0000035315 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:MunicipalMarketVolatilityMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:InterestRateChangesMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:IncomeRiskMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:FloatingNavMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:ForeignExposureMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:IssuerSpecificChangesMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member oef:RiskLoseMoneyMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member oef:RiskMoneyMarketFundMayNotPreserveDollarMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member oef:RiskNotInsuredDepositoryInstitutionMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member oef:RiskMoneyMarketFundSponsorMayNotProvideSupportMember 2026-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2019-01-01 2019-12-31 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2020-01-01 2020-12-31 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2021-01-01 2021-12-31 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2022-01-01 2022-12-31 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2023-01-01 2023-12-31 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2024-01-01 2024-12-31 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2025-01-01 2025-12-31 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2025-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2021-05-30 2026-05-30 0000035315 fmr:FidelitySAIMunicipalMoneyMarketFund-PROMember fmr:S000059873Member fmr:C000195869Member 2018-05-30 2026-05-30 iso4217:USD pure 485BPOS 2026-05-30 false 0000035315 N-1A Fidelity Salem Street Trust Fund Summary Fund: Fidelity® SAI Municipal Money Market Fund Investment Objective Fidelity® SAI Municipal Money Market Fund seeks as high a level of interest income exempt from federal income tax as is consistent with liquidity and stability of principal. Fee Table The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. Shareholder fees 0 Annual Operating Expenses 0.0014 0 0.0015 0.0029 -0.0022 0.0007 2027-07-31 This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated: 7 63 133 339 Principal Investment Strategies Normally investing in municipal money market securities. Normally investing at least 80% of assets in municipal securities whose interest is exempt from federal income tax (but may be subject to the federal alternative minimum tax). Municipal money market securities are high-quality, short-term debt securities that pay a fixed, variable, or floating interest rate, and include variable rate demand notes, commercial paper, and municipal notes. Municipal securities are issued to raise money for a variety of public and private purposes, including general financing for state and local governments, financing for eligible non-profit organizations, or financing for a specific project or public facility. Potentially investing up to 20% of assets in securities subject to state and/or federal income tax. Potentially investing more than 25% of total assets in municipal securities that finance similar types of projects. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. Investing in Fidelity's Central funds (specialized investment vehicles used by Fidelity® funds to invest in particular security types or investment disciplines). Although the fund is a money market fund, it will price and transact at a "floating" net asset value per share (NAV) that will fluctuate based on changes in the value of the fund's investments. Municipal Market Volatility. The municipal market is volatile and can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease. Income Risk. A low or negative interest rate environment can adversely affect the fund's yield. Floating NAV. The fund does not maintain a constant NAV per share of $1.00. The value of the fund's shares will be calculated to four decimal places and will vary as a result of changes in the value of the securities in which the fund invests. Foreign Exposure. Entities providing credit support or a maturity-shortening structure that are located in foreign countries can be affected by adverse political, regulatory, market, or economic developments in those countries . Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support (such as guarantees) or a maturity-shortening structure (such as demand and put features) for a security can cause the price of a money market security to decrease.   You could lose money by investing in the fund.   Because the share price of the fund will fluctuate, when you sell your shares, they may be worth more or less than what you originally paid for them. The fund may impose a fee upon the sale of your shares.   The fund generally must impose a fee when net sales of fund shares exceed certain levels. An investment in the fund is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Fidelity Investments and its affiliates, the fund's sponsor, is not required to reimburse the fund for losses, and you should not expect that the sponsor will provide financial support to the fund at any time, including during periods of market stress. Performance The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information. The information illustrates the changes in the performance of the fund's shares from year to year. Past performance is not an indication of future performance. www.fidelity.com Year-by-Year Returns 0.0144 0.0053 0.0002 0.0110 0.0340 0.0338 0.0266    Highest Quarter Return 0.0095 2024-06-30    Lowest Quarter Return -0.0002 2022-03-31    Year-to-Date Return 0.0046 2026-03-31 Average Annual Returns Fidelity® SAI Municipal Money Market Fund 0.0266 0.0210 0.0173 2018-01-11 A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, proxy and shareholder meeting expenses, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.07% (the Expense Cap). If at any time during the current fiscal year expenses for the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through July 31, 2027 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date. A From January 11, 2018 .