0000917286 2021-11-26 2021-11-26 0000917286 qsk:NF0430FidelityGovernmentMoneyMarketFundClassSPro01Member qsk:S000007051Member 2021-11-26 2021-11-26 0000917286 qsk:NF0430FidelityGovernmentMoneyMarketFundClassSPro01Member qsk:S000007051Member qsk:C000232685Member 2021-11-26 2021-11-26 0000917286 qsk:NF0430FidelityGovernmentMoneyMarketFundClassSPro01Member qsk:S000007051Member qsk:C000019230Member 2021-11-26 2021-11-26 0000917286 qsk:NF0430FidelityGovernmentMoneyMarketFundClassSPro01Member qsk:S000007051Member qsk:ReturnBeforeTaxesMember qsk:C000019230Member 2021-11-26 2021-11-26 iso4217:USD pure 485BPOS 2021-04-30 false 0000917286 N-1A FIDELITY HEREFORD STREET TRUST 0.0001 0.0001 0.0001 0.0001 0.0001 0.0004 0.0051 0.0147 0.0184 0.0026 Fund Summary Fund/Class:Fidelity® Government Money Market Fund/S Investment Objective The fund seeks as high a level of current income as is consistent with preservation of capital and liquidity. Fee Table The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund. Shareholder fees 0 Annual Operating Expenses (expenses that you pay each year as a % of the value of your investment) 0.0025 0 0.0022 0.0047 -0.0005 0.0042 August 31, 2023 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 your shareholder 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: 43 142 254 583 Principal Investment Strategies Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. Principal Investment Risks 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. Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease. You could lose money by investing in the fund. Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the fund 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, have no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time. The fund will not impose a fee upon the sale of your shares, nor temporarily suspend your ability to sell shares if the fund's weekly liquid assets fall below 30% of its total assets because of market conditions or other factors. You could lose money by investing in the fund. Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the fund 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, have no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time. 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 Fidelity ® Government Money Market Fund, a class of shares of the fund, from year to year. Past performance (before and after taxes) is not an indication of future performance. Visit www.fidelity.com for more recent performance information. Performance history will be available for Class S after Class S has been in operation for one calendar year. The information illustrates the changes in the performance of Fidelity ® Government Money Market Fund, a class of shares of the fund, from year to year. Past performance (before and after taxes) is not an indication of future performance. www.fidelity.com Performance history will be available for Class S after Class S has been in operation for one calendar year. Year-by-Year Returns* Highest Quarter Return 0.0051 2019-06-30 Lowest Quarter Return 0.0000 2015-03-31 Year-to-Date Return 0.0000 2021-06-30 * The returns shown above are for Fidelity ® Government Money Market Fund, a class of shares of the fund that is not offered through this prospectus. Class S would have substantially similar annual returns to Fidelity ® Government Money Market Fund because the classes are invested in the same portfolio of securities. Class S returns would differ from Fidelity ® Government Money Market Fund's returns only to the extent that the classes do not have the same expenses. Average Annual Returns* Fidelity® Government Money Market Fund 0.0026 0.0082 0.0042 * The returns shown above are for Fidelity ® Government Money Market Fund, a class of shares of the fund that is not offered through this prospectus. Class S would have substantially similar annual returns to Fidelity ® Government Money Market Fund because the classes are invested in the same portfolio of securities. Class S returns would differ from Fidelity ® Government Money Market Fund's returns only to the extent that the classes do not have the same expenses. * The returns shown above are for Fidelity ® Government Money Market Fund, a class of shares of the fund that is not offered through this prospectus. Class S would have substantially similar annual returns to Fidelity ® Government Money Market Fund because the classes are invested in the same portfolio of securities. Class S returns would differ from Fidelity ® Government Money Market Fund's returns only to the extent that the classes do not have the same expenses. (a)Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Class S of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, 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 0.42% (the Expense Cap). If at any time during the current fiscal year expenses for Class S of 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 August 31, 2023 . 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. (b)In order to avoid a negative yield, FMR may reimburse expenses or waive fees of Class S of the fund. Any such waivers or expense reimbursement would be voluntary and could be discontinued at any time. There is no guarantee that Class S or the fund will be able to avoid a negative yield.