A money market fund is a type of mutual fund that invests in short-term, high-quality debt instruments — things like Treasury bills, government agency notes, and short-term corporate debt. The goal is simple: preserve your principal, stay highly liquid, and earn more than a traditional savings account. Money market funds are a popular place to park cash that you need to keep safe but want to put to work earning yield.
Money Market Fund vs. Money Market Account
These two products are easy to confuse but they are fundamentally different:
- Money market account (MMA): A bank deposit account, insured by the FDIC up to $250,000. Offered by banks and credit unions. Generally earns a slightly higher rate than a regular savings account. Your principal is guaranteed.
- Money market fund (MMF): An investment fund offered by a brokerage or fund company (Fidelity, Vanguard, Schwab). Not FDIC-insured. Regulated by the SEC. Your money is invested in short-term securities, not deposited in a bank. The risk of loss is extremely low but not zero.
In practice, most money market funds maintain a stable net asset value (NAV) of $1.00 per share. Only a handful of funds in history have ever “broken the buck” (fallen below $1.00), and government money market funds are considered extremely safe.
Types of Money Market Funds
- Government money market funds: Invest exclusively in U.S. government securities and repos collateralized by government securities. Considered the safest type. Examples: Fidelity Government Money Market Fund (SPAXX), Vanguard Federal Money Market Fund (VMFXX).
- Treasury money market funds: Invest only in direct Treasury bills, notes, and bonds. Interest may be exempt from state income taxes — an advantage for residents of high-tax states.
- Prime money market funds: Invest in a broader range of short-term corporate and bank debt in addition to government securities. Typically offer slightly higher yields but carry more credit risk and are subject to liquidity fees and redemption gates in certain market conditions.
How Much Do Money Market Funds Yield?
Money market fund yields move closely with the Federal Reserve’s benchmark interest rate. When the Fed raises rates, money market fund yields rise. When the Fed cuts rates, yields fall. In 2024–2025, with the Fed funds rate elevated, government money market funds were yielding 4–5.25%. As rates normalize, yields will moderate. Compare current yields at your brokerage against high-yield savings accounts to find the best spot for your cash.
When to Use a Money Market Fund
- Emergency fund storage: If your brokerage account is your primary financial hub, a money market fund lets you earn a competitive yield on your emergency fund while keeping it accessible and separate from your invested portfolio.
- Waiting for investment opportunities: Holding cash in a money market fund while waiting to deploy capital into the market earns yield rather than sitting idle.
- Short-term savings goals (1–2 years): For money you will need within 1–2 years, money market funds provide safety and yield without the risk of stock or bond market fluctuations.
- Brokerage cash sweep accounts: Many brokerages automatically sweep uninvested cash into a default money market fund. Check whether your brokerage’s default sweep account is competitive or whether you should manually move cash to a higher-yielding fund.
Tax Considerations
Interest earned in a money market fund is generally taxable as ordinary income in the year earned. Treasury money market funds may provide a state tax exemption on the portion of income derived from direct Treasury obligations. Check your fund’s year-end distributions and your state’s rules. Holding money market funds in a tax-advantaged account (IRA, 401(k)) avoids this issue entirely.
Is a Money Market Fund Safe?
Government money market funds have an exceptionally strong safety record. The main risks are:
- Breaking the buck: Historically rare. Government MMFs have never broken the buck. Prime funds broke the buck during the 2008 financial crisis at one fund.
- No FDIC insurance: Unlike bank accounts, MMFs are not federally insured. SIPC (which covers brokerage account insolvency) does not protect against investment losses in a fund.
- Yield risk: When interest rates fall, yields decline. The fund will not lose principal, but your income will drop.
Bottom Line
Money market funds are an excellent place for cash you need safe, accessible, and earning a return. For most brokerage users, a government money market fund offers a compelling combination of safety, liquidity, and yield — often matching or beating high-yield savings accounts. Check the yield on your brokerage’s default cash position and consider switching to a higher-yielding fund manually if your default is not competitive.