,076 $ 1,919 Short term lease cost 48 125 1,266 Variable lease cost 252 63 28 Total lease cost $ 7,759 $ 7,264 $ 3,213 Cash paid for amounts included in the measurement of lease liabilities $ 7,512 $ 5,168 $ 1,819 Right-of-use assets obtained in exchange for new operating lease liabilities $ — $ 909 $ 22,274 Right of use assets disposed or adjusted, modifying operating leases liabilities $ 2,024 $ (1,586) $ (235) Gain from termination of leases $ — $ — $ 31 Weighted-average remaining lease term 9 years 9 years 9 years Weighted-average discount rate 7.38 % 6.92 % 5.77 %
Schedule of Future Minimum Rental Payments for Operating Leases	The following table reconciles future minimum undiscounted rental commitments for operating leases to operating lease liabilities recorded on the Consolidated Balance Sheet as of December 31, 2023: Fiscal year 2024 $ 5,607 2025 3,386 2026 3,399 2027 3,463 2028 3,528 Thereafter 15,735 Total undiscounted lease payments $ 35,118 Present value adjustment (10,080) Operating lease liabilities $ 25,038

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
INCOME TAXES (Tables)	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of Income (Loss) Before Income Tax, Domestic and Foreign	For the years ended December 31, 2023, 2022 and 2021 income (loss) before income taxes included the following components: Year Ended December 31, 2023 2022 2021 Domestic $ 16,501 $ (60,099) $ (59,737) Foreign 1,276 1,463 (221) Total $ 17,777 $ (58,636) $ (59,958)
Schedule of Effective Income Tax Rate Reconciliation	For the years ended December 31, 2023, 2022 and 2021 the Company recognized the following provision for income taxes: Year Ended December 31, 2023 2022 2021 Current: Federal $ 895 $ 302 $ — State 607 327 80 Foreign 341 524 97 Total $ 1,843 $ 1,153 $ 177 Deferred: Federal $ — $ — $ — State — — — Foreign (133) (215) — Total $ (133) $ (215) $ — Total provision for income taxes $ 1,710 $ 938 $ 177 The provision for income taxes differs from the amounts computed by applying the federal statutory rate as follows for the years ended December 31, 2023, 2022 and 2021: 2023 2022 2021 Expected income tax expense at federal statutory rate 21.0 % 21.0 % 21.0 % State taxes, net of Federal income tax effect (35.1) 6.7 6.5 Section 162(m) limitation 56.5 (15.2) (13.5) Equity compensation (208.4) 28.4 53.8 Meals and entertainment 5.6 (1.2) (0.5) Foreign-Derived Intangible Income deduction (13.4) — — Other permanent adjustments 2.2 0.3 — Research and development credit (76.4) 11.7 15.9 Valuation allowance 257.6 (53.3) (83.5) Effective income tax rate 9.6 % (1.6) % (0.3) %
Schedule of Deferred Tax Assets and Liabilities	The Company has the following deferred tax assets (liabilities) as of December 31, 2023 and 2022: 2023 2022 Net operating loss carryforwards $ 15,533 $ 42,861 Stock-based compensation 5,207 3,605 Research and development credits 38,146 22,386 Lease liability 5,739 6,487 Section 174 research and development capitalization 102,055 42,429 Marketing and advertising 766 633 Sales tax / Value added tax ("VAT") reserve 397 210 Other deferred tax assets 65 140 Valuation allowance (156,870) (108,504) Total deferred tax assets 11,038 10,247 ROU asset (4,354) (5,122) Property and equipment (2,164) (2,569) Capitalized software (3,716) (1,913) Other deferred tax liabilities (38) (10) Total deferred tax liabilities (10,272) (9,614) Net deferred taxes $ 766 $ 633
Summary of Valuation Allowance	The following table represents the activity in our valuation allowance for the years ended December 31, 2023 and 2022: Year Ended December 31, 2023 2022 Beginning balance—January 1 $ (108,504) $ (76,293) Valuation allowances established (48,366) (32,211) Release of valuation allowances — — Ending balance—December 31 $ (156,870) $ (108,504)

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
STOCK-BASED COMPENSATION (Tables)	Dec. 31, 2023
Equity [Abstract]
Share-based Payment Arrangement, Option, Activity	A summary of stock option activity under the Plans was as follows: (In thousands, except prices and years) Number of Weighted- Weighted- average remaining contractual life (years) Aggregate intrinsic value Options outstanding at January 1, 2023 4,410 $ 14.04 6.25 $ 251,832 Granted (1) — Exercised (1,396) 9.76 Forfeited and expired (29) 14.09 Options outstanding at December 31, 2023 2,985 $ 16.04 5.60 $ 629,865 Options exercisable at December 31, 2023 2,817 $ 15.54 5.54 $ 594,157 ________________ (1) There were no stock options granted during the years ended December 31, 2023 and 2022.
Share-based Payment Arrangement, Option, Valuation Assumptions	The fair value of each option grant is estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: 2023 2022 2021 Risk-free interest rate n/a n/a 1.04 – 1.14% Expected life n/a n/a 5.90 years Expected volatility n/a n/a 48.90 – 49.12% Dividend yield n/a n/a —% Fair value of common stock n/a n/a $38.08 – $52.80
Share-based Payment Arrangement, RSU, Activity	A summary of RSU activity under the Plans was as follows: (In thousands, except prices) Restricted stock units Weighted- Outstanding at January 1, 2023 2,036 $ 85.74 Granted 873 138.99 Released (673) 89.58 Forfeited (209) 96.23 Outstanding at December 31, 2023 2,027 $ 106.32
Share-based Payment Arrangement, Payment Award	Tranche Company Stock Price Hurdle Number of RSUs Eligible to Vest 1 $ 127.50 90 2 $ 153.00 90 3 $ 178.50 90 4 $ 204.00 180 5 $ 255.00 180 6 $ 306.00 180 7 $ 357.00 180 8 $ 408.00 180 9 $ 612.00 270 10 $ 816.00 360 Input Assumption Valuation Date June 28, 2021 Risk-free interest rate 1.48% Expected life 9.98 Expected volatility 51.67% Dividend yield 0.00% Fair value of common stock $95.00
Share-based Payment Arrangement, Expensed, Amount	Stock based compensation expense is included in the Consolidated Statements of Operations and Comprehensive Income (Loss) as shown in the following table: Year Ended December 31, (In thousands) 2023 2022 2021 Cost of revenues $ 55 $ 38 $ 8 Research and development 45,119 26,373 9,298 Sales and marketing 3,908 2,540 881 General and administrative 46,139 44,869 30,617 Total $ 95,221 $ 73,820 $ 40,804

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	Dec. 31, 2023
Other Liabilities Disclosure [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: (In thousands) December 31, December 31, 2022 Marketing-related accruals $ 4,732 $ 3,464 Employee-related costs 4,494 4,233 Sales and VAT tax accrual 4,365 2,396 Obligations under current leases 3,944 4,903 Hosting costs 3,079 2,102 Other 4,317 4,872 Total $ 24,931 $ 21,970

EARNINGS (LOSS) PER SHARE (Tabl

EARNINGS (LOSS) PER SHARE (Tables)	12 Months Ended
EARNINGS (LOSS) PER SHARE (Tables)	Dec. 31, 2023
Earnings Per Share [Abstract]
Schedule of Earnings (Loss) Per Share, Basic and Diluted	As the liquidation and dividend rights are identical for Class A and Class B common stock, the undistributed earnings are allocated on a proportional basis and the resulting net income (loss) per share attributable to common stockholders will, therefore, be the same for both Class A and Class B common stock on an individual or combined basis. Year Ended December 31, (In thousands, except per share data) 2023 2022 2021 Numerator: Net income (loss) attributable to Class A and Class B common stockholders $ 16,067 $ (59,574) (60,135) Denominator: Weighted-average shares in computing net income (loss) per share attributable to Class A and Class B common stockholders, basic and diluted 41,451 39,470 23,433 Effect of dilutive securities Founder awards where performance has been met 270 — Dilutive effect of stock options outstanding (1) 2,774 — — RSUs outstanding 2,027 — — Denominator for dilutive net income per common share - weighted-average shares 46,522 39,470 23,433 Basic income (loss) per common share $ 0.39 $ (1.51) $ (2.57) Diluted income (loss) per common share $ 0.35 $ (1.51) $ (2.57) ________________ (1) The Company had 3.0 million options outstanding as of December 31, 2023. The estimated dilutive effect is calculated as the number of shares expected to be issued upon vesting or exercise, adjusted for the strike price proceeds that are received by the Company and assumed to be used to repurchase shares of Duolingo common stock.
Schedule of Antidilutive Securities Excluded from Computation of Net Loss Per Share	The potential shares of common stock that were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive are as follows: Year Ended December 31, (In thousands) 2022 2021 Founder awards where performance has been met 180 180 Stock options outstanding 4,410 6,255 RSUs outstanding 2,036 730 Total 6,626 7,165

DESCRIPTION OF THE BUSINESS A_2

DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION (Details) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
	Jul. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) language shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($)	Jul. 29, 2021 USD ($) shares	Jul. 15, 2021 shares	Dec. 31, 2020 USD ($)
Business And Organization [Line Items]
Issuance of common stock in connection with the initial public offering, net of underwriting discounts and issuance costs \| $	$ 455,532	$ 0	$ 0	$ 426,191
Authorized (in shares)					19,074
Carrying value of convertible preferred stock \| $				$ 0	$ 182,609		$ 182,609
Number of languages, more than \| language		40
Common Class A
Business And Organization [Line Items]
Common stock, shares outstanding (in shares)		36,311	31,899
Common Class A \| IPO
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	5,872
Sale of stock, price per share (in usd per share) \| $ / shares	$ 102
Common Class A \| IPO \| Stockholders
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	1,406
Common Class A \| IPO \| Duolingo
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	4,466
Common Class A \| Over-Allotment Option
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	766
Common Class B
Business And Organization [Line Items]
Conversion ratio					1
Common stock, shares outstanding (in shares)		6,215	8,462
Common Class B \| Founders
Business And Organization [Line Items]
Common stock, shares outstanding (in shares)						6,930

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) shares in Thousands		1 Months Ended	12 Months Ended
	Mar. 10, 2021 USD ($)	Jun. 30, 2021 shares	Dec. 31, 2023 USD ($) sourceOfRevenue tranche reporting_unit shares	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Concentration Risk [Line Items]
Number of sources of revenue \| sourceOfRevenue			4
Number of days to take exam			21 days
Advertising costs			$ 52,969,000	$ 48,111,000	$ 42,964,000
Volunteer program, one-time payment to contributors	$ 4,220,000
Volunteer program, fees paid	$ 526,000
Compensation expense			$ 95,221,000	73,820,000	40,804,000
Number of reporting units \| reporting_unit			1
Impairment			$ 0	0	0
Research and development
Concentration Risk [Line Items]
Compensation expense			45,119,000	26,373,000	9,298,000
Sales and marketing
Concentration Risk [Line Items]
Compensation expense			3,908,000	2,540,000	881,000
General and administrative
Concentration Risk [Line Items]
Compensation expense			$ 46,139,000	44,869,000	30,617,000
RSUs outstanding
Concentration Risk [Line Items]
Number of vesting requirements \| tranche			2
Vesting period (in years)			4 years
Compensation expense					2,035,000
Equity instruments other than options, grants in period (in shares) \| shares			873
RSUs outstanding \| Research and development
Concentration Risk [Line Items]
Compensation expense					1,332,000
RSUs outstanding \| Sales and marketing
Concentration Risk [Line Items]
Compensation expense					210,000
RSUs outstanding \| General and administrative
Concentration Risk [Line Items]
Compensation expense					493,000
Founder awards where performance has been met
Concentration Risk [Line Items]
Compensation expense			$ 26,622,000	$ 30,997,000	$ 16,463,000
Founder awards where performance has been met \| Founders
Concentration Risk [Line Items]
Equity instruments other than options, grants in period (in shares) \| shares		1,800
Number of tranches \| tranche			10
Capitalized Software
Concentration Risk [Line Items]
Estimated useful life (in years)			3 years
Accounts Receivable \| Customer Concentration Risk \| Apple
Concentration Risk [Line Items]
Concentration risk (in percent)			65.20%	56.20%
Accounts Receivable \| Customer Concentration Risk \| Google
Concentration Risk [Line Items]
Concentration risk (in percent)			20.70%	27.50%
Accounts Receivable \| Customer Concentration Risk \| Stripe
Concentration Risk [Line Items]
Concentration risk (in percent)			10.70%
Revenue from Contract with Customer Benchmark \| Customer Concentration Risk \| Apple
Concentration Risk [Line Items]
Concentration risk (in percent)			58.50%	54.20%	50.50%
Revenue from Contract with Customer Benchmark \| Customer Concentration Risk \| Google
Concentration Risk [Line Items]
Concentration risk (in percent)			25.60%	28.10%	29%
Revenue from Contract with Customer Benchmark \| Customer Concentration Risk \| Stripe
Concentration Risk [Line Items]
Concentration risk (in percent)			12.10%		10.10%

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 747,610	$ 608,180
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	50,373	91,189
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 697,237	$ 516,991

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Useful Life (Details)	Dec. 31, 2023
Furniture, fixtures and equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	4 years
Furniture, fixtures and equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	6 years
Leasehold improvements \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	5 years
Leasehold improvements \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	7 years

ACQUISITION (Details)

ACQUISITION (Details) $ in Thousands		1 Months Ended	12 Months Ended
ACQUISITION (Details) $ in Thousands	Oct. 03, 2022 USD ($) term employee	Oct. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($)	Dec. 04, 2023
Asset Acquisition [Line Items]
Total undiscounted lease payments				$ 35,118
Sublease term (in months)	68 months
Sublease payments to be received			$ 358	$ 295
Building
Asset Acquisition [Line Items]
Lessee, operating lease, term of contract (in months)	68 months				73 months
Total undiscounted lease payments			750
Building \| Office Lease, Five Year Renewal Term
Asset Acquisition [Line Items]
Number of extension options \| term	1
Option to extend (in years)	5 years
Building \| Office Lease, Four Year Renewal Term
Asset Acquisition [Line Items]
Number of extension options \| term	1
Option to extend (in years)	4 years
Gunner Made LLC
Asset Acquisition [Line Items]
Number of design team members \| employee	15
Asset acquisition, consideration transferred	$ 4,500
Cash paid in asset acquisition	$ 4,000
Asset acquisition, amount held back until one year of continued service		$ 450
Continued service period (in years)	1 year
Acquisition costs			$ 50

REVENUE - Narrative (Details)

REVENUE - Narrative (Details)	12 Months Ended
REVENUE - Narrative (Details)	Dec. 31, 2023 sourceOfRevenue user	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Number of sources of revenue \| sourceOfRevenue	4
Number of users \| user	6
Number of hours to make certification decision (less than)	48 hours
Number of days to take exam	21 days
Expiration period to take exams (in years)	1 year
United States \| Revenue from Contract with Customer Benchmark \| Geographic Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (in percent)	45%	46%	44%
United Kingdom \| Revenue from Contract with Customer Benchmark \| Geographic Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk (in percent)	8%	9%	10%
Maximum
Disaggregation of Revenue [Line Items]
Subscription period (in years)	1 year

REVENUE - Disaggregation of Rev

REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	$ 531,109	$ 369,495	$ 250,772
Transferred over Time \| Subscription
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	404,684	273,507	180,698
Transferred over Time \| Advertising
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	49,858	44,731	38,501
Transferred over Time \| Duolingo English Test
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	41,212	32,718	24,658
Transferred over Time \| In-App Purchases
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	34,673	17,914	6,836
Transferred over Time \| Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	$ 682	$ 625	$ 79

REVENUE - Revenue by Geographic

REVENUE - Revenue by Geographic Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 531,109	$ 369,495	$ 250,772
United States
Disaggregation of Revenue [Line Items]
Revenues	238,759	168,320	109,163
United Kingdom
Disaggregation of Revenue [Line Items]
Revenues	42,118	31,539	25,163
Rest of World
Disaggregation of Revenue [Line Items]
Revenues	$ 250,232	$ 169,636	$ 116,446

REVENUE - Deferred Revenue Roll

REVENUE - Deferred Revenue Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Revenue from Contract with Customer, Liability [Roll Forward]
Beginning balance	$ 157,550	$ 98,267
Amount from beginning balance recognized into revenue	(157,550)	(98,267)
Recognition of deferred revenue	(287,429)	(199,130)
Deferral of revenue	536,621	356,680
Ending balance	$ 249,192	$ 157,550

PROPERTY and EQUIPMENT, net - S

PROPERTY and EQUIPMENT, net - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 24,060	$ 21,187
Less: accumulated depreciation	(12,268)	(8,218)
Total property and equipment, net	11,792	12,969
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	18,191	15,983
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 5,869	$ 5,204

PROPERTY and EQUIPMENT, net -_2

PROPERTY and EQUIPMENT, net - Summary of Depreciation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total	$ 4,100	$ 3,118	$ 2,033
Research and development
Property, Plant and Equipment [Line Items]
Total	1,650	1,500	260
Sales and marketing
Property, Plant and Equipment [Line Items]
Total	190	190	32
General and administrative
Property, Plant and Equipment [Line Items]
Total	$ 2,260	$ 1,428	$ 1,741

INTANGIBLE ASSETS AND GOODWIL_2

INTANGIBLE ASSETS AND GOODWILL - Capitalized Software (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Capitalized software	$ 26,895	$ 16,809
Other intangible assets	117	18
Total intangible assets	27,012	16,827
Less: accumulated amortization	(11,017)	(8,330)
Intangible assets, net	$ 15,995	$ 8,497

INTANGIBLE ASSETS AND GOODWIL_3

INTANGIBLE ASSETS AND GOODWILL - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Capitalized Computer Software, Additions	$ 5,665
Goodwill	4,050	$ 4,050
Goodwill, tax deductible amount	$ 3,983	$ 3,713

INTANGIBLE ASSETS AND GOODWIL_4

INTANGIBLE ASSETS AND GOODWILL - Schedule of Capitalized Software Amortization Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Amortization of capitalized computer software	$ 2,995	$ 1,752	$ 693
Cost of revenues
Finite-Lived Intangible Assets [Line Items]
Amortization of capitalized computer software	2,020	870	0
Sales and marketing
Finite-Lived Intangible Assets [Line Items]
Amortization of capitalized computer software	$ 975	$ 882	$ 693

LEASES - Narrative (Details)

LEASES - Narrative (Details) $ in Thousands	Oct. 03, 2022 term	Jan. 10, 2030 USD ($)	Dec. 31, 2023 USD ($)	Dec. 18, 2023 USD ($) ft² month	Dec. 04, 2023	Dec. 31, 2022 USD ($)
Lessee, Lease, Description [Line Items]
Renewal term (in years)			5 years
Sublease term (in months)	68 months
Sublease payments to be received			$ 295			$ 358
Obligations under current leases			3,944			$ 4,903
Total undiscounted lease payments			$ 35,118
Operating lease, liability, current, statement of financial position, [extensible enumeration]			Accrued expenses and other current liabilities			Accrued expenses and other current liabilities
Long-term obligation under operating leases			$ 21,094			$ 23,503
Area of office building \| ft²				85,666
Initial base rent per month				$ 442
Term before rent increase				6 years
Number of months commencement of the sub-sublease \| month				20
Restricted cash			2,735			0
Forecast
Lessee, Lease, Description [Line Items]
Initial base rent per month		$ 478
Office Lease, Additional Extension Term
Lessee, Lease, Description [Line Items]
Total undiscounted lease payments			$ 1,380
Building
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract (in months)	68 months				73 months
Total undiscounted lease payments						$ 750
Building \| Office Lease, Five Year Renewal Term
Lessee, Lease, Description [Line Items]
Number of extension options \| term	1
Option to extend (in years)	5 years
Building \| Office Lease, Four Year Renewal Term
Lessee, Lease, Description [Line Items]
Number of extension options \| term	1
Option to extend (in years)	4 years

LEASES - Components of Lease Co

LEASES - Components of Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating lease cost	$ 7,459	$ 7,076	$ 1,919
Short term lease cost	48	125	1,266
Variable lease cost	252	63	28
Total lease cost	7,759	7,264	3,213
Cash paid for amounts included in the measurement of lease liabilities	7,512	5,168	1,819
Right-of-use assets obtained in exchange for new operating lease liabilities	0	909	22,274
Right of use assets disposed or adjusted, modifying operating leases liabilities	2,024	(1,586)	(235)
Gain from termination of leases	$ 0	$ 0	$ 31
Weighted-average remaining lease term	9 years	9 years	9 years
Weighted-average discount rate	7.38%	6.92%	5.77%

LEASES - Future Minimum Rental

LEASES - Future Minimum Rental Payment (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Leases [Abstract]
2024	$ 5,607
2025	3,386
2026	3,399
2027	3,463
2028	3,528
Thereafter	15,735
Total undiscounted lease payments	35,118
Present value adjustment	(10,080)
Operating lease liabilities	$ 25,038

INCOME TAXES - Income Before In

INCOME TAXES - Income Before Income Tax, Domestic and Foreign (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Domestic	$ 16,501	$ (60,099)	$ (59,737)
Foreign	1,276	1,463	(221)
Income (loss) before income taxes	$ 17,777	$ (58,636)	$ (59,958)

INCOME TAXES - Provision of Inc

INCOME TAXES - Provision of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current Federal, State and Local, Tax Expense (Benefit) [Abstract]
Federal	$ 895	$ 302	$ 0
State	607	327	80
Foreign	341	524	97
Current Income Tax Expense (Benefit), Total	1,843	1,153	177
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	0	0	0
State	0	0	0
Foreign	(133)	(215)	0
Total	(133)	(215)	0
Provision for income taxes	$ 1,710	$ 938	$ 177

INCOME TAXES - Effective Income

INCOME TAXES - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Expected income tax expense at federal statutory rate	21%	21%	21%
State taxes, net of Federal income tax effect	(35.10%)	6.70%	6.50%
Section 162(m) limitation	56.50%	(15.20%)	(13.50%)
Equity compensation	(208.40%)	28.40%	53.80%
Meals and entertainment	5.60%	(1.20%)	(0.50%)
Foreign-Derived Intangible Income deduction	(13.40%)	0%	0%
Other permanent adjustments	2.20%	0.30%	0%
Research and development credit	(76.40%)	11.70%	15.90%
Valuation allowance	257.60%	(53.30%)	(83.50%)
Effective income tax rate	9.60%	(1.60%)	(0.30%)

INCOME TAXES - Deferred Tax Ass

INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 15,533	$ 42,861
Stock-based compensation	5,207	3,605
Research and development credits	38,146	22,386
Lease liability	5,739	6,487
Section 174 research and development capitalization	102,055	42,429
Marketing and advertising	766	633
Sales tax / Value added tax ("VAT") reserve	397	210
Other deferred tax assets	65	140
Valuation allowance	(156,870)	(108,504)	$ (76,293)
Total deferred tax assets	11,038	10,247
ROU asset	(4,354)	(5,122)
Property and equipment	(2,164)	(2,569)
Capitalized software	(3,716)	(1,913)
Other deferred tax liabilities	(38)	(10)
Total deferred tax liabilities	(10,272)	(9,614)
Net deferred taxes	$ 766	$ 633

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
INCOME TAXES - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Tax Credit Carryforward [Line Items]
Increase in valuation allowance	$ 48,366,000
Unrecognized tax benefits	0	$ 0	$ 0
General Business Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Business credits	38,146,000
Federal
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	48,866,000
State
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	$ 71,422,000

INCOME TAXES - Valuation Allowa

INCOME TAXES - Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Deferred Tax Assets, Valuation Allowance [Roll Forward]
Beginning balance	$ (108,504)	$ (76,293)
Valuation allowances established	(48,366)	(32,211)
Release of valuation allowances	0	0
Ending balance	$ (156,870)	$ (108,504)

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) $ / shares in Units, $ in Thousands			1 Months Ended		12 Months Ended
	Jan. 01, 2024 shares	Jan. 01, 2022	Jun. 30, 2021 day tranche $ / shares shares	Feb. 28, 2021 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) tranche	Jul. 30, 2021 $ / shares	Jul. 26, 2021 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares					0	0
Aggregate intrinsic value, exercised					$ 192,456	$ 140,884	$ 194,513
Compensation expense					95,221	73,820	40,804
Unrecognized compensation cost, options					1,393
Unrecognized compensation cost					201,826
Closing trading price, specified calendar day \| day			60
Fair market value of share price (in usd per share) \| $ / shares				$ 38.08
Payments for repurchase of stock options					$ 0	0	7,335
Options repurchased							7,335
Common stock repurchased and retired							868
Additional Paid-In Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock repurchased and retired							868
Tender Offer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense				$ 5,275
Sale of stock, percentage sold, maximum				10%
Sale of stock, price per share (in usd per share) \| $ / shares				$ 59.77
Payments for repurchase of stock options				$ 13,479
Stock returned during the period (in shares) \| shares				220,000
Common stock repurchased and retired (in shares) \| shares				23,000
Common stock repurchased and retired				$ 868
Tender Offer \| Additional Paid-In Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options repurchased				$ 7,335
Stock options outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, weighted-average period of recognition (in years)					7 months
Number of options available for grant (in shares) \| shares					9,404,000
RSUs outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)					4 years
Compensation expense							2,035
Unrecognized compensation cost, weighted-average period of recognition (in years)					3 years
Unrecognized compensation expense, excluding options					$ 200,433
Equity instruments other than options, grants in period (in shares) \| shares					873,000
Performance Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense					$ 26,622	$ 30,997	16,463
Unrecognized compensation expense, excluding options					36,735
Performance Based RSUs \| IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense							$ 5,574
Performance Based RSUs \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award service period (in years)			3 years 6 months 29 days
Performance Based RSUs \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award service period (in years)			5 years 11 months 1 day
Performance Based RSUs \| Founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, excluding options					$ 110,817
Equity instruments other than options, grants in period (in shares) \| shares			1,800,000
Settlement period after vesting (in years)			1 year
Award vesting percentage (in percent)			25%
Number of tranches \| tranche			10
Award service period (in years)			10 years
Performance Based RSUs \| Founders \| Tranche One and Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of tranches \| tranche							2
Release of performance stock units (in shares) \| shares					180,000
Shares disbursed to founders in net-share settlement (in shares) \| shares					96,000
Shares withheld for taxes (in shares) \| shares					84,000
Performance Based RSUs \| Share-Based Payment Arrangement, Founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in usd per share) \| $ / shares			$ 61.56
Common Class A \| IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock, price per share (in usd per share) \| $ / shares								$ 102
2021 Plan \| Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares) \| shares									7,946,000
Share-based compensation, shares outstanding increase, maximum amount (in percent)		5%
2021 Plan \| Common Class A \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized (in shares) \| shares	2,126,000
Employee Stock Purchase Plan \| Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares) \| shares									1,119,000
2011 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)					4 years
Share-based compensation, term of award (in years)					10 years
Granted (in shares) \| shares					0

STOCK-BASED COMPENSATION - Stoc

STOCK-BASED COMPENSATION - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of options
Options outstanding, beginning balance (in shares)	4,410,000
Granted (in shares)	0	0
Exercised (in shares)	(1,396,000)
Forfeited and expired (in shares)	(29,000)
Options outstanding, ending balance (in shares)	2,985,000	4,410,000
Number of options exercisable (in shares)	2,817,000
Weighted- average exercise price
Outstanding, beginning balance (in usd per share)	$ 14.04
Granted (in usd per share)
Exercised (in usd per share)	9.76
Forfeited and expired (in usd per share)	14.09
Outstanding, ending balance (in usd per share)	16.04	$ 14.04
Weighted average exercise price, options exercisable (in usd per share)	$ 15.54
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual term (in years), outstanding	5 years 7 months 6 days	6 years 3 months
Weighted average remaining contractual term (in years), exercisable	5 years 6 months 14 days
Aggregate intrinsic value, outstanding	$ 629,865	$ 251,832
Aggregate intrinsic value, exercisable	$ 594,157

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Payment Pricing Model (Details)	12 Months Ended
	Dec. 31, 2021 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	1.04%
Risk-free interest rate, maximum	1.14%
Expected life	5 years 10 months 24 days
Expected volatility, minimum	48.90%
Expected volatility, maximum	49.12%
Dividend yield	0%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock (in usd per share)	$ 38.08
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock (in usd per share)	$ 52.80

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Restricted Stock Unit Activity (Details) - RSUs outstanding - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Restricted stock units
Beginning balance (in shares)	2,027	2,036
Granted (in shares)	873
Released (in shares)	(673)
Forfeited (in shares)	(209)
Ending balance (in shares)	2,027
Weighted- average grant date fair value per share
Beginning balance (in usd per share)	$ 85.74
Granted (in usd per share)	138.99
Released (in usd per share)	89.58
Forfeited (in usd per share)	96.23
Ending balance (in usd per share)	$ 106.32

STOCK-BASED COMPENSATION - Sc_3

STOCK-BASED COMPENSATION - Schedule of Payment Award (Details) - RSUs outstanding shares in Thousands	Jun. 30, 2021 $ / shares shares
1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 127.50
Number of RSUs Eligible to Vest (in shares) \| shares	90
2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 153
Number of RSUs Eligible to Vest (in shares) \| shares	90
3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 178.50
Number of RSUs Eligible to Vest (in shares) \| shares	90
4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 204
Number of RSUs Eligible to Vest (in shares) \| shares	180
5
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 255
Number of RSUs Eligible to Vest (in shares) \| shares	180
6
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 306
Number of RSUs Eligible to Vest (in shares) \| shares	180
7
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 357
Number of RSUs Eligible to Vest (in shares) \| shares	180
8
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 408
Number of RSUs Eligible to Vest (in shares) \| shares	180
9
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 612
Number of RSUs Eligible to Vest (in shares) \| shares	270
10
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) \| $ / shares	$ 816
Number of RSUs Eligible to Vest (in shares) \| shares	360

STOCK-BASED COMPENSATION - Sc_4

STOCK-BASED COMPENSATION - Schedule of Weighted Average Pricing Model (Details) - $ / shares		12 Months Ended
	Jun. 28, 2021	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life		5 years 10 months 24 days
Dividend yield		0%
Founder awards where performance has been met
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.48%
Expected life	9 years 11 months 23 days
Expected volatility	51.67%
Dividend yield	0%
Fair value of common stock (in usd per share)	$ 95

STOCK-BASED COMPENSATION - Sc_5

STOCK-BASED COMPENSATION - Schedule of Income Statement Location for Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 95,221	$ 73,820	$ 40,804
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	55	38	8
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	45,119	26,373	9,298
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	3,908	2,540	881
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 46,139	$ 44,869	$ 30,617

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 18, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Period of letter of credit	6 months
Initial base rent per month		$ 442
Letters of credit	$ 2,656
Percentage of letter of credit	103%
Restricted cash	$ 2,735		$ 0

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Other Liabilities Disclosure [Abstract]
Marketing-related accruals	$ 4,732	$ 3,464
Employee-related costs	4,494	4,233
Sales and VAT tax accrual	4,365	2,396
Obligations under current leases	3,944	4,903
Hosting costs	3,079	2,102
Other	4,317	4,872
Total	$ 24,931	$ 21,970
Operating lease, liability, current, statement of financial position, [extensible enumeration]	Total	Total

EMPLOYEE BENEFIT PLAN (Details)

EMPLOYEE BENEFIT PLAN (Details) - USD ($)	12 Months Ended
EMPLOYEE BENEFIT PLAN (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, contributions by employer	$ 5,908,000	$ 4,624,000	$ 3,438,000
Defined contribution plan, employer discretionary contribution amount	$ 0	$ 0	$ 0
First 4% of Employee Elective Deferral
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match (in percent)	100%
Employer matching contribution, percent of employees' gross pay (in percent)	4%
Next 2% of Employee Elective Deferral
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match (in percent)	50%
Employer matching contribution, percent of employees' gross pay (in percent)	2%

EARNINGS (LOSS) PER SHARE - Nar

EARNINGS (LOSS) PER SHARE - Narrative (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2023 votePerShare	Dec. 31, 2022 shares	Dec. 31, 2021 shares
Performance Based RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Founder awards where performance not met (in shares) \| shares		1,620	1,620
Common Class A
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Voting rights, per share	1
Common Class B
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Voting rights, per share	20

EARNINGS (LOSS) PER SHARE - Sch

EARNINGS (LOSS) PER SHARE - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net income (loss) attributable to Class A and Class B common stockholders	$ 16,067	$ (59,574)	$ (60,135)
Denominator:
Weighted-average shares in computing net income (loss) per share attributable to Class A and Class B common stockholders, basic (in shares)			23,433
Weighted-average shares in computing net income (loss) per share attributable to Class A and Class B common stockholders, diluted (in shares)	46,522	39,470	23,433
Effect of dilutive securities
Basic loss per common share (in usd per share)	$ 0.39	$ (1.51)	$ (2.57)
Diluted loss per common share (in usd per share)	$ 0.35	$ (1.51)	$ (2.57)
Options outstanding (in shares)	2,985	4,410
Founder awards where performance has been met
Effect of dilutive securities
Stock options and RSUs outstanding (in shares)	270	0
Stock options outstanding
Effect of dilutive securities
Stock options and RSUs outstanding (in shares)	2,774	0	0
RSUs outstanding
Effect of dilutive securities
Stock options and RSUs outstanding (in shares)	2,027	0	0
Class A and Class B Common Stock
Denominator:
Weighted-average shares in computing net income (loss) per share attributable to Class A and Class B common stockholders, basic (in shares)	41,451	39,470
Weighted-average shares in computing net income (loss) per share attributable to Class A and Class B common stockholders, diluted (in shares)	41,451	39,470

EARNINGS (LOSS) PER SHARE - S_2

EARNINGS (LOSS) PER SHARE - Schedule of Antidilutive Securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	6,626	7,165
Founder awards where performance has been met
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	180	180
Stock options outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	4,410	6,255
RSUs outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	2,036	730

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($) $ in Thousands	Feb. 28, 2024	Dec. 31, 2023
Subsequent Event [Line Items]
Expected lease payments		$ 35,118
Subsequent Event
Subsequent Event [Line Items]
Lessee, operating lease, term of contract (in months)	63 months
Expected lease payments	$ 1,728