0001562565 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:C000248144Member 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:CashTransactionsRiskMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:FinancialServicesConcentrationMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:FluctuationOfNetAssetValueAndSharePriceMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:ForeignExposureMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:InterestRateChangesMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:IssuerSpecificChangesMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:LeverageRiskMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:PrepaymentMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member rr:RiskLoseMoneyMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member rr:RiskNotInsuredDepositoryInstitutionMember 2024-02-09 2024-02-09 0001562565 fmst:S000084018Member fmst:TradingIssuesMember 2024-02-09 2024-02-09 iso4217:USD pure 0001562565 false 2024-02-08 485BPOS 2024-02-08 N-1A Fidelity Merrimack Street Trust 2024-02-09 2024-02-09 Fund Summary Fund: Fidelity® Low Duration Bond ETF Investment Objective <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">Fidelity<sup style="font-size:75%;vertical-align:top">®</sup> Low Duration Bond ETF seeks to obtain a high level of current income consistent with preservation of capital. </div> Fee Table <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">The following table describes the fees and expenses that may be incurred </div><div style="margin-top:0pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;"> when you buy, hold, and sell shares of the fund.<span style="font-family:arial"><span style="font-weight:bold"></span></span><span style="font-family:arial"><span style="font-weight:bold"> You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table or example below.</span></span><span style="font-family:times new roman"> </span></div> Shareholder fees(fees paid directly from your investment) 0 Annual Operating Expenses(expenses that you pay each year as a % of the value of your investment) 0.0020 0 0.0000 0.0020 Based on estimated amounts for the current fiscal year. <div style="margin-top:0pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">This<span style="font-family:arial"><span style="font-weight:bold"> example</span></span><span style="font-family:times new roman"> helps compare the cost of investing in the fund with the cost of investing in other funds. </span></div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">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. </div><div style="margin-top:0pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;"> 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:</div> 20 64 Portfolio Turnover <div style="margin-top:2pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and </div><div style="margin-top:0pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;"> may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual operating expenses or in the example, affect the fund’s performance. </div> Principal Investment Strategies <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Normally investing at least 80% of assets in investment-grade debt securities (those of medium and high quality) of all types and repurchase agreements for those securities. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Normally maintaining a duration of 1 year or less. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Managing the fund to have similar overall interest rate risk to the Bloomberg US Treasury Bill: 6‑9 Months Index. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Normally maintaining a dollar-weighted average maturity of two years or less. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Allocating assets across different market sectors and maturities. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Investing more than 25% of total assets in the financial services industries. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Investing in domestic and foreign issuers. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Analyzing the credit quality of the issuer, security-specific features, current and potential future valuation, and trading opportunities to select investments. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives — such as swaps (interest rate, total return, and credit default), options, and futures contracts — and forward-settling securities, to adjust the fund’s risk exposure. </div> Principal Investment Risks <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Interest Rate Changes.</span></span><span style="font-family:times new roman"> Interest rate increases can cause the price of a debt security to decrease. </span></div> <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Foreign Exposure.</span></span><span style="font-family:times new roman"> Foreign markets can be more volatile than the U.S. market due to increased risks of adverse issuer, political, regulatory, market, or economic developments and can perform differently from the U.S. market. </span></div> <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Financial Services Concentration.</span></span><span style="font-family:times new roman"> Changes in government regulation and interest rates and economic downturns can have a significant negative effect on issuers in the financial services sector, including the price of their securities or their ability to meet their payment obligations. </span></div> <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Prepayment.</span></span><span style="font-family:times new roman"> The ability of an issuer of a debt security to repay principal prior to a security’s maturity can cause greater price volatility if interest rates change. </span></div> <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Issuer-Specific Changes.</span></span><span style="font-family:times new roman"> The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole. </span></div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">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 security to decrease. </div> <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Leverage Risk.</span></span><span style="font-family:times new roman"> Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly. </span></div> <div style="margin-top:0pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Fluctuation of Net Asset Value and Share Price.</span></span><span style="font-family:times new roman"> The net asset value per share (NAV) of the fund will generally fluctuate with changes in the market value of the fund’s holdings. The fund’s shares can be bought and sold in the secondary market at market prices. Disruptions to creations and redemptions, the existence of extreme market volatility or potential lack of an active trading market for the fund’s shares may result in the fund’s shares trading significantly above (at a premium) or below (at a discount) to NAV. </span></div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">Given the nature of the relevant markets for certain of the fund’s securities, shares may trade at a larger premium or discount to the NAV than shares of other ETFs. </div><div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">In addition, in stressed market conditions or periods of market disruption or volatility, the market for shares may become less liquid in response to deteriorating liquidity in the markets for the fund’s underlying portfolio holdings. </div> <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Trading Issues.</span></span><span style="font-family:times new roman"> There can be no assurance that an active trading market will be maintained. Market makers and Authorized Participants are not obligated to make a market in the fund’s shares or to submit purchase and redemption orders for creation units. In addition, trading may be halted, for example, due to market conditions. </span></div> <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">• <span style="font-family:arial"><span style="font-style:italic">Cash Transactions Risk.</span></span><span style="font-family:times new roman"> Unlike certain ETFs, the fund may effect some or all creations and redemptions using </span></div><div style="margin-top:0pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;"> cash, rather than in‑kind securities. As a result, an investment in the fund may be less tax‑efficient than an investment in an ETF that distributes portfolio securities entirely in‑kind. </div> An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You could lose money by investing in the fund. Performance <div style="margin-top:6pt;margin-bottom:0pt;font-size:10pt;font-family:times new roman;">Performance history will be available for the fund after the fund has been in operation for one calendar year.</div> Performance history will be available for the fund after the fund has been in operation for one calendar year. Based on estimated amounts for the current fiscal year.