Calvert Responsible Index Series N-CSRSCertified semi-annual shareholder report (management investment company)

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As a Fund shareholder, you incur two types of costs: (1) transaction costs, including sales charges (loads) on purchases; and (2) ongoing costs, including management fees; distribution and/or service fees; and other Fund expenses. This Example is intended to help you understand your ongoing costs (in dollars) of Fund investing and to compare these costs with the ongoing costs of investing in other mutual funds. The Example is based on an investment of $1,000 invested at the beginning of the period and held for the entire period (October 1, 2023 to March 31, 2024).

The first section of the table below provides information about actual account values and actual expenses. You may use the information in this section, together with the amount you invested, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number in the first section under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

The second section of the table below provides information about hypothetical account values and hypothetical expenses based on the actual Fund expense ratio and an assumed rate of return of 5% per year (before expenses), which is not the actual Fund return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the Fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as sales charges (loads). Therefore, the second section of the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would be higher.

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See Notes to Financial Statements.

Calvert US Large-Cap Growth Responsible Index Fund (the Fund) is a diversified series of Calvert Responsible Index Series, Inc. (the Corporation). The Corporation is a Maryland corporation registered under the Investment Company Act of 1940, as amended (the 1940 Act), as an open-end management investment company. The investment objective of the Fund is to seek to track the performance of the Calvert US Large-Cap Growth Responsible Index, which measures the investment return of large-capitalization stocks.

The Fund offers three classes of shares. Class A shares are generally sold subject to a sales charge imposed at time of purchase. A contingent deferred sales charge of 0.25% may apply to certain redemptions of Class A shares for accounts for which no sales charge was paid, if redeemed within 12 months of purchase. Class I and Class R6 shares are sold at net asset value, are not subject to a sales charge and are sold only to certain eligible investors. Each class represents a pro rata interest in the Fund, but votes separately on class-specific matters and is subject to different expenses.

The Fund applies the accounting and reporting guidance in the Financial Accounting Standards Board (FASB) Accounting Standards Codification Topic 946, Financial Services – Investment Companies (ASC 946). Subsequent events, if any, through the date that the financial statements were issued have been evaluated in the preparation of the financial statements.

U.S. generally accepted accounting principles (U.S. GAAP) establishes a disclosure hierarchy that categorizes the inputs to valuation techniques used to value assets and liabilities at measurement date. These inputs are summarized in the three broad levels listed below:

Level 1 - quoted prices in active markets for identical securities

Level 2 - other significant observable inputs (including quoted prices for similar securities, interest rates, prepayment speeds, credit risk, etc.)

Level 3 - significant unobservable inputs (including the Fund’s own assumptions in determining the fair value of investments)

The inputs or methodologies used for valuing securities are not necessarily an indication of the risk associated with investing in those securities.

Valuation techniques used to value the Fund’s investments by major category are as follows:

The values assigned to fair value investments are based on available information and do not necessarily represent amounts that might ultimately be realized. Further, due to the inherent uncertainty of valuations of such investments, the fair values may differ significantly from the values that would have been used had an active market existed, and the differences could be material.

The following table summarizes the market value of the Fund's holdings as of March 31, 2024, based on the inputs used to value them:

Level 3 assets at the beginning and/or end of the period in relation to net assets were not significant and accordingly, a reconciliation of Level 3 assets for the six months ended March 31, 2024 is not presented.

Management has analyzed the Fund's tax positions taken for all open federal income tax years and has concluded that no provision for federal income tax is required in the Fund's financial statements. A Fund's federal tax return is subject to examination by the Internal Revenue Service for a period of three years from the date of filing.

The investment advisory fee is earned by Calvert Research and Management (CRM), an indirect, wholly-owned subsidiary of Morgan Stanley, as compensation for investment advisory services rendered to the Fund. The investment advisory fee is computed at the annual rate of 0.12% of the Fund’s average daily net assets and is payable monthly. For the six months ended March 31, 2024, the investment advisory fee amounted to $339,816.

The Fund may invest in a money market fund, the Institutional Class of the Morgan Stanley Institutional Liquidity Funds - Government Portfolio (the “Liquidity Fund”), an open-end management investment company managed by Morgan Stanley Investment Management Inc., a wholly-owned subsidiary of Morgan Stanley. The investment advisory fee paid by the Fund is reduced by an amount equal to its pro rata share of the advisory and administration fees paid by the Fund due to its investment in the Liquidity Fund. For the six months ended March 31, 2024, the investment advisory fee paid was reduced by $966 relating to the Fund’s investment in the Liquidity Fund.

CRM has agreed to reimburse the Fund’s operating expenses to the extent that total annual operating expenses (relating to ordinary operating expenses only and excluding expenses such as brokerage commissions, acquired fund fees and expenses of unaffiliated funds, borrowing costs, taxes or litigation expenses) exceed 0.49%, 0.24% and 0.21% for Class A, Class I and Class R6, respectively, of such class’s average daily net assets. The expense reimbursement agreement with CRM may be changed or terminated after February 1, 2025. For the six months ended March 31, 2024, CRM waived or reimbursed expenses of $424,878.

The administrative fee is earned by CRM as compensation for administrative services rendered to the Fund. The fee is computed at an annual rate of 0.12% of the Fund’s average daily net assets attributable to Class A, Class I and Class R6 and is payable monthly. For the six months ended March 31, 2024, CRM was paid administrative fees of $339,816.

The Fund has in effect a distribution plan for Class A shares (Class A Plan) pursuant to Rule 12b-1 under the 1940 Act. Pursuant to the Class A Plan, the Fund pays Eaton Vance Distributors, Inc. (EVD), an affiliate of CRM and the Fund’s principal underwriter, a distribution and service fee of 0.25% per annum of its average daily net assets attributable to Class A shares for distribution services and facilities provided to the Fund by EVD, as well as for personal services and/or the maintenance of shareholder accounts. Distribution and service fees paid or accrued for the six months ended March 31, 2024 amounted to $113,426 for Class A shares.

The Fund was informed that EVD received $15,199 as its portion of the sales charge on sales of Class A shares for the six months ended March 31, 2024.

Eaton Vance Management (EVM), an affiliate of CRM, provides sub-transfer agency and related services to the Fund pursuant to a Sub-Transfer Agency Support Services Agreement. For the six months ended March 31, 2024, sub-transfer agency fees and expenses incurred to EVM amounted to $8,518 and are included in transfer agency fees and expenses on the Statement of Operations.

Each Director of the Fund who is not an employee of CRM or its affiliates receives an annual fee of $225,000 ($214,000 prior to January 1, 2024), an annual Committee fee ranging from $8,500 to $16,500 depending on the Committee, and may receive a fee of $10,000 for special meetings. The Board chair receives an additional $40,000 annual fee, Committee chairs receive an additional $15,000 annual fee and the special equities liaison receives an additional $2,500 annual fee. Eligible Directors may participate in a Deferred Compensation Plan (the Plan). Amounts deferred under the Plan are treated as though equal dollar amounts had been invested in shares of the Fund or other Calvert funds selected by the Directors. The Fund purchases shares of the funds selected equal to the dollar amounts deferred under the Plan, resulting in an asset equal to the deferred compensation liability. Obligations of the Plan are paid solely from the Fund's assets. Directors’ fees are allocated to each of the Calvert funds served. Salaries and fees of officers and Directors of the Fund who are employees of CRM or its affiliates are paid by CRM.

During the six months ended March 31, 2024, the cost of purchases and proceeds from sales of investments, other than short-term securities, were $65,894,241 and $39,157,869, respectively.

At September 30, 2023, the Fund, for federal income tax purposes, had deferred capital losses of $9,163,602 which would reduce the Fund’s taxable income arising from future net realized gains on investment transactions, if any, to the extent permitted by the Internal Revenue Code, and thus would reduce the amount of distributions to shareholders, which would otherwise be necessary to relieve the Fund of any liability for federal income or excise tax. The deferred capital losses are treated as arising on the first day of the Fund’s next taxable year, can be carried forward for an unlimited period, and retain the same short-term or long-term character as when originally deferred. Of the deferred capital losses at September 30, 2023, $5,888,514 are short-term and $3,275,088 are long-term.

The cost and unrealized appreciation (depreciation) of investments of the Fund at March 31, 2024, as determined on a federal income tax basis, were as follows:

To generate additional income, the Fund may lend its securities pursuant to a securities lending agency agreement with State Street Bank and Trust Company (SSBT), the securities lending agent. Security loans are subject to termination by the Fund at any time and, therefore, are not considered illiquid investments. The Fund requires that the loan be continuously collateralized by either cash or securities in an amount at least equal to the market value of the securities on loan. The market value of securities loaned is determined daily and any additional required collateral is delivered to the Fund on the next business day. Cash collateral is generally invested in a money market fund registered under the 1940 Act that is managed by an affiliate of SSBT. Any gain or loss in the market price of the loaned securities that might occur and any interest earned or dividends declared during the term of the loan would accrue to the account of the Fund. Income earned on the investment of collateral, net of broker rebates and other expenses incurred by the securities lending agent, is split between the Fund and the securities lending agent based on agreed upon contractual terms. Non-cash collateral, if any, is held by the lending agent on behalf of the Fund and cannot be sold or re-pledged by the Fund; accordingly, such collateral is not reflected in the Statement of Assets and Liabilities.

The risks associated with lending portfolio securities include, but are not limited to, possible delays in receiving additional collateral or in the recovery of the loaned securities, possible loss of rights to the collateral should the borrower fail financially, as well as risk of loss in the value of the collateral or the value of the investments made with the collateral. The securities lending agent shall indemnify the Fund in the case of default of any securities borrower.

At March 31, 2024, the total value of securities on loan was $70,094 and the total value of collateral received was $73,697, comprised of cash of $3,216 and U.S. government and/or agencies securities of $70,481.

The following table provides a breakdown of securities lending transactions accounted for as secured borrowings, the obligations by class of collateral pledged, and the remaining contractual maturity of those transactions as of March 31, 2024.

The carrying amount of the liability for deposits for securities loaned at March 31, 2024 approximated its fair value. If measured at fair value, such liability would have been considered as Level 2 in the fair value hierarchy (see Note 1A) at March 31, 2024.

The Fund participates with other portfolios and funds managed by EVM and its affiliates, including CRM, in a $650 million unsecured revolving line of credit agreement with a group of banks, which is in effect through October 22, 2024. In connection with the renewal of the agreement on October 24, 2023, the borrowing limit was decreased from $725 million. Borrowings are made by the Fund solely for temporary purposes related to redemptions and other short-term cash needs. Interest is charged to the Fund based on its borrowings at an amount above either the Secured Overnight Financing Rate (SOFR) or Federal Funds rate. In addition, a fee computed at an annual rate of 0.15% on the daily unused portion of the line of credit is allocated among the participating portfolios and funds at the end of each quarter. In connection with the renewal of the agreement in October 2023, an arrangement fee of $150,000 was incurred that was allocated to the participating portfolios and funds. Because the line of credit is not available exclusively to the Fund, it may be unable to borrow some or all of its requested amounts at any particular time.

The Fund had no borrowings outstanding pursuant to its line of credit at March 31, 2024. The Fund did not have any significant borrowings or allocated fees during the six months ended March 31, 2024.

At March 31, 2024, the value of the Fund’s investment in funds that may be deemed to be affiliated was $1,371,938, which represents 0.2% of the Fund’s net assets. Transactions in such investments by the Fund for the six months ended March 31, 2024 were as follows:

The Corporation may issue its shares in one or more series (such as the Fund). The authorized shares of the Fund consist of 75,000,000 common shares, $0.01 par value, for each Class.

Transactions in capital shares were as follows:

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As a Fund shareholder, you incur two types of costs: (1) transaction costs, including sales charges (loads) on purchases; and (2) ongoing costs, including management fees; distribution and/or service fees; and other Fund expenses. This Example is intended to help you understand your ongoing costs (in dollars) of Fund investing and to compare these costs with the ongoing costs of investing in other mutual funds. The Example is based on an investment of $1,000 invested at the beginning of the period and held for the entire period (October 1, 2023 to March 31, 2024).

The first section of the table below provides information about actual account values and actual expenses. You may use the information in this section, together with the amount you invested, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number in the first section under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

The second section of the table below provides information about hypothetical account values and hypothetical expenses based on the actual Fund expense ratio and an assumed rate of return of 5% per year (before expenses), which is not the actual Fund return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the Fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as sales charges (loads). Therefore, the second section of the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would be higher.

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