Costco Wholesale (COST) 424B5Prospectus supplement for primary offering

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-237699

CALCULATION OF REGISTRATION FEE

PROSPECTUS SUPPLEMENT

(To Prospectus dated April 15, 2020)

$4,000,000,000

$1,250,000,000 1.375% Senior Notes due 2027

$1,750,000,000 1.600% Senior Notes due 2030

$1,000,000,000 1.750% Senior Notes due 2032

This is an offering of an aggregate of $1,250,000,000 principal amount of 1.375% Senior Notes due 2027, which we refer to as the “2027 Notes”, an aggregate of $1,750,000,000 principal amount of 1.600% Senior Notes due2030, which we refer to as the “2030 Notes” and an aggregate of $1,000,000,000 principal amount of 1.750% Senior Notes due 2032, which we refer to as the “2032 Notes”. We refer to the 2027 Notes, the 2030 Notes and the 2032 Notes together as the “notes”.

We will pay interest on the 2027 Notes semi-annually in arrears on June 20 and December 20 of each year, beginning on December 20, 2020. We will pay interest on the 2030 Notes and the 2032 Notes semi-annually in arrears on April 20 and October 20 of each year, beginning on October 20, 2020. The 2027 Notes will bear interest at a rate of 1.375% per year and will mature on June 20, 2027. The 2030 Notes will bear interest at a rate of 1.600% per year and will mature on April 20, 2030. The 2032 Notes will bear interest at a rate of 1.750% per year and will mature on April 20, 2032. We may redeem any of the notes at any time by paying the greater of the principal amount of the notes or a “make-whole” amount, plus, in each case, accrued and unpaid interest.

The notes will be our unsecured and unsubordinated obligations ranking equally with our other outstanding unsecured and unsubordinated indebtedness from time to time outstanding.

For a more detailed description of the notes, See “Description of the Notes” beginning onpage S-10 of this prospectus supplement.

See “Risk Factors” on pageS-6 for a discussion of certain risks that should be considered in connection with an investment in the notes.

Delivery of the notes will be made in book-entry form only through the facilities of The Depository Trust Company and its direct and indirect participants on or about April 20, 2020, against payment therefor in immediately available funds.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus to which it relates is truthful or complete. Any representation to the contrary is a criminal offense.

The notes are new issues of securities with no established trading market. We do not intend to apply to list the notes on any securities exchange or to quote the notes on any automated dealer system.

Joint Book-Running Managers

US Bancorp

HSBC

Drexel Hamilton

Guzman and Company

April 16, 2020.

We have not, and the underwriters have not, authorized any dealer, salesperson or other person to give any information or to make any representation other than those contained or incorporated by reference in this prospectus supplement and the accompanying prospectus. You must not rely upon any information or representation not contained or incorporated by reference in this prospectus supplement or the accompanying prospectus. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell or the solicitation of an offer to buy any securities other than the registered securities to which they relate, nor do this prospectus supplement and the accompanying prospectus constitute an offer to sell or the solicitation of an offer to buy securities in any jurisdiction to any person to whom it is unlawful to make such offer or solicitation in such jurisdiction. The information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus is accurate as of the dates on their respective covers. Our business, financial condition, results of operations and prospects may have changed since those dates. When we deliver this prospectus supplement and the accompanying prospectus or make a sale pursuant to this prospectus supplement and the accompanying prospectus, we are not implying that the information is current as of the date of the delivery or sale.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS SUPPLEMENT

This document has two parts. The first part consists of this prospectus supplement, which describes the specific terms of this offering and the notes offered. The second part, the accompanying prospectus, provides more general information, some of which may not apply to this offering. If the description of the offering varies between this prospectus supplement and the accompanying prospectus, you should rely on the information in this prospectus supplement. To the extent that information in this prospectus supplement or any related free writing prospectus is inconsistent with the information incorporated by reference in this prospectus supplement, the information in such document incorporated by reference is superseded by the information in the prospectus supplement or free writing prospectus, as the case may be. You should read this prospectus supplement and the accompanying prospectus, the documents incorporated by reference into this prospectus supplement and the accompanying prospectus and any related free writing prospectus when making your investment decision. You should also read and consider the information in the documents we have referred you in the section of the accompanying prospectus entitled “Where You Can Find Additional Information.”

Unless otherwise indicated, all references in this prospectus supplement to “we,” “us,” “our” or “Costco” refer to Costco Wholesale Corporation and its consolidated subsidiaries.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference contain certain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended. They include statements that address activities, events, conditions or developments that we expect or anticipate may occur in the future and may relate to such matters as sales growth, changes in comparable sales, cannibalization of existing locations by new openings, price or fee changes, earnings performance, earnings per share, stock-based compensation expense, warehouse openings and closures, capital spending, the effect of accounting standards, future financial reporting, financing, margins, return on invested capital, strategic direction, expense controls, membership renewal rates, shopping frequency, litigation, and the demand for our products and services. Forward-looking statements may also be identified because they contain words such as “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “likely,” “may,” “might,” “plan,” “potential,” “predict,” “project,” “seek,” “should,” “target,” “will,” “would,” or similar expressions and the negatives of those terms.

Forward-looking statements provide our expectations or predictions of future conditions, events or results. They are not guarantees of future performance. By their nature forward-looking statements involve risks and uncertainties. These statements speak only as of the date they are made. We do not undertake to update forward-looking statements to reflect the impact of circumstances or events that arise after the date the forward-looking statements were made, except as may be required by law. There are a number of factors, many of which are beyond our control, that may cause actual events, results, or performance to differ materially from those described in the forward-looking statements. These risks and uncertainties include, but are not limited to, domestic and international economic conditions, including exchange rates, the effects of competition and regulation, uncertainties in the financial markets, consumer and small business spending patterns and debt levels, breaches of security or privacy of member or business information, conditions affecting the acquisition, development, ownership or use of real estate, capital spending, actions of vendors, rising costs associated with employees (generally including health care costs), energy and certain commodities, geopolitical conditions (including tariffs), the ability to maintain effective internal control over financing reports, the effects of theCOVID-19 coronavirus outbreak, including among others, the duration of the pandemic, the unknown long-term economic impact, reduced customer shopping due to illness, travel restrictions or financial hardship, shifts in demand away from discretionary or higher priced products to lower priced products, reduced workforce due to illness, quarantine, or government mandates, temporary store closures due to reduced workforces or government mandates, or supply chain disruptions, and other factors described in Part I, Item 1A of our most recent Annual Report on Form10-K in the section entitled “Risk Factors,” in Part II, Item 1A of our most recent Quarterly Report on Form10-Q in the section entitled “Risk Factors” and as may be included from time to time in our reports filed with the SEC.

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RISK FACTORS

Investing in the notes involves risks. Before making a decision to invest in the notes, you should carefully consider the risks described under “Risk Factors” in Item 1A of our Annual Report on Form10-K for the fiscal year ended September 1, 2019, which is incorporated by reference in the accompanying prospectus, as well as the risks set forth below. See “Where You Can Find More Information” in the accompanying prospectus.

We and our subsidiaries may be able to incur substantially more debt, which could exacerbate the risks described in this prospectus supplement.

We and our subsidiaries may be able to incur substantial additional indebtedness in the future. We will not be restricted under the terms of the notes or the indenture pursuant to which the notes are to be issued from incurring additional indebtedness, including secured debt. In addition, the notes do not require us to achieve or maintain any minimum financial results relating to our financial condition or results of operations. Because we are not limited by the terms of the notes, we may recapitalize, incur additional debt and take a number of other actions that could have the effect of diminishing our ability to make payments on the notes when due or otherwise adversely affecting the value of the notes. In addition, we are not restricted from repurchasing common stock by the terms of the notes.

Active trading markets may not develop for the notes.

The notes are new issues of securities with no established trading markets. We do not intend to apply for listing of the notes on any securities exchange. We cannot assure you that trading markets for the notes will develop or of the ability of holders of the notes to sell their notes or of the prices at which holders may be able to sell their notes. The underwriters have advised us that they currently intend to make a market in each series of the notes. However, the underwriters are not obligated to do so, and any market-making with respect to the notes may be discontinued, in their sole discretion, at any time without notice. If no active trading markets develop, you may be unable to resell the notes at any price or at their fair market value.

If trading markets do develop, changes in our ratings or the financial markets could adversely affect the market prices of the notes.

Any market prices of the notes will depend on many factors, including, among others, the following:

The condition of the financial markets and prevailing interest rates have fluctuated in the past and are likely to fluctuate in the future, which could have an adverse effect on any market prices of the notes.

Rating agencies continually review the ratings they have assigned to companies and debt securities. Negative changes in the ratings assigned to us or our debt securities could have an adverse effect on the market prices of the notes.

TheCOVID-19 coronavirus outbreak is adversely affecting many aspects of our business functions, financial condition and results of operations.

TheCOVID-19 coronavirus outbreak has resulted in widespread and continuing impacts on the global economy and on our employees, members, suppliers, and other people and entities with which we do business. There is considerable uncertainty regarding the extent to which the coronavirus will continue to spread and the extent and duration of measures to try to contain the virus, such as travel bans and restrictions, quarantines,

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shelter-in-place orders, and business and government shutdowns. Many government subdivisions have imposed restrictions on the operation of our membership warehouses, including limiting the number of members who may enter at one time and preventing the sales of certain categories of merchandise. We are taking temporary precautionary measures intended to help minimize the risk of the virus to our employees, including temporarily requiring some employees to work remotely and suspending allnon-essential travel for our employees, which could negatively affect our business. To reward our employees for exemplary service in difficult times we have temporarily increased compensation levels and otherwise incurred increased spending for wages and benefits, including overtime pay. The outbreak and any preventative or protective actions that governments or we may take in respect of this coronavirus are likely to result in a period of business disruption, reduced member traffic and reduced sales in certain merchandise categories, and increased operating expenses, which we currently estimate will exceed $250 million for the fiscal quarter ending May 10, 2020. The extent to which the coronavirus impacts our results and financial condition will depend on future developments, which are highly uncertain and cannot be predicted, including new information that may emerge concerning the severity of the coronavirus and the actions to contain and treat its impacts, among others.

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USE OF PROCEEDS

We estimate that the net proceeds to us from this offering will be approximately $3,970 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by us. We intend to use the net proceeds of this offering for the following purposes:

We may temporarily invest the net proceeds pending use for these purposes in short-term investments, including, but not limited to, marketable debt securities.

To the extent that the underwriters or their affiliates own any of our 2.15% Senior Notes due 2021 or 2.25% Senior Notes due 2022, they may receive a portion of the net proceeds that we use from this offering to repay their 2.15% Senior Notes due 2021 or 2.25% Senior Notes due 2022.

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CAPITALIZATION

The following sets forth our capitalization on a consolidated basis at February 16, 2020. We have presented our capitalization on both an actual and an as adjusted basis to reflect the issuance and sale of the notes offered hereby and the application of the net proceeds from the issuance and sale of the notes, including the repayment, at or prior to maturity, of all of our 2.15% Senior Notes due 2021 and all of our 2.25% Senior Notes due 2022 (excluding estimated make-whole premiums of approximately $33.6 million in the aggregate). See “Use of Proceeds.” You should read the following table together with our consolidated financial statements and the accompanying notes to those statements, and the information set forth under “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in our Annual Report onForm 10-K for the fiscal year ended September 1, 2019, and in our Quarterly Reports onForm 10-Q for the fiscal quarter ended November 24, 2019 and for the fiscal quarter ended February 16, 2020, which are incorporated by reference in the accompanying prospectus. See “Where You Can Find More Information” in the accompanying prospectus.

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DESCRIPTION OF THE NOTES

We are offering $1,250,000,000 aggregate principal amount of our 1.375% Senior Notes due 2027 (the “2027 Notes”), $1,750,000,000 aggregate principal amount of our 1.600% Senior Notes due 2030 (the “2030 Notes”) and $1,000,000,000 aggregate principal amount of our 1.750% Senior Notes due 2032 (the “2032 Notes” and, collectively with the 2027 Notes and the 2030 Notes, the “notes”). The 2027 Notes, 2030 Notes and 2032 Notes will each constitute a series of senior debt securities described in the accompanying prospectus. This description supplements, and to the extent inconsistent therewith, replaces the descriptions of the general terms and provisions contained in “Description of Debt Securities” in the accompanying prospectus.

The 2027 Notes

The 2027 Notes will mature on June 20, 2027, and will bear interest at 1.375% per annum from April 20, 2020, or from the most recent date to which interest has been paid or provided for, payable semi-annually in arrears to holders of record at the close of business on the June 5 and December 5 immediately preceding the interest payment date on June 20 and December 20 of each year, commencing December 20, 2020.

The 2030 Notes

The 2030 Notes will mature on April 20, 2030, and will bear interest at 1.600% per annum from April 20, 2020, or from the most recent date to which interest has been paid or provided for, payable semi-annually in arrears to holders of record at the close of business on the April 5 and October 5 immediately preceding the interest payment date on April 20 and October 20 of each year, commencing October 20, 2020.

The 2032 Notes

The 2032 Notes will mature on April 20, 2032, and will bear interest at 1.750% per annum from April 20, 2020, or from the most recent date to which interest has been paid or provided for, payable semi-annually in arrears to holders of record at the close of business on the April 5 and October 5 immediately preceding the interest payment date on April 20 and October 20 of each year, commencing October 20, 2020.

General

If any interest payment date, date of redemption or the maturity date of any of the notes is not a business day, then payment of principal and interest will be made on the next succeeding business day. No interest will accrue on the amount so payable for the period from the interest payment date, redemption date or maturity date, as the case may be, to the date payment is made. Interest will be computed on the basis of a360-day year of twelve30-day months.

The notes do not contain any sinking fund provisions.

The notes will be issued only in registered form without coupons, in denominations of $2,000 or integral multiples of $1,000 in excess thereof. No service charge will be made for any registration of transfer or any exchange of notes, but we may require payment of a sum sufficient to cover any transfer tax or similar governmental charge payable in connection therewith.

The notes will be our unsecured and unsubordinated obligations ranking equally with our other outstanding unsecured and unsubordinated indebtedness from time to time outstanding. See “Description of Debt Securities” in the accompanying prospectus for a description of the rights under our debt securities, including the notes, under the indenture. In addition to the notes, we may issue other series of debt securities under the indenture. There is no limit on the total aggregate principal amount of debt securities that we can issue under the indenture.

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We could enter into various transactions that could increase the amount of our outstanding indebtedness, or adversely affect our capital structure or credit ratings, or otherwise adversely affect holders of the notes. The indenture governing the notes does not generally prevent us from entering into a variety of acquisition, refinancing, recapitalization or other highly leveraged transactions. As a result, we could enter into any transaction even though the transaction could increase the total amount of our outstanding indebtedness, adversely affect our capital structure or credit ratings, or otherwise adversely affect the value of and holders of the notes.

We are obligated to purchase debt securities upon a change in control

In the event of a Change of Control Triggering Event, unless we have exercised our right to redeem the notes as described below, you will have the right, at your option, subject to the terms and conditions of the indenture, to require us to purchase for cash any or all of your notes in integral multiples of $1,000 original principal amount. We will purchase the notes at a price equal to 101% of the principal amount of the notes to be purchased plus accrued and unpaid interest to, but excluding, the change in control purchase date, if any (the “Change of Control Payment”).

Within 15 days following any Change of Control Triggering Event, we must mail a written notice to the trustee and every holder of notes describing the transaction or transactions that constitute the Change of Control Triggering Event. The notice must also be published at least once in an authorized newspaper, as defined in the indenture, and must state:

On the Change of Control Payment Date, we will be obligated, to the extent lawful, to:

We will not purchase any notes if there has occurred and is continuing at the payment date an event of default under the indenture, other than default in payment of the purchase price payable for the notes upon a Change of Control Triggering Event. In connection with any purchase of notes after a Change of Control Triggering Event, we will comply with all federal and state securities laws, including, specifically, Rule13e-4, if applicable, under the Securities Exchange Act of 1934, as amended, and any related Schedule13E-4 required to be submitted under that rule.

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For purposes of the foregoing discussion of a repurchase at the option of holders, the following definitions are applicable:

“Below Investment Grade Rating Event” means the notes are rated below an Investment Grade Rating by each of the Rating Agencies (as defined below) on any date from the date of the public notice of an arrangement that would, if consummated, result in a Change of Control until the end of the60-day period following public notice of the occurrence of the Change of Control (which60-day period shall be extended so long as the rating of the notes is under publicly announced consideration for possible downgrade by any of the Rating Agencies).

“Change of Control” means the occurrence of any of the following: (1) any event requiring the filing of any report under or in response to Schedule 13D or14D-1 pursuant to the Securities Exchange Act of 1934, as amended, disclosing beneficial ownership of either 50% or more of our common stock then outstanding or 50% or more of the voting power of our voting stock then outstanding; (2) the completion of any sale, transfer, lease, or conveyance of our properties and assets substantially as an entirety to any “person” or “persons” that is not our “subsidiary,” as those terms are defined in the indenture; (3) the completion of a consolidation or merger of Costco with or into any other person or entity in a transaction in which either we are not the sole surviving corporation or our common stock existing before the transaction is converted into cash, securities or other property and in which those exchanging our common stock do not, as a result of the transaction, receive either 75% or more of the survivor’s common stock or 75% or more of the voting power of the survivor’s voting stock or (4) the first day on which a majority of the members of our Board of Directors are not Continuing Directors.

“Change of Control Triggering Event” means the occurrence of both a Change of Control and a Below Investment Grade Rating Event.

“Continuing Directors” means, as of any date of determination, any member of our Board of Directors who (1) was a member of our Board of Directors on April 15, 2020; or (2) was nominated for election or elected to our Board of Directors with the approval of a majority of the Continuing Directors who were members of our Board of Directors at the time of such nomination or election (either by a specific vote or by approval of our proxy statement in which such member was named as a nominee for election as a director, without objection to such nomination).

“Investment Grade Rating” means a rating equal to or higher than Baa3 (or the equivalent) by Moody’s and BBB– (or the equivalent) by S&P.

“Moody’s” means Moody’s Investors Service, Inc.

“Rating Agencies” means (1) each of Moody’s and S&P; and (2) if either of Moody’s or S&P ceases to rate the notes or fails to make a rating of the notes publicly available for reasons outside of our control, a “nationally recognized statistical rating organization” within the meaning of Section 3(a)(62) of the Securities Exchange Act of 1934, as amended, selected by us (as certified by a resolution of our Board of Directors) as a replacement agency for Moody’s or S&P, or both of them, as the case may be.

“S&P” means Standard & Poor’s Ratings Services, a division of The McGraw-Hill Companies, Inc.

Additional notes

We may, without prior notice to or the consent of the holders of the notes, create and issue additional notes ranking equally with any series of the notes in all respects (except for the issue date, price to public and, if applicable, the initial interest payment date), so that the additional notes shall be consolidated and form a single series with such notes and shall have the same terms as to status or otherwise as such notes, provided that the additional notes will have a different CUSIP number from the notes if the additional notes are not fungible with the notes for U.S. federal income tax purposes. No additional notes may be issued if an event of default has occurred and is continuing with respect to such series of notes.

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Optional redemption

At any time prior to April 20, 2027 (in the case of the 2027 Notes), January 20, 2030 (in the case of the 2030 Notes) and January 20, 2032 (in the case of the 2032 Notes), we will have the right at our option, at any time and from time to time, to redeem all or any portion of the notes on not less than 30 nor more than 60 days’ prior notice mailed to the holders of the notes to be redeemed. The notes will be redeemable at a redemption price, as calculated by us, equal to the greater of (1) 100% of the principal amount of the notes to be redeemed or (2) the sum of the present values of the remaining scheduled payments of principal and interest on the notes to be redeemed that would be due after the related redemption date but for the redemption (except that, if the redemption date is not an interest payment date, the amount of the next succeeding scheduled interest payment will be reduced by the amount of interest accrued thereon to the redemption date), discounted to the redemption date on a semiannual basis (assuming a360-day year consisting of twelve30-day months). The discount rate for the 2027 Notes will be the Treasury Rate plus 15 basis points, the discount rate for the 2030 Notes will be the Treasury Rate plus 15 basis points and the discount rate for the 2032 Notes will be the Treasury Rate plus 20 basis points.

At any time on or after April 20, 2027 (in the case of the 2027 Notes), January 20, 2030 (in the case of the 2030 Notes) and January 20, 2032 (in the case of the 2032 Notes), we will have the right at our option, at any time and from time to time, to redeem all or any portion of the notes on not less than 30 nor more than 60 days’ prior notice mailed to the holders of the notes to be redeemed at a redemption price equal to 100% of the principal amount of the notes to be redeemed.

The redemption price for the notes will include, in each case, accrued and unpaid interest on the principal amount of the notes to be redeemed through the redemption date.

“Comparable Treasury Issue” means the United States Treasury security selected by an Independent Investment Banker that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of the notes of the relevant series.

“Independent Investment Banker” means one of the Reference Treasury Dealers appointed by us.

“Comparable Treasury Price” means, with respect to any redemption date, (1) the average of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) on the third business day preceding the redemption date or, in the case of satisfaction and discharge and defeasance, as of the third business day preceding the deposit of funds to pay the notes with the trustee, as set forth in the daily statistical release (or any successor release) published by the Federal Reserve Bank of New York and designated “Composite 3:30 p.m. Quotations for U.S. Government Notes” or (2) if such release (or any successor release) is not published or does not contain such prices on such business day, (a) the average of the Reference Treasury Dealer Quotations for such redemption date, after excluding the highest and lowest of such Reference Treasury Dealer Quotations, or (b) if we obtain fewer than four such Reference Treasury Dealer Quotations, the average of all Quotations obtained.

“Reference Treasury Dealer” means Credit Suisse Securities (USA) LLC, BofA Securities, Inc. and Citigroup Global Markets Inc., or their respective successors, and two other nationally recognized investment banking firms that are Primary Treasury Dealers specified from time to time by us, except that if any of the foregoing ceases to be a primary U.S. Government securities dealer in New York City (a “Primary Treasury Dealer”), we are required to designate as a substitute another nationally recognized investment banking firm that is a Primary Treasury Dealer.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any redemption date, the average, as determined by us, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to us by such Reference

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Treasury Dealer as of 3:30 p.m., New York City time, on the third business day preceding such redemption date or, in the case of satisfaction and discharge and defeasance, as of the third business day preceding the deposit of funds to pay the notes with the trustee.

“Treasury Rate” means, with respect to any redemption date, the rate per annum equal to the semiannual equivalent yield to maturity (computed as of the second business day immediately preceding the redemption date or, in the case of satisfaction and discharge and defeasance, as of the second business day prior to the deposit of funds to pay the notes with the trustee) of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for the redemption date.

On and after any redemption date, interest will cease to accrue on the notes called for redemption. Prior to any redemption date, we are required to deposit with a paying agent money sufficient to pay the redemption price of and accrued interest on the notes to be redeemed on such date. If we are redeeming less than all the notes of a series, the trustee under the indenture must select the notes to be redeemed by a method the trustee deems fair and appropriate in accordance with methods generally used at the time of selection by fiduciaries in similar circumstances.

We may, in any notice of redemption delivered to the holders of the notes, specify in our discretion one or more conditions precedent that must be satisfied prior to our obligation to so redeem the notes subject to notice of redemption.

Book-entry system

Upon issuance, each series of notes will be represented by one or more fully registered global certificates, each of which we refer to as a global security. Each global security will be deposited with, or on behalf of, the Depository Trust Company or DTC, and registered in the name of DTC or a nominee thereof. Unless and until it is exchanged in whole or in part for notes in definitive form, no global security may be transferred except as a whole by DTC to a nominee of DTC or by a nominee of DTC to DTC or another nominee of DTC or by DTC or any such nominee to a successor of DTC or a nominee of such successor. Account holders in the Euroclear Bank

SA/NV and Clearstream Banking S.A. clearance systems may hold beneficial interests in the notes through the accounts that each of these systems maintains as a participant in DTC.

A description of DTC’s procedures with respect to the global securities is set forth in the section “Book-Entry Securities” in the accompanying prospectus.

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CERTAIN UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS

The following discussion summarizes certain United States federal income tax considerations that may be relevant to you if you invest in the notes. This discussion is based on the Internal Revenue Code of 1986, as amended (the “Code”), Treasury Regulations promulgated thereunder, judicial decisions, and published rulings and administrative pronouncements of the United States Internal Revenue Service (“IRS”), each in effect as of the date of this offering. These authorities may change or be subject to differing interpretations. Any such change may be applied retroactively in a manner that results in United States federal income tax consequences different from those discussed below. We have not sought and will not seek any rulings from the IRS regarding the matters discussed below. There can be no assurance that the IRS or a court will not take a contrary position regarding the tax consequences of the purchase, ownership and disposition of our notes.

This discussion applies only to holders that hold notes as “capital assets” within the meaning of Section 1221 of the Code (generally, property held for investment). In addition, this discussion is limited to persons purchasing the notes pursuant to this prospectus supplement for cash at original issue and at the original “issue price” of the applicable series of notes within the meaning of Section 1273 of the Code (i.e., the first price at which a substantial amount of the applicable series of notes is sold to the public for cash). This summary does not address all United States federal income tax considerations that may be relevant to you if you are an investor that may be subject to special tax rules, such as a financial institution, bank, thrift, real estate investment trust, regulated investment company, insurance company, dealer in securities or currencies, trader in securities or commodities that elects mark to market treatment, person that will hold notes as a part of a “straddle,” conversion, hedging, or other integrated transaction or as a part of a ‘‘synthetic security’’ or other similar financial transaction, person that purchases or sells notes as part of a wash sale for tax purposes,tax-exempt organization, partnership or other entity classified as a partnership for United States federal income tax purposes (or investor in such entities), U.S. holder (as defined below) whose “functional currency” is not the United States dollar, controlled foreign corporation, passive foreign investment company, corporation that accumulates earnings to avoid United States federal income tax, former United States citizen or resident, person subject to special tax accounting rules as a result of any item of gross income with respect to the notes being taken into account in an applicable financial statement or person that holds one of our existing 2.15% Senior Notes due 2021 or our existing 2.25% Senior Notes due 2022 (which we expect to repay with a portion of the proceeds from this offering). In addition, this summary does not discuss any foreign, state or local tax considerations, any United States federal alternative minimum tax considerations or any United States federal tax considerations other than income tax considerations, such as estate or gift tax considerations.

If a partnership (or other entity taxed as a partnership for United States federal income tax purposes) holds notes, the tax treatment of a partner in the partnership generally will depend on the status of the partner, upon the activities of the partnership, and upon certain determinations made at the partner level. Accordingly, if you are a partnership holding our notes or a partner in such partnership, you should consult your tax advisor regarding the specific United States federal income tax consequences to you.

This discussion is included for general information only and does not address every aspect of the income or other tax laws that may be relevant to you in light of your particular circumstances. You should consult your tax adviser about the tax consequences of purchasing, holding or disposing notes, including the relevance to your particular situation of the considerations discussed below, as well as the relevance to your particular situation of state, local or other tax laws.

United States Federal Income Tax Consequences Applicable to U.S. Holders

This discussion applies only to holders of notes that are U.S. holders. For the purposes of this discussion, you will be a U.S. holder if, for United States federal income tax purposes, you are a beneficial owner of the notes and you are (i) an individual who is a citizen or resident of the United States, (ii) a corporation (or other entity taxable as a corporation for United States federal income tax purposes) created or organized under the laws

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of the United States, any state thereof, or the District of Columbia, (iii) an estate, the income of which is subject to United States federal income tax regardless of its source or (iv) a trust that is subject to the primary supervision of a United States court and the control of one or more “United States persons” (within the meaning of Section 7701(a)(30) of the Code) or that has otherwise validly elected to be treated as a United States person.

Payments or Accruals of Interest.    It is anticipated that the notes will not be deemed to be issued with original issue discount for United States federal income tax purposes and the remainder of this discussion so assumes. Accordingly, payments or accruals of stated interest on a note generally will be taxable to you as ordinary income at the time that you receive or accrue the interest (in accordance with your regular method of tax accounting).

Additional Payments.    In certain circumstances (see “Description of the Notes—We are obligated to purchase debt securities upon a change in control”), we may be obligated to make payments in excess of stated interest and the principal amount of the notes. We intend to take the position that the notes should not be treated as contingent payment debt instruments despite the possibility that these additional payments may be made. This position is based in part on assumptions that the likelihood, as of the date of issuance of the notes, that the additional payments will be paid is remote. Our position is binding on you unless you disclose your contrary position in the manner required by applicable Treasury Regulations. The IRS, however, may take a contrary position, which could affect the timing and character of your income with respect to the notes. You should consult your tax advisor about the potential application of the contingent payment debt instrument rules to the notes and the consequences thereof. The remainder of this discussion assumes that the notes are not treated as contingent payment debt instruments.

Sale, Exchange, Retirement, Redemption or Other Taxable Disposition of the Notes.    You generally will recognize gain or loss on the sale, exchange, retirement, redemption or other taxable disposition of our notes. The amount of gain or loss generally will be equal to the difference between the amount you realize on the transaction (less any accrued but unpaid interest, which will be subject to tax in the manner described above under “Payments or Accruals of Interest”) and your adjusted tax basis in the note. Your adjusted tax basis in a note generally will equal the cost of the note to you.

The gain or loss that you recognize on the sale, exchange, retirement, redemption or other taxable disposition of a note generally will be capital gain or loss, which will be long-term capital gain or loss if you have held the note for more than one year on the date of disposition. Net long-term capital gain recognized by an individual U.S. holder generally will be subject to tax at a lower rate than net short-term capital gain or ordinary income. The deductibility of capital losses is subject to limitations.

Medicare Tax on Net Investment Income.    Certain U.S. holders who are individuals, estates or trusts may be subject to a 3.8% tax on certain investment income, including interest, and gain from the disposition of our notes, less certain deductions. U.S. holders should consult their tax advisors regarding the effect, if any, of this tax on their ownership of our notes.

United States Federal Income Tax Consequences Applicable toNon-U.S. Holders

This discussion applies only to holders of notes that arenon-U.S. holders. For purposes of this discussion, a“non-U.S. holder” is a beneficial owner of the notes that is not a U.S. holder (as defined above) or an entity treated as a partnership for United States federal income tax purposes.

Payments or Accruals of Interest.    Subject to the discussions below on backup withholding and FATCA, if you are anon-U.S. holder, interest income that you derive in respect of the notes generally will not be subject to United States federal income or withholding tax, provided that:

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If you are anon-U.S. holder, even if you do not satisfy the requirements in the preceding paragraph, you may be entitled to a reduction in or an exemption from United States federal withholding tax on interest if either (a) you are entitled to benefits under an applicable income tax treaty or (b) you hold our notes in connection with the conduct of a trade or business within the United State and the interest being paid is effectively connected with that trade or business. To claim such a reduction or exemption from withholding, you must, prior to the payment date, provide the applicable withholding agent with a properly executed (a) IRS FormW-8BEN or FormW-8BEN-E (or other applicable form) claiming reduction or exemption under the benefits of an applicable income tax treaty, or (b) IRS FormW-8ECI (or other applicable form) stating that interest paid on a note is not subject to withholding tax because it is effectively connected with the conduct of a trade or business within the United States.

If the interest paid to you is effectively connected with your conduct of a trade or business in the United States (and, if required by an applicable income tax treaty, you maintain a United States permanent establishment or fixed base to which such interest is attributable), then, although exempt from United States federal withholding tax (provided you furnish the appropriate certification, as described above), you generally will be subject to United States federal income tax on the interest in the same manner as if you were a U.S. holder. In addition, if you are a foreign corporation, you may be subject to a branch profits tax equal to 30% (or a lower applicable income tax treaty rate) on a portion of your effectively connected earnings and profits for the taxable year. If you are anon-U.S. holder, you should consult your tax advisor regarding your entitlement to benefits under any applicable income tax treaty.

Sale, Exchange, Retirement, Redemption or Other Taxable Disposition of the Notes.    Subject to the discussions below on backup withholding and FATCA, and except with respect to accrued but unpaid interest (which may be subject to tax as described above), if you are anon-U.S. holder, you generally will not be subject to United States federal income tax on any gain realized upon the sale, exchange, retirement, redemption or other disposition of our notes unless:

You generally will be subject to United States federal income tax on the gain described in the first bullet point in the preceding paragraph in the same manner as if you were a U.S. holder. If you are a foreign corporation, you also may be subject to a branch profits tax at a rate of 30% (or lower applicable income tax treaty rate) on a portion of your effectively connected earnings and profits for the taxable year. If you are anon-U.S. holder described in the second bullet point in the preceding paragraph, you generally will be subject to United States federal income tax at a rate of 30% (or lower applicable income tax treaty rate) on any gain derived from the sale or other disposition, which may be offset by certain United States source capital losses (even though you are not considered a resident of the United States) provided you timely file United States federal income tax returns with respect to those losses.

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Information Reporting and Backup Withholding

Payments of interest made by us on, or the proceeds of the sale or other disposition of, the notes to U.S. holders andnon-U.S. holders may be subject to U.S. information reporting and may also be subject to U.S. federal backup withholding if the recipient of the payment fails to supply an accurate taxpayer identification number or otherwise fails to comply with applicable U.S. information reporting and certification requirements. Any amount withheld under the backup withholding rules may be allowable as a refund or credit against the holder’s U.S. federal income tax liability, provided that the required information is timely furnished to the IRS.

FATCA

Under Sections 1471 to 1474 of the Code, Treasury Regulations promulgated thereunder and applicable administrative guidance (collectively, ‘‘FATCA’’), United States withholding tax may also apply to certain types of payments made to ‘‘foreign financial institutions,’’ as defined under such rules, and certain othernon-U.S. entities. FATCA generally imposes a 30% withholding tax on payments of interest on, and (subject to the proposed Treasury Regulations discussed below) the gross proceeds from the sale, retirement or other disposition of, notes paid to a foreign financial institution unless the foreign financial institution enters into an agreement with the Treasury and complies with the reporting and withholding requirements thereunder or, in the case of a foreign financial institution in a jurisdiction that has entered into an intergovernmental agreement with the United States, complies with the requirements of such agreement. In addition, FATCA generally imposes a 30% withholding tax on the same types of payments to anon-financial foreign entity unless the entity certifies that it does not have any substantial United States owners or furnishes identifying information regarding each substantial United States owner. Proposed Treasury Regulations eliminate withholding under FATCA on payments of gross proceeds. Taxpayers may rely on these proposed Treasury Regulations until final Treasury Regulations are issued, but such Treasury Regulations are subject to change. An applicable intergovernmental agreement regarding FATCA between the United States and a foreign jurisdiction may modify the rules discussed in this paragraph. Prospective investors should consult their tax advisors regarding FATCA.

PROSPECTIVE INVESTORS ARE ADVISED TO CONSULT THEIR TAX ADVISORS CONCERNING THE APPLICATION OF THE UNITED STATES FEDERAL TAX LAWS TO THEIR PARTICULAR CIRCUMSTANCES AS WELL AS ANY TAX CONSEQUENCES ARISING UNDER THE LAWS OF ANY STATE, LOCAL OR FOREIGN TAXING JURISDICTION PRIOR TO MAKING SUCH INVESTMENT.

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UNDERWRITING

Credit Suisse Securities (USA) LLC, BofA Securities, Inc. and Citigroup Global Markets Inc. are acting as representatives of the underwriters named below. Subject to the terms and conditions set forth in an underwriting agreement dated the date of this prospectus supplement, we have agreed to sell to the underwriters, and each underwriter named below has agreed, severally and not jointly, to purchase from us, the principal amount of notes set forth opposite its name below.

Subject to the terms and conditions set forth in the underwriting agreement, the underwriters have agreed, severally and not jointly, to purchase all of the notes sold under the underwriting agreement if any of these notes are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the nondefaulting underwriters may be increased or the underwriting agreement may be terminated.

We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the underwriters may be required to make in respect of those liabilities.

The underwriters are offering the notes, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel and other conditions. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commissions and Discounts

The underwriters initially propose to offer the notes to the public at the public offering price that appears on the cover page of this prospectus supplement. The underwriters may offer the notes to selected dealers at the public offering price minus a concession of up to 0.250% of the principal amount of the 2027 Notes, up to 0.300% of the principal amount of the 2030 Notes and up to 0.325% of the principal amount of the 2032 Notes. After the initial offering, the underwriters may change the public offering prices and any other selling terms. The underwriters may offer and sell notes through certain of their affiliates.

The following table shows the underwriting discounts and commissions we will pay to the underwriters in connection with the offering (expressed as a percentage of the principal amount of the notes).

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We estimate that our expenses in connection with the sale of the notes (excluding the underwriting discounts and commissions), will be approximately $6.4 million and will be payable by us. The underwriters have agreed to reimburse us up to $2.0 million of our out-of-pocket expenses in connection with this offering.

New Issue of Notes

Each series of notes is a new issue of securities with no established trading market. We do not intend to apply for listing of the notes on any securities exchange or for inclusion of the notes on any automated dealer quotation system. We have been advised by the underwriters that they presently intend to make a market in the notes of each series after completion of the offering. However, they are under no obligation to do so and may discontinue any market-making activities at any time without any notice. We cannot assure the liquidity of the trading markets for the notes or that active public markets for the notes will develop. If active public trading markets for the notes do not develop, the market prices and liquidity of the notes may be adversely affected. If the notes are traded, they may trade at a discount from their initial offering prices, depending on prevailing interest rates, the market for similar securities, our operating performance and financial condition, general economic conditions and other factors.

Price Stabilization, Short Positions

In connection with the offering of the notes, the underwriters may engage in overallotment, stabilizing transactions and syndicate covering transactions. Overallotment involves sales in excess of the offering size, which creates a short position for the underwriters. Stabilizing transactions involve bids to purchase the notes in the open market for the purpose of pegging, fixing or maintaining the prices of the notes. Syndicate covering transactions involve purchases of the notes in the open market after the distribution has been completed in order to cover short positions. Stabilizing transactions and syndicate covering transactions may cause the prices of the notes to be higher than it would otherwise be in the absence of those transactions. If the underwriters engage in stabilizing or syndicate covering transactions, they may discontinue them at any time.

We do not, nor do any of the underwriters, make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the prices of the notes. In addition, neither we nor any of the underwriters makes any representation that the underwriters will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

Other Relationships

Some of the underwriters and their respective affiliates have provided, or may in the future provide, investment banking, commercial banking and other financial and advisory services in the ordinary course of business to us or our affiliates, including lending and other related services, underwriting and the provision of financial advice, and have received, or may in the future receive, customary fees and commissions for their services. Certain affiliates of the underwriters are lenders to Costco or provide other banking services. U.S. Bancorp Investments, Inc., one of the underwriters, is an affiliate of the trustee. In addition, in the ordinary course of their business activities, the underwriters and their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. For example, certain of the underwriters or their affiliates own portions of our existing 2.15% Senior Notes due 2021 and 2.25% Senior Notes due 2022, and they may receive a portion of the net proceeds that we use from this offering to repay their 2.15% Senior Notes due 2021 or 2.25% Senior Notes due 2022. If any of the underwriters or their affiliates have a lending relationship with us, certain of those underwriters or their affiliates routinely hedge, certain of those underwriters are likely to hedge or otherwise reduce their credit exposure to us and certain other of those underwriters may hedge, their credit exposure to us consistent with their customary risk management policies. Typically, these underwriters and their affiliates would hedge such exposure by entering

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into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities, including potentially the notes offered hereby. Any such credit default swaps or short positions could adversely affect future trading prices of the notes offered hereby. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Electronic Distribution

In connection with the offering, certain of the underwriters or securities dealers may distribute this prospectus by electronic means, such ase-mail.

Selling Restrictions

European Economic Area and United Kingdom

The notes are not intended to be offered, sold or otherwise made available to and should not be offered, sold or otherwise made available to any retail investor in the European Economic Area (the “EEA”) or in the United Kingdom (the “UK”). For these purposes, a retail investor means a person who is one (or more) of: (i) a retail client as defined in point (11) of Article 4(1) of Directive 2014/65/EU (as amended, “MiFID II”); (ii) a customer within the meaning of Directive (EU) 2016/97 (the “Insurance Distribution Directive”), where that customer would not qualify as a professional client as defined in point (10) of Article 4(1) of MiFID II; or (iii) not a qualified investor as defined in Regulation (EU) 2017/1129 (the “Prospectus Regulation”). Consequently no key information document required by Regulation (EU) No 1286/2014 (as amended, the “PRIIPs Regulation”) for offering or selling the notes or otherwise making them available to retail investors in the EEA or in the UK has been prepared and therefore offering or selling the notes or otherwise making them available to any retail investor in the EEA or in the UK may be unlawful under the PRIIPs Regulation. This prospectus supplement has been prepared on the basis that any offer of notes in any Member State of the EEA or in the UK will be made pursuant to an exemption under the Prospectus Regulation from the requirement to publish a prospectus for offers of notes. This prospectus supplement is not a prospectus for the purposes of the Prospectus Regulation.

United Kingdom

This prospectus supplement and the accompanying prospectus are only being distributed to and are only directed at (i) persons who are outside the United Kingdom or (ii) to investment professionals falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 (“the Order”), or (iii) high net worth companies, and other persons to whom it may lawfully be communicated, falling within Article 49(2)(a) to (d) of the Order, all such persons together being referred to as “relevant persons.” The notes are only available to, and any invitation, offer or agreement to subscribe, purchase or otherwise acquire the notes will be engaged in only with, relevant persons. Any person who is not a relevant person should not act or rely on this prospectus supplement, the accompanying prospectus or any of the respective contents.

Each Underwriter has:

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Canada

The notes may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the notes must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (“NI 33-105”), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

United Kingdom

In the United Kingdom, this document is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at persons who are “qualified investors” (as defined in the Prospectus Regulation) (i) who have professional experience in matters relating to investments falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (the “Order”) and/or (ii) who are high net worth companies (or persons to whom it may otherwise be lawfully communicated) falling within Article 49(2)(a) to (d) of the Order (all such persons together being referred to as “relevant persons”) or otherwise in circumstances which have not resulted and will not result in an offer to the public of the shares in the United Kingdom.

Any person in the United Kingdom that is not a relevant person should not act or rely on the information included in this document or use it as basis for taking any action. In the United Kingdom, any investment or investment activity that this document relates to may be made or taken exclusively by relevant person.

Switzerland

This prospectus supplement is not intended to constitute an offer or solicitation to purchase or invest in the notes. The notes may not be publicly offered, directly or indirectly, in Switzerland within the meaning of the Swiss Financial Services Act (“FinSA”) and no application has or will be made to admit the notes to trading on any trading venue (exchange or multilateral trading facility) in Switzerland. Neither this prospectus supplement nor any other offering or marketing material relating to the notes constitutes a prospectus pursuant to the FinSA, and neither this prospectus supplement nor any other offering or marketing material relating to the notes may be publicly distributed or otherwise made publicly available in Switzerland.

T+2 Settlement

We expect that delivery of the notes will be made against payment thereof on or about the closing date specified on the cover page of this prospectus supplement, which will be the second business day following the date of pricing of the notes (this settlement cycle being referred to as “T+2”).

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LEGAL MATTERS

The validity of the notes will be passed upon for us by Perkins Coie LLP, Seattle, Washington, and for the underwriters by Latham & Watkins LLP, Los Angeles, California. Latham  & Watkins LLP represents Costco from time to time in unrelated matters.

EXPERTS

The consolidated financial statements of Costco Wholesale Corporation as of September 1, 2019 and September 2, 2018, and for the52-week period ended September 1, 2019, the 52-week period ended September 2, 2018, and the 53-week period ended September 3, 2017, and management’s assessment of the effectiveness of internal control over financial reporting as of September 1, 2019 have been incorporated by reference herein in reliance upon the reports of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

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PROSPECTUS

Debt Securities

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission using a “shelf” registration process. This means:

We will provide the specific terms of these securities in supplements to this prospectus. You should carefully read this prospectus and the applicable prospectus supplement before you invest.

The securities may be sold directly to investors, through agents designated from time to time, or to or through underwriters or dealers. See “Plan of Distribution.” If any underwriters are involved in the sale of any securities in respect of which this prospectus is being delivered, the names of the underwriters and any applicable commissions or discounts will be set forth in the applicable prospectus supplement. The net proceeds we expect to receive from the sale also will be set forth in the applicable prospectus supplement.

Investing in our debt securities involves risks. You should consider therisk factors described in any accompanying prospectus supplement or any documents we incorporate by reference.

This prospectus may not be used to offer or sell any securities unless accompanied by a prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is April 15, 2020.

TABLE OF CONTENTS

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ABOUT THIS PROSPECTUS

This prospectus is part of a “shelf” registration statement on FormS-3 that we have filed with the Securities and Exchange Commission (the “SEC”). By using a shelf registration statement, we may sell the debt securities at any time and from time to time in one or more offerings. The exhibits to our registration statement contain the full text of certain contracts and other important documents we have summarized in this prospectus. Since these summaries may not contain all the information that you may find important in deciding whether to purchase the debt securities we offer, you should review the full text of these documents. The registration statement and the exhibits can be obtained from the SEC as indicated under the heading “Where You Can Find Additional Information.”

This prospectus only provides you with a general description of the debt securities we may offer. Each time we sell debt securities, we will provide a prospectus supplement that contains specific information about the terms of those debt securities. The prospectus supplement may also add, update or change information contained in this prospectus and, accordingly, to the extent inconsistent, information in this prospectus is superseded by the information in the applicable prospectus supplement. You should read both this prospectus and any prospectus supplement together with the additional information described below under the heading “Where You Can Find Additional Information.”

We are not making an offer of these debt securities in any jurisdiction where the offer is not permitted. You should not assume that the information in this prospectus or a prospectus supplement is accurate as of any date other than the date on the front of the document.

References in this prospectus to Costco, the Company, we, us and our are to Costco Wholesale Corporation (together with its subsidiaries) unless the context otherwise provides.

WHERE YOU CAN FIND ADDITIONAL INFORMATION

We file annual, quarterly and current reports and other information with the SEC. These reports and other information filed by us are also available free of charge through our website,http://www.costco.com. These reports and other information are also filed by us electronically with the SEC and are available at the SEC’s website,www.sec.gov.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” the information we file with it, which means that we can disclose important information to you by referring you to another document that we filed with the SEC. The information incorporated by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the document listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), until we sell all of the securities:

You may obtain a copy of these filings at no cost by writing or telephoning us at 999 Lake Drive, Issaquah, Washington 98027, telephone (425)313-8100, attention Investor Relations Department, or through our website, www.costco.com. Information contained on our website does not constitute part of this prospectus.

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You should rely only on the information contained or incorporated by reference in this prospectus, any supplemental prospectus or any pricing supplement. We have not authorized anyone to provide you with any other information. We are not making an offer of these securities in any jurisdiction where the offer is not permitted. You should not assume that the information in this prospectus, any accompanying prospectus supplement, or any document incorporated by reference is accurate as of any date other than the date on the front of the document.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference contain certain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Exchange Act. They include statements that address activities, events, conditions or developments that we expect or anticipate may occur in the future and may relate to such matters as sales growth, changes in comparable sales, cannibalization of existing locations by new openings, price or fee changes, earnings performance, earnings per share, stock-based compensation expense, warehouse openings and closures, capital spending, the effect of adopting certain accounting standards, future financial reporting, financing, margins, return on invested capital, strategic direction, expense controls, membership renewal rates, shopping frequency, litigation, and the demand for our products and services. Forward-looking statements may also be identified because they contain words such as “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “likely,” “may,” “might,” “plan,” “potential,” “predict,” “project,” “seek,” “should,” “target,” “will,” “would,” or similar expressions and the negatives of those terms.

Forward-looking statements provide our expectations or predictions of future conditions, events or results. They are not guarantees of future performance. By their nature, forward-looking statements involve risks and uncertainties. These statements speak only as of the date they are made. We do not undertake to update forward-looking statements to reflect the impact of circumstances or events that arise after the date the forward-looking statements were made, except as may be required by law. There are a number of factors, many of which are beyond our control, that may cause actual events, results, or performance to differ materially from those described in the forward-looking statements. These factors include, but are not limited to, domestic and international economic conditions, including exchange rates, the effects of competition and regulation, uncertainties in the financial markets, consumer and small business spending patterns and debt levels, breaches of security or privacy of member or business information, conditions affecting the acquisition, development, ownership or use of real estate, capital spending, actions of vendors, rising costs associated with employees (generally including health care costs), energy, and certain commodities, geopolitical conditions (including tariffs), the ability to maintain effective internal control over financial reports, the effects of theCOVID-19 coronavirus outbreak, including among others, the duration of the pandemic, the unknown long-term economic impact, reduced customer shopping due to illness, travel restrictions or financial hardship, shifts in demand away from discretionary or higher priced products to lower priced products, reduced workforce due to illness, quarantine, or government mandates, supply chain disruptions, or temporary store closures due to reduced workforces or government mandates, and other factors described in Part I, Item 1A of our most recent Annual Report onForm 10-K and our Quarterly Reports on Form10-Q in the section entitled “Risk Factors” and as may be included from time to time in our reports filed with the SEC.

THE COMPANY

Costco operates membership warehouses based on the concept that offering members low prices on a limited selection of nationally branded and select private-label products in a wide range of merchandise categories will produce high sales volumes and rapid inventory turnover. When combined with the operating efficiencies achieved by volume purchasing, efficient distribution and reduced handling of merchandise inno-frills, self-service warehouse facilities, these volumes and turnover enable Costco to operate profitably at significantly lower gross margins (net sales less merchandise costs) than most other retailers.

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At April 8, 2020, Costco operated 787 warehouses worldwide: 547 in the United States (U.S.) located in 45 U.S. states, Washington, D.C., and Puerto Rico, 100 in Canada, 39 in Mexico, 29 in the United Kingdom (U.K.), 26 in Japan, 16 in Korea, 13 in Taiwan, 12 in Australia, two in Spain and one each in Iceland, France and China. The Company operatese-commerce websites in the U.S., Canada, Mexico, U.K., Korea, Taiwan, Japan and Australia.

Our principal executive office is located at 999 Lake Drive, Issaquah, Washington 98027 and our telephone number is(425) 313-8100.

RISK FACTORS

Investing in the debt securities involves risks. Before making a decision to invest in the debt securities, you should carefully consider the risks described in the sections entitled “Risk Factors” in any prospectus supplement and those set forth in the documents incorporated by reference in this prospectus and any applicable prospectus supplement, as well as other information in this prospectus and any applicable prospectus supplement. Each of the risks described in these sections and documents could materially and adversely affect our business, financial condition, results of operations and prospects, and could result in a loss of your investment. Additional risks and uncertainties not known to us or that we deem immaterial may also impair our business, financial condition, results of operations and prospects.

USE OF PROCEEDS

Unless otherwise specified in the applicable prospectus supplement, we intend to use the net proceeds from the sale of the debt securities for general corporate purposes. Examples of general corporate purposes include additions to working capital, repayment of existing debt, repurchase of common stock, and expansion of warehouse, manufacturing and distribution facilities.

DESCRIPTION OF DEBT SECURITIES

The following description of the debt securities sets forth the material terms and provisions of the debt securities to which any prospectus supplement may relate. The particular terms of the debt securities offered by any prospectus supplement (the “Offered Debt Securities”) and the extent, if any, to which these general provisions may apply to the Offered Debt Securities, will be described in the prospectus supplement relating to the Offered Debt Securities. Accordingly, for a description of the terms of a particular issue of debt securities, reference must be made to both the prospectus supplement relating thereto and to the following description.

The debt securities will be our general obligations. The debt securities will be issued under a First Supplemental Indenture dated as of March 20, 2002, between Costco and U.S. Bank National Association, as trustee, which we refer to as the “supplemental indenture,” supplement to a Senior Debt Securities Indenture dated as of October 26, 2001, between Costco and the trustee, which we refer to together with the supplemental indenture as the “indenture.”

We have summarized selected provisions of the indenture below. The indenture has been incorporated by reference as an exhibit into the registration statement of which this prospectus is a part and you should read the indenture for provisions that may be important to you. Accordingly, the following summary is qualified in its entirety by reference to the provisions of the indenture. Unless otherwise specified, capitalized terms used in this summary have the meanings specified in the indenture.

General

The indenture does not limit the aggregate principal amount of debt securities which may be issued under the indenture and provides that debt securities may be issued from time to time in one or more series. The indenture does not limit the amount of other indebtedness or debt securities.

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Unless otherwise provided in a prospectus supplement, the debt securities will be our unsecured obligations. The debt securities will rank equally with all other unsecured and unsubordinated indebtedness of ours.

The debt securities may be issued in fully registered form without coupons (“registered securities”) or in the form of one or more global securities (each a “Global Security”). Registered securities that are book-entry securities will be issued as registered Global Securities. Unless otherwise provided in the prospectus supplement, the debt securities will be only registered securities. The debt securities will be issued, unless otherwise provided in the prospectus supplement, in denominations of $1,000 or an integral multiple thereof for registered securities.

The prospectus supplement relating to the particular debt securities offered thereby will describe the following terms of the Offered Debt Securities:

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No service charge will be made for any transfer or exchange of the debt securities except for any tax or other governmental charge.

Debt securities of a single series may be issued at various times with different maturity dates and different principal repayment provisions, may bear interest at different rates, may be issued at or above par or with an original issue discount, and may otherwise vary, all as provided in the indenture. The prospectus supplement for any debt securities issued above par or with an original issue discount will state any applicable material federal income tax consequences and other special considerations.

Exchange, Registration and Transfer

Registered securities (other than book-entry securities) of any series of Offered Debt Securities will be exchangeable for other registered securities of the same series and of a like aggregate principal amount and tenor of different authorized denominations.

Debt securities may be presented for exchange as provided above, and registered securities (other than book-entry securities) may be presented for registration of transfer (with the form of transfer endorsed thereon duly endorsed), at the office of the Security Registrar or at the office of any transfer agent designated by us for this purpose with respect to any series of debt securities and referred to in the prospectus supplement. No service charge will be charged for the transfer, but any tax or other governmental charge must be paid. Such transfer or exchange will be effected upon the Security Registrar or such transfer agent, as the case may be, being satisfied with the documents of title and identity of the person making the request. If a prospectus supplement refers to any transfer agents (in addition to the Security Registrar) initially designated by us with respect to any series of debt securities, we may at any time rescind the designation of any such transfer agent or approve a change in the location through which any such transfer agent acts, except that, if debt securities of a series are issuable solely as registered securities, we will be required to maintain a transfer agent in each Place of Payment for such series. We may at any time designate additional transfer agents with respect to any series of debt securities.

In the event of any redemption in part, we will not be required to:

For a discussion of restrictions on the exchange, registration and transfer of Global Securities, see “Global Securities.”

Payment and Paying Agents

Unless otherwise provided in the prospectus supplement, payment of principal of (and premium, if any) and interest, if any, on registered securities will be made in U.S. dollars at the office of such Paying Agent or Paying Agents as we may designate from time to time, except that at our option payment of any interest may be made by check mailed to the address of the Person entitled thereto as that address shall appear in the Security Register. Unless otherwise provided in a prospectus supplement, payment of any installment of interest on registered securities will be made to the Person in whose name the registered security is registered at the close of business on the Regular Record Date for the interest.

Unless otherwise provided in a prospectus supplement, the Corporate Trust Office of the trustee will be designated as our sole Paying Agent for payments with respect to Offered Debt Securities that are issuable solely

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as registered securities. Any Paying Agents outside the United States and any other Paying Agents in the United States initially designated by us for the Offered Debt Securities will be named in a prospectus supplement. We may at any time designate additional Paying Agents or rescind the designation of any Paying Agent or approve a change in the office through which any Paying Agent acts, except that, if debt securities of a series are issuable solely as registered securities, we will be required to maintain a Paying Agent in each Place of Payment for that series.

All moneys paid by us to a Paying Agent for the payment of principal of (and premium, if any) or interest, if any, on any debt security or coupon that remain unclaimed at the end of two years after such principal, premium or interest shall have become due and payable will be repaid to us and the holder of such debt security or coupon will thereafter look only to us for payment thereof.

Global Securities

The debt securities of a series may be issued in whole or in part as one or more Global Securities that will be deposited with, or on behalf of, a depositary located in the United States (a “U.S. Depositary”) or a common depositary located outside the United States (a “Common Depositary”) identified in the prospectus supplement relating to the series. Global Securities will be issued in registered form, in either temporary or definitive form.

The specific terms of the depositary arrangement with respect to any debt securities of a series will be described in the prospectus supplement relating to the series. We anticipate that the following provisions will apply to all depositary arrangements with a U.S. Depositary or Common Depositary.

Book-Entry Securities

Unless otherwise specified in a prospectus supplement, debt securities which are to be represented by a Global Security to be deposited with or on behalf of a U.S. Depositary will be represented by a Global Security registered in the name of the depositary or its nominee. Upon the issuance of a Global Security in registered form, the U.S. Depositary for the Global Security will credit, on its book-entry registration and transfer system, the respective principal amounts of the debt securities represented by the Global Security to the accounts of institutions that have accounts with the depositary or its nominee (“participants”). The accounts to be credited shall be designated by the underwriters or agents of the debt securities or by us, if the debt securities are offered and sold directly by us. Ownership of beneficial interests in the Global Securities will be limited to participants or persons that may hold interests through participants. Ownership of beneficial interests in the Global Securities will be shown on, and the transfer of that ownership will be effected only through, records maintained by the U.S. Depositary or its nominee for the Global Security or by participants or persons that hold through participants. The laws of some jurisdictions require that certain purchasers of securities take physical delivery of the securities in definitive form. These limits and laws may impair the ability to transfer beneficial interests in a Global Security.

So long as the U.S. Depositary for a Global Security in registered form, or its nominee, is the registered owner of the Global Security, the depositary or nominee, as the case may be, will be considered the sole owner or holder of the debt securities represented by the Global Security for all purposes under the indenture governing the debt securities. Except as set forth below, owners of beneficial interests in these Global Securities will not be entitled to have debt securities of the series represented by the Global Security registered in their names, will not receive or be entitled to receive physical delivery of debt securities of the series in definitive form and will not be considered the owners or holders thereof under the indenture.

Payment of principal of (and premium, if any) and interest, if any, on debt securities registered in the name of or held by a U.S. Depositary or its nominee will be made to the U.S. Depositary or its nominee, as the case may be, as the registered owner or the holder of the Global Security representing the debt securities. Neither we nor any trustee or Paying Agent nor the Security Registrar for the debt securities will have any responsibility or liability

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for any aspect of the records relating to or payments made on account of beneficial ownership interests in a Global Security for the debt securities or for maintaining, supervising or reviewing any records relating to the beneficial ownership interests.

We expect that the U.S. Depositary for debt securities of a series, upon receipt of any payment of principal of (and premium, if any) or interest on permanent Global Securities, will credit participants’ accounts on the date the payment is payable in accordance with their respective beneficial interests in the principal amount of the Global Securities as shown on the records of the Depositary. We also expect that payments by participants to owners of beneficial interests in the Global Security held through the participants will be governed by standing instructions and customary practices, as is now the case with securities held for the accounts of customers registered in “street name,” and will be the responsibility of the participants.

Unless and until it is exchanged in whole for debt securities in definitive form, a Global Security may not be transferred except as a whole by the U.S. Depositary for the Global Security to a nominee of the Depositary or by a nominee of the Depositary to the Depositary or another nominee of the Depositary or by the Depositary or any nominee to a successor of the Depositary or a nominee of the successor. If a U.S. Depositary for debt securities in registered form is at any time unwilling or unable to continue as depositary and a successor depositary is not appointed by us within 90 days, we will issue debt securities in definitive registered form in exchange for the Global Security or Global Securities representing the debt securities. In addition, we may at any time and in our sole discretion determine not to have any debt securities in registered form represented by one or more Global Securities and, in such event, will issue debt securities in definitive registered form in exchange for the Global Security or Global Securities representing the debt securities. In this instance, an owner of a beneficial interest in a Global Security will be entitled to physical delivery in definitive form of debt securities of the series represented by the Global Security equal in principal amount to the beneficial interest and to have the debt securities registered in the name of the owner of the beneficial interest.

Absence of Restrictive Covenants

We are not restricted by the indenture from paying dividends or from incurring, assuming or becoming liable for any type of debt or other obligations or from creating liens on our property for any purpose. The indenture does not require the maintenance of any financial ratios or specified levels of net worth or liquidity. The indenture does not contain provisions which afford holders of the debt securities protection in the event of a highly leveraged transaction involving us.

Merger and Consolidation

The indenture provides that we, without the consent of the holders of any of the outstanding debt securities, may consolidate with or merge into any other corporation or transfer or lease our properties and assets substantially as an entirety to any Person or may permit any corporation to merge into us, provided that:

The indenture provides that, upon any consolidation or merger or transfer or lease of our properties and assets substantially as an entirety in accordance with the preceding paragraph, the successor corporation formed by the consolidation or into which we are merged or to which the transfer or lease is made shall be substituted for us with the same effect as if the successor corporation had been named as us. Thereafter, we shall be relieved of the

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performance and observance of all obligations and covenants of the indenture and the debt securities, including but not limited to the obligation to make payment of the principal of (and premium, if any) and interest, if any, on all the debt securities then outstanding, and we may thereupon or any time thereafter be liquidated and dissolved.

Satisfaction and Discharge

Unless a prospectus supplement provides otherwise, we will be discharged from our obligations under the outstanding debt securities of a series upon satisfaction of the following conditions:

Upon discharge in the manner described above, we will be deemed to have satisfied all the obligations under the indenture, except for obligations with respect to registration of transfer and exchange of the debt securities of such series, and the rights of the holders to receive from deposited funds payment of the principal of (and premium, if any) and interest, if any, on the debt securities of the series.

Modification of the Indenture

The indenture provides that we and the trustee thereunder may, without the consent of any holders of debt securities, enter into supplemental indentures for the purposes, among other things, of adding to our covenants, adding any additional Events of Default, establishing the form or terms of debt securities or curing ambiguities or inconsistencies in the indenture or making other provisions; provided this action shall not adversely affect the interests of the holders of any series of debt securities in any material respect.

The indenture contains provisions permitting us, with the consent of the holders of not less than a majority in principal amount of the outstanding debt securities of all affected series (acting as one class), to execute supplemental indentures adding any provisions to or changing or eliminating any of the provisions of the indenture or modifying the rights of the holders of the debt securities of such series, except that no supplemental indenture may, without the consent of the holders of all the outstanding debt securities affected thereby, among other things:

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Events of Default

An Event of Default in respect of any series of debt securities (unless it is either inapplicable to a particular series or has been modified or deleted with respect to any particular series) is defined in each indenture to be:

“Consolidated Subsidiary” is defined in the indenture as every Subsidiary which does not transact any substantial portion of its business or regularly maintain any substantial portion of its operating assets outside the United States or Canada other than (a) a Subsidiary acquired or organized after the date of the indenture which, prior to the date of acquisition or organization, shall have been classified by resolution of the Board of Directors or Executive Committee of the Board of Directors of Costco Wholesale Corporation as an Unconsolidated Subsidiary unless and until the Board of Directors or Executive Committee of the Board of Directors of Costco Wholesale Corporation shall by resolution reclassify such Subsidiary as a Consolidated Subsidiary; and (b) any Subsidiary of an Unconsolidated Subsidiary; provided, however, that an Unconsolidated Subsidiary shall not be a successor, directly or indirectly, to any Consolidated Subsidiary.

If an Event of Default shall have happened and be continuing, either the trustee thereunder or the holders of not less than 25% in principal amount of the outstanding debt securities of the series may declare the principal of all of the outstanding notes to be immediately due and payable.

The indenture provides that the holders of not less than a majority in principal amount of the outstanding debt securities of any series may direct the time, method and place of conducting any proceeding for any remedy

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available to the trustee thereunder, or exercising any trust or power conferred on the trustee, with respect to the debt securities of the series; provided that:

The indenture provides that the holders of not less than a majority in principal amount of the outstanding debt securities of any series may on behalf of the holders of all of the outstanding debt securities of such series waive any past default under such indenture with respect to such series and its consequences, except a default (1) in the payment of the principal of (or premium, if any) or interest, if any, on any of the debt securities of such series or (2) in respect of a covenant or provision of such indenture which, under the terms of such indenture, cannot be modified or amended without the consent of the holders of all of the outstanding debt securities of such series affected thereby.

The indenture contains provisions entitling the trustee thereunder, subject to the duty of the trustee during an Event of Default in respect of any series of debt securities to act with the required standard of care, to be indemnified by the holders of the debt securities of such series before proceeding to exercise any right or power under the indenture at the request of the holders of the debt securities of such series.

The indenture provides that the trustee will, within 90 days after the occurrence of a default in respect of any series of debt securities, give to the holders of the debt securities of such series notice of all uncured and unwaived defaults known to it; provided, however, that, except in the case of a default in the payment of the principal of (or premium, if any) or any interest on, or any sinking fund installment with respect to, any of the debt securities of such series, the trustee will be protected in withholding the notice if it in good faith determines that the withholding of the notice is in the interests of the holders of the debt securities of such series; and provided, further, that the notice shall not be given until at least 30 days after the occurrence of an Event of Default regarding the performance of any covenant of ours under the indenture other than for the payment of the principal of (or premium, if any) or any interest on, or any sinking fund installment with respect to, any of the debt securities of such series. The term default for the purpose of this provision only means any event that is, or after notice or lapse of time, or both, would become, an Event of Default with respect to the debt securities of such series.

We will be required to furnish annually to the trustee a certificate as to compliance with all conditions and covenants under the indenture.

Notices

Notices to holders of registered securities will be given by mail to the addresses of the holders as they appear in the Security Register.

Title

We, the appropriate trustee and any agent of ours or the trustee may treat the registered owner of any registered security (including registered securities in global registered form) as the absolute owner thereof (whether or not the debt security or coupon shall be overdue and notwithstanding any notice to the contrary) for the purpose of making payment and for all other purposes.

Governing Law

New York law will govern the indenture and the debt securities.

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PLAN OF DISTRIBUTION

We may sell the securities being offered hereby:

The distribution of the securities may be effected from time to time in one or more transactions either

Offers to purchase the securities may be solicited directly by us or by agents designated by us from time to time. Any agent, which may be deemed to be an underwriter as that term is defined in the Securities Act, involved in the offer or sale of the debt securities in respect of which this prospectus is delivered will be named, and any commissions payable by us to the agent will be set forth in the prospectus supplement relating to the offering of the securities. Unless otherwise indicated in the applicable prospectus supplement, any agent will be acting on a best efforts basis for the period of its appointment.

If a dealer is utilized in the sale of the securities in respect of which this prospectus is delivered, we will sell the securities to the dealer, as principal. The dealer, which may be deemed to be an underwriter as that term is defined in the Securities Act, may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale. Dealer trading may take place in certain of the securities, including securities not listed on any securities exchange.

If an underwriter or underwriters are utilized in the sale, we will execute an underwriting agreement with the underwriters at the time of sale to them and the names of the underwriters will be set forth in the applicable prospectus supplement, which will be used by the underwriters to make resales of the securities in respect of which this prospectus is delivered to the public. The obligations of underwriters to purchase securities will be subject to certain conditions precedent and the underwriters will be obligated to purchase all of the securities of a series if any are purchased.

Underwriters, dealers, agents and other persons may be entitled, under agreements that may be entered into with us, to indemnification against certain civil liabilities, including liabilities under the Securities Act, or to contribution with respect to payments that they may be required to make in respect thereof. Underwriters, dealers and agents may engage in transactions with, or perform services for, us in the ordinary course of business.

Except as indicated in the applicable prospectus supplement, the debt securities are not expected to be listed on a securities exchange, and any underwriters or dealers will not be obligated to make a market in debt securities. We cannot predict the activity or liquidity of any trading in the debt securities.

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LEGAL MATTERS

The legality of the debt securities offered by this prospectus will be passed upon by Perkins Coie LLP. If the securities are being distributed in an underwritten offering, certain legal matters will be passed upon for the underwriters by counsel identified in the related prospectus supplement.

EXPERTS

The consolidated financial statements of Costco Wholesale Corporation as of September 1, 2019 and September 2, 2018, and for the 52-week period ended September 1, 2019, the 52-week period ended September 2, 2018 and the 53-week period ended September 3, 2017, and management’s assessment of the effectiveness of internal control over financial reporting as of September 1, 2019 have been incorporated by reference herein in reliance upon the reports of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

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$4,000,000,000

$1,250,000,000 1.375% Senior Notes due 2027

$1,750,000,000 1.600% Senior Notes due 2030

$1,000,000,000 1.750% Senior Notes due 2032

Joint Book-Running Managers

Credit Suisse

BofA Securities

Citigroup

US Bancorp

HSBC

Drexel Hamilton

Guzman and Company

April 16, 2020