Money Market Funds Guide 2026: Government vs. Prime vs. Tax-Exempt, SEC 2024 Reforms, Yields, Tax Treatment & How They Compare to HYSAs, CDs, and T-Bills

What Is a Money Market Fund and Why It Matters in 2026

A money market fund (MMF) is an open-end mutual fund, registered under the Investment Company Act of 1940 and regulated by the U.S. Securities and Exchange Commission, that invests exclusively in short-duration, high-quality debt instruments — Treasury bills, repurchase agreements, federal agency discount notes, commercial paper, certificates of deposit, and short-term municipal notes. The fund's overarching objective is to deliver income that closely tracks short-term interest rates while preserving each shareholder's principal at a stable $1.00 per-share price (or, for certain institutional categories, at a transparent floating net asset value). Because the underlying holdings have weighted average maturities measured in weeks rather than years, MMFs are universally classified as cash-equivalent investments rather than bond investments. The SEC's investor.gov glossary defines MMFs as a special type of mutual fund "that limits its investments to short-term securities," distinguishing them from longer-duration bond funds and equity funds.[1, 2]

It is critical at the outset to distinguish a money market fund from a money market account, because the two products are routinely confused in everyday conversation but differ in nearly every legal and economic respect. A money market deposit account (MMDA) is a bank product — a savings deposit, insured by the FDIC up to $250,000 per depositor per bank per ownership category, that pays an interest rate set by the issuing bank. A money market fund, by contrast, is an investment product — a mutual fund whose shares fluctuate (within tight regulatory limits) with the value of its underlying portfolio, is not insured by any government agency, and pays a market-determined yield that adjusts daily as the underlying instruments mature and are replaced. The Consumer Financial Protection Bureau states the distinction explicitly: "A money market mutual fund account is considered an investment, and it is not a savings or checking account." Confusing the two is one of the most common — and most expensive — mistakes retail investors make.[17, 15]

Money market funds matter to the 2026 investor more than at almost any other moment in recent memory because, after the Federal Reserve's 2022–2023 rate-hiking cycle, MMF yields jumped from near zero to multi-decade highs, and total industry assets reached record levels. According to the Investment Company Institute's weekly money market fund statistics, total U.S. money market fund assets exceed $7 trillion as of early 2026 — an unprecedented figure that reflects the migration of cash out of low-yielding bank deposits and into higher-yielding MMFs. For an investor sitting on cash that they would otherwise leave in a checking account or low-yield savings account, the difference between a 0.05% bank yield and a 4%-plus MMF yield represents thousands of dollars per year on a $50,000 balance. Understanding how MMFs work, which type to buy, and how they are taxed is therefore one of the highest-leverage financial decisions any saver can make in the current rate environment. For context on how short-term rates connect to broader Federal Reserve policy, our guide to how the Federal Reserve sets interest rates walks through the full transmission mechanism.[11, 7]

How Money Market Funds Work: NAV, Holdings, and Distribution Mechanics

Every U.S. money market fund operates under a single, highly prescriptive SEC regulation: Rule 2a-7 of the Investment Company Act of 1940. This rule constrains what an MMF may hold, how long the average remaining maturity of its holdings may be, how much liquidity it must keep on hand at all times, and how it must price its shares. The two most important Rule 2a-7 numerical limits are the weighted average maturity (WAM), which cannot exceed 60 days, and the weighted average life (WAL), which cannot exceed 120 days. WAM measures the sensitivity of the fund's portfolio to changes in interest rates, while WAL measures sensitivity to credit spreads. By keeping both numbers very low, Rule 2a-7 ensures that the fund's share price moves only minimally even when rates or spreads shift sharply — the foundation of the stable $1.00 NAV that retail investors expect.[1, 4]

The instruments inside a money market fund vary by type but share three key characteristics: very short remaining maturities, very high credit quality (typically the highest two short-term rating tiers, A-1/P-1 or equivalent), and deep liquidity. The most common holdings are Treasury bills (short-duration U.S. government debt detailed on TreasuryDirect), repurchase agreements (repos) collateralized by Treasuries or agency securities, federal agency discount notes issued by entities such as Fannie Mae and Freddie Mac, commercial paper (CP) issued by highly rated corporations and financial institutions, negotiable certificates of deposit (CDs) issued by domestic and foreign banks, and short-term municipal notes for tax-exempt funds. The fund's portfolio manager rolls these holdings continuously: as instruments mature each day, the proceeds are reinvested at prevailing market rates, which is precisely why an MMF's yield adjusts so quickly to changes in the federal funds rate or other short-term benchmarks. The Office of Financial Research's Money Market Fund Monitor provides interactive visualizations of these holdings broken down by fund category and instrument type.[21, 14, 4]

A retail money market fund accrues income to shareholders daily and pays it out as a monthly dividend. Each business day, the fund's portfolio accountant calculates the net interest income earned by the underlying holdings, divides it by the number of shares outstanding, and credits each shareholder's account with that day's share of income. At the end of the month, the accumulated daily accruals are paid out either in cash or, far more commonly, as additional fund shares purchased at the same $1.00 stable NAV — automatic reinvestment that compounds the yield over time. This daily-accrual, monthly-distribution structure is fundamentally different from a high-yield savings account, where interest typically accrues daily but is only credited monthly without compounding within the period. To project how a stream of monthly MMF distributions compounds over years of holding, our guide to compound interest explains the underlying math, and the calculator below the article lets you model the actual numbers for any starting balance and yield.[1, 4]

The Three Types: Government, Prime, and Tax-Exempt Money Market Funds

Under SEC Rule 2a-7, every money market fund must classify itself into one of three categories, and each category has materially different holdings, yields, tax treatment, and risk profiles. Choosing the right category is the single most important decision a retail MMF investor makes, far more important than choosing among individual funds within a category. The three categories are government (sometimes called "treasury" or "U.S. government" funds), prime (sometimes called "general purpose" funds), and tax-exempt (sometimes called "municipal" or "muni" funds). Within each category, funds are further sub-classified as either retail (sold only to natural persons) or institutional (open to corporations, retirement plans, and other entities), a distinction that became even more consequential after the 2024 SEC reforms covered in the next section. The OFR Money Market Fund Monitor tracks total assets and portfolio composition for all three categories on a continuously updated basis.[13, 14]

Government money market funds are required by Rule 2a-7 to invest at least 99.5% of their total assets in cash, U.S. government securities (Treasury bills, notes, and agency obligations), and repurchase agreements collateralized solely by cash or U.S. government securities. The remaining 0.5% provides minimal flexibility for short-term operational needs. Government MMFs maintain a stable $1.00 NAV in all market conditions and, critically, are exempt from the mandatory liquidity fees imposed on other categories under the 2024 SEC reforms. They are the safest category by every objective measure — credit risk is essentially zero because the holdings are backed by the full faith and credit of the U.S. government, liquidity risk is minimized by the high-quality collateral, and the stable NAV protects against any pricing surprises. Government funds typically yield slightly less than prime funds (10–30 basis points in normal market conditions) because they hold lower-yielding government paper rather than corporate paper. Many brokerages — including Vanguard, Fidelity, Schwab, and others — offer government MMFs as the default sweep position for cash sitting in brokerage accounts.[14, 5]

Prime money market funds invest in a broader universe of high-quality, short-term debt that includes commercial paper issued by corporations, negotiable certificates of deposit issued by domestic and foreign banks, banker's acceptances, repurchase agreements with non-government collateral, and Eurodollar deposits — alongside whatever government securities the manager chooses to hold for liquidity. The trade-off compared to government funds is straightforward: prime funds offer a modest yield premium (historically 10–40 basis points) in exchange for taking on credit risk to corporate and bank issuers. Retail prime funds maintain a stable $1.00 NAV like government funds, but institutional prime funds have been required since 2014 SEC reforms to use a floating NAV that reprices throughout the day, and the 2024 reforms further imposed mandatory liquidity fees on institutional prime funds when net redemptions exceed certain thresholds. For most retail investors, retail prime funds provide a sensible way to capture extra yield without any meaningful operational difference compared to government funds — the credit risk is real but historically small, and the funds are still subject to the full Rule 2a-7 quality and maturity constraints.[14, 4]

Tax-exempt money market funds (also called municipal MMFs) invest in short-term obligations issued by U.S. state and local governments and their agencies — short-term municipal notes, variable-rate demand obligations (VRDOs), tax-exempt commercial paper, and put bonds with reset dates. The headline feature is that the interest paid by these instruments is exempt from federal income tax under the Internal Revenue Code, and a fund holding only obligations from a single state will also be exempt from that state's income tax for residents. Single-state tax-exempt MMFs are common in high-tax states such as California, New York, New Jersey, and Massachusetts, where the combined federal-and-state tax savings can make their pre-tax-equivalent yield competitive with prime funds even though their nominal yield is lower. The catch is that some tax-exempt MMFs hold private-activity bonds whose interest, while federally tax-exempt for regular tax purposes, is included in the alternative minimum tax base; investors subject to AMT should select funds that explicitly avoid private-activity bonds. Detailed taxation rules are spelled out in IRS Publication 550 — Investment Income and Expenses.[18, 14]

The 2024 SEC Money Market Fund Reforms: What Changed and Why It Matters

In July 2023, the U.S. Securities and Exchange Commission adopted final amendments to Rule 2a-7 in response to the dislocations that money market funds experienced in March 2020 during the COVID-19 market stress, when several institutional prime funds saw rapid outflows that approached the conditions for triggering pre-existing fee-and-gate rules. The amendments — most of which had compliance dates phased between April and October 2024 — represent the most significant overhaul of money market fund regulation since the 2014 reforms that introduced floating NAV for institutional non-government funds. As described in FINRA's investor guidance on money market funds, the post-2024 framework is designed to make MMFs more resilient under stress while preserving their utility as cash management vehicles for retail and institutional investors alike.[4]

The 2024 reforms made four substantive changes to how money market funds operate. First, the SEC removed the regulatory link between weekly liquid asset thresholds and the imposition of liquidity fees and redemption gates that had been built into Rule 2a-7 in 2010 and 2014. Under the prior framework, if a fund's weekly liquid assets fell below 30%, the fund's board had discretion to impose fees or gates, and was required to consider doing so below 10% — a structure that, in March 2020, was widely blamed for accelerating outflows because investors raced to redeem before fees could be triggered. The post-2024 framework eliminates discretionary fees and gates tied to liquid asset thresholds entirely. Second, the SEC raised the daily liquid asset minimum from 10% to 25% of total assets and the weekly liquid asset minimum from 30% to 50% — a substantial increase in the buffer of cash and near-cash that every fund must hold against a redemption shock.[1, 13]

Third, the SEC introduced mandatory liquidity fees for institutional prime and institutional tax-exempt money market funds whenever daily net redemptions exceed 5% of fund assets. The fee is calibrated to the actual cost of providing liquidity at that moment, which is intended to make the fee a genuine pricing mechanism (each redeeming shareholder bears their share of the cost their redemption imposes on remaining shareholders) rather than a punitive deterrent. Importantly, this mandatory fee applies only to institutional prime and institutional tax-exempt funds — retail prime, retail tax-exempt, and all government funds (both retail and institutional) are exempt. Fourth, the SEC discarded the swing-pricing approach it had previously proposed and instead adopted the mandatory liquidity fee as the primary tool for allocating the cost of large redemptions. For practical purposes, this means that retail investors holding government MMFs or retail prime MMFs at a brokerage face essentially no operational change from the 2024 reforms; the changes affect institutional cash managers and fund operators much more directly.[13, 4]

MMF Yields Explained: 7-Day SEC Yield, Federal Funds Rate, and How to Compare Funds

The yield you see quoted on a money market fund's fact sheet is almost always the 7-day SEC yield, a standardized calculation that the SEC requires every MMF to disclose so that investors can compare funds on an apples-to-apples basis. The 7-day SEC yield is derived by taking the net income earned by the fund over the prior seven days, subtracting the fund's expenses, annualizing the result on a simple-interest basis, and reporting it as a single number. Because the calculation methodology is uniform across all MMFs, the 7-day SEC yield is the only fair way to compare yields across funds — never compare a 7-day SEC yield from one fund to a "distribution yield" or "trailing 12-month yield" from another, because those metrics use different denominators and time windows. The SEC investor.gov glossary provides the official definition for retail use.[3]

The yield on a money market fund tracks the federal funds rate with remarkable precision because the Federal Reserve's open-market operations directly determine the rates at which MMFs reinvest their maturing holdings each day. When the Federal Open Market Committee (FOMC) raises its target range for the federal funds rate, repo rates rise within hours, T-bill auction yields rise within days, and MMF 7-day yields catch up within weeks. When the FOMC cuts, the same chain of transmission runs in reverse. The FOMC publishes its target range and meeting minutes on the Federal Reserve's FOMC page, and the daily Federal Reserve H.15 Selected Interest Rates report publishes the actual effective federal funds rate alongside Treasury yields for every standard maturity. Together, these two pages let you predict where MMF yields will be over the next quarter with reasonable accuracy. The mechanics of how the Fed actually executes monetary policy through open-market operations are detailed on the Federal Reserve's Open Market Operations page.[6, 5, 8, 7]

When you compare two MMFs with similar 7-day SEC yields, the next decision factor is the expense ratio, because the SEC yield is reported net of expenses. A government MMF charging 11 basis points and yielding 4.30% has the same gross income as a competitor charging 41 basis points and yielding 4.00% — the difference is entirely a fee handed to the fund company. Across the industry, expense ratios for retail money market funds range from roughly 10 basis points (for the largest, lowest-cost providers like Vanguard, Fidelity, and Schwab) up to 60 or 70 basis points for smaller or more specialized funds. Over a $50,000 cash position held for five years, a 30-basis-point fee differential adds up to roughly $750 in expenses, with no compensating benefit because all government MMFs hold essentially identical underlying portfolios. The lesson: among similar MMFs in the same category at the same brokerage, always pick the lowest expense ratio. To project how that fee differential compounds over a longer holding period, our guide to investment fees and expense ratios walks through the math in detail.[10, 9]

Tax Treatment: How Money Market Fund Distributions Are Taxed in 2026

For tax purposes, distributions from a money market fund are reported to the IRS on Form 1099-DIV as either ordinary dividends or exempt-interest dividends, depending on the type of fund. Government MMFs and prime MMFs distribute ordinary dividends, which are taxed at the shareholder's ordinary federal income tax rate — the same rate that applies to wages, interest from savings accounts, and other forms of unearned income. These distributions are not qualified dividends, so they do not benefit from the lower 0%/15%/20% qualified dividend tax rates. IRS Tax Topic 404 explains the distinction between ordinary and qualified dividends, and detailed reporting rules are found in IRS Publication 550 — Investment Income and Expenses.[19, 18]

There is, however, an important and frequently overlooked nuance for government money market funds: a portion of the dividends is typically attributable to interest from direct U.S. Treasury obligations, which is exempt from state and local income tax under federal law (31 U.S.C. § 3124). At the end of each year, fund companies publish a "U.S. government obligation percentage" — sometimes called the "Treasury obligation factor" — that tells shareholders what share of their distributions qualifies for the state-tax exemption. For a fund that holds 75% Treasury bills and 25% government repos, the percentage might be around 60–70% depending on the year, meaning that residents of states with income tax effectively pay state tax only on the prime-equivalent portion of their distribution. This can be worth tens of basis points in after-tax yield for residents of high-tax states. For most retail brokerages, the U.S. government obligation percentage is reported annually with the 1099-DIV mailing, and the calculation must be entered manually in tax-preparation software because brokerage 1099-DIVs do not pre-apply the state exemption. For broader context on tax-efficient placement of cash and bond holdings across taxable and tax-advantaged accounts, our guide to tax-efficient investing walks through the framework.[18, 23]

For tax-exempt money market funds, distributions are reported on Form 1099-DIV as exempt-interest dividends in Box 12, and they are excluded from federal taxable income — full stop. If the fund is a single-state fund (a "California fund," "New York fund," etc.) and you are a resident of that state, your home state's share of the distributions is also exempt from your state income tax. The trade-off, of course, is that tax-exempt funds offer lower nominal yields than taxable funds. To compare them on an apples-to-apples basis, calculate the tax-equivalent yield (TEY) using the formula: TEY = Tax-Exempt Yield ÷ (1 − Marginal Tax Rate). If you are in the 32% federal bracket and a tax-exempt MMF yields 3.0%, the tax-equivalent yield is 3.0% ÷ (1 − 0.32) = 4.41% — meaning a taxable MMF would need to yield more than 4.41% to leave you with the same after-tax income. If you live in a state with high income tax, add the state rate to the marginal rate when comparing single-state tax-exempt funds. For most investors below the 24% federal bracket, taxable funds win after taxes; above the 32% bracket, single-state tax-exempt funds usually win in high-tax states.[18, 19]

MMFs vs. High-Yield Savings, CDs, and Treasury Bills: Choosing the Right Cash Vehicle

For a saver looking at the universe of cash management options in 2026, the four practical choices are money market funds, high-yield savings accounts (HYSAs), certificates of deposit (CDs), and direct Treasury bills purchased through TreasuryDirect or a brokerage. Each has its own combination of yield, liquidity, insurance coverage, tax treatment, minimum investment, and operational complexity. The single most important distinction — and the source of most beginner confusion — is the type of insurance: HYSAs and CDs at FDIC-member banks are insured up to $250,000 per depositor per institution per ownership category by the Federal Deposit Insurance Corporation; MMFs are not FDIC-insured, but they are protected by the Securities Investor Protection Corporation (SIPC) against the failure of the brokerage holding the shares (up to $500,000 in securities and $250,000 in cash). It is critical to understand that SIPC protection covers brokerage failure, not market loss — if the underlying MMF holdings lose value, SIPC does not reimburse the loss.[15, 16]

On yield, in normal market conditions all four vehicles converge toward the federal funds rate, but with consistent ordering: government MMFs and Treasury bills typically yield within 5–15 basis points of each other, prime MMFs add another 10–30 basis points of credit spread, the best HYSAs offered by online banks like Marcus, Ally, Discover, and Synchrony are competitive with government MMFs, and CDs offer a yield premium of perhaps 25–75 basis points in exchange for committing capital for a fixed term. On liquidity, MMFs and HYSAs both allow same-day or next-day access to your cash, while CDs typically charge an early-withdrawal penalty equal to several months of interest, and direct Treasury bills must be held to maturity (or sold on the secondary market through a brokerage). On tax treatment, government MMFs and direct Treasury bills are partially or fully exempt from state and local income tax — a meaningful advantage for residents of high-tax states. HYSAs and prime MMFs offer no state-tax advantage. Tax-exempt MMFs are exempt from federal income tax but typically yield less. For an in-depth comparison of where to park your emergency cash specifically, our emergency fund guide walks through all four options with practical recommendations.[15, 21]

A practical decision framework for 2026: if your priority is maximum simplicity and FDIC insurance under $250,000, choose a top-tier HYSA at an online bank — the yield gap to MMFs is small, the operational experience is identical to a checking account, and the federal insurance is both ironclad and free. If your priority is capturing the highest possible after-tax yield and you already have a brokerage account, choose a low-cost government MMF at the same brokerage as your default sweep position; if you live in a high-tax state, prefer one with a high U.S. government obligation percentage. If you want state-tax exemption with absolute credit safety and your cash needs are predictable, build a short rolling ladder of direct Treasury bills (4-week, 8-week, 13-week) — our Treasury securities investing guide walks through the ladder mechanics. If you can commit to a fixed term and want a yield premium, brokered CDs offer the highest yield with FDIC insurance, but only if you accept the loss of liquidity and the complexity of multiple maturity dates.[20, 15]

Risks, History, and How to Choose a Money Market Fund — Plus FAQs

Despite their reputation for safety, money market funds are not risk-free, and any honest assessment must account for two historical events when MMFs "broke the buck" — the industry term for an MMF whose share price falls below the $1.00 stable NAV. The first such event was the Community Bankers U.S. Government Money Market Fund in September 1994, which broke the buck due to losses on derivatives positions tied to interest-rate exposure that exceeded what the fund's portfolio could absorb. The fund was liquidated and shareholders received approximately $0.96 per share — a 4% loss on what they had been led to believe was a cash-equivalent investment. The second and far more consequential event was the Reserve Primary Fund in September 2008, which broke the buck after taking losses on commercial paper issued by Lehman Brothers when the investment bank filed for bankruptcy. Reserve Primary's collapse triggered a broader run on prime money market funds that the Treasury Department had to backstop with a temporary guarantee program — the trauma that ultimately led to the 2010, 2014, and 2024 SEC reforms. Research on the systemic implications of these events is collected by the Federal Reserve Bank of New York's Liberty Street Economics blog.[24, 4]

Two important caveats temper the implications of these historical events for a 2026 retail investor. First, in both cases the actual loss to shareholders was limited (4% in 1994, less than 1% in 2008 after the Treasury's guarantee program took effect), and in essentially every other case where an MMF has experienced stress, the fund's sponsor has voluntarily injected capital to keep the NAV at $1.00 — a practice known as sponsor support. Second, the post-2010, post-2014, and post-2024 regulatory reforms have substantially reduced the probability of a repeat by raising liquidity requirements, eliminating gates and discretionary fees that incentivized runs, and forcing institutional prime funds onto a floating NAV that prices credit risk transparently. The ICI 2024 Investment Company Fact Book documents how the industry's composition has shifted toward lower-risk government funds and away from prime funds in the years since each successive reform. For a 2026 retail investor holding a major brokerage's government MMF, the realistic risk of a "broken buck" event over any reasonable horizon is extremely small — close enough to zero that it should not influence the decision to use a government MMF as a cash management tool, though it remains nonzero, which is why MMFs are not classified as deposit accounts.[12, 24]

A practical buying checklist for retail investors choosing an MMF in 2026: (1) Pick the category first — government for default safety and state-tax efficiency, prime for a small yield boost if you tolerate corporate credit risk, tax-exempt only if you are in the 32% federal bracket or higher and live in a high-tax state. (2) At the same brokerage, pick the lowest-expense-ratio fund within the chosen category — a 10–15 basis-point fund will beat a 50-basis-point fund of the same category over any meaningful holding period. (3) Verify that the fund is offered as a brokerage core position (sweep) if you plan to use it for daily cash, or as a separately purchasable mutual fund if you plan to use it as a parking spot for short-term goal funding. (4) Avoid funds with unusually high yields relative to their stated category — yield outliers in the MMF world almost always reflect either reduced credit quality, longer-than-average maturities, or temporary fee waivers that will expire. The CFA Institute publishes extensive curriculum and research material on cash management and fixed-income analysis that retail investors can consult for deeper background. The most important rule: never accept yield without first understanding what the fund holds and what category it belongs to.[22, 23]