Definition
A money market fund is a mutual fund investing in short-term instruments for cash management. Depending on its mandate, holdings can include government obligations, repurchase agreements, bank instruments, commercial paper, or municipal debt.
Some funds seek to keep a stable $1 share price. Institutional prime and institutional tax-exempt funds use a floating net asset value (NAV). Even a fund seeking a stable price can lose money. Money market fund shares are not FDIC-insured bank deposits.
Investor.gov's overview explains the distinction between stable and floating NAV funds.
Why It Matters
Cash management requires more than comparing the largest yield on a screen. The fund's holdings, expenses, redemption terms, and your broker's transfer process determine how it fits a near-term payment. A fund purchase is not necessarily an automatic cash sweep.
| Type | Main distinction |
|---|---|
| Government | At least 99.5% in cash, government securities, or fully collateralized repos |
| Prime | Can hold private-sector short-term debt, adding different credit exposures |
| Municipal or tax-exempt | Invests in municipal instruments; tax treatment needs checking |
Government and retail funds can seek a stable NAV. Institutional prime and institutional tax-exempt funds float. A government fund is not necessarily a Treasury-only fund, and a tax-exempt label does not establish exemption from every tax.
Reading the Yield and Redemption Terms
A seven-day yield annualizes a recent short period of net income. An effective yield also assumes compounding. Check which measure is displayed, its date, and whether fee waivers affect it. Neither promises what you will earn over the next year. Income changes as portfolio holdings mature and are replaced at different rates.
Liquidity fees can apply to certain funds. The SEC's 2023 reforms introduced mandatory fees for institutional prime and institutional tax-exempt funds under specified large redemptions, subject to exceptions, and permit discretionary fees for non-government funds. Do not rely on old descriptions of automatic gates tied to weekly liquidity thresholds. Read the current prospectus for the actual fund.
See the SEC's money market reform rule for the governing framework. Broker cutoffs, settlement, and bank-transfer availability still matter when planning a withdrawal.
Example
Suppose a hypothetical fund displays a 3.6% seven-day yield. Multiplying $10,000 by 3.6% gives $360, but that is only an annualized illustration. Your actual income depends on future rates, holding dates, expenses, and reinvestment. It is not a promised annual payment.
Before putting money needed for a bill into a fund, check:
- Whether its NAV is stable or floating and what instruments it holds.
- The yield date, expenses, and any temporary waivers.
- Whether your broker requires a sale before withdrawing cash.
- Redemption cutoffs, applicable fees, and bank-transfer timing.
Common Mistakes
- Confusing a fund with a deposit. A bank money market deposit account is a different product. Eligible deposits have FDIC coverage within applicable limits; fund shares do not.
- Treating a Treasury ETF as a stable-NAV mutual fund. ETFs trade at market prices with bid-ask spreads, and their prices can differ from NAV.
- Assuming all government-fund income is state-tax-exempt. Treasury, agency, and repo income can receive different treatment. Use the fund's annual tax supplement and state rules.
- Treating the current yield as fixed. A money market fund's income can rise or fall.
For deposit coverage, consult the FDIC's deposit insurance explanation. For ETF pricing and costs, see the SEC's fund fee guide.
FAQ
Can a money market fund lose money?
Yes. A stable $1 objective is not a guarantee, and some types use floating NAVs. Read the fund's credit, liquidity, and interest-rate risk disclosures.
Is a money market fund the same as SGOV or BIL?
No. Those are Treasury ETFs, with exchange trading and market-price fluctuations. Compare the product structure and access to cash as well as the displayed yield.
Is the seven-day yield comparable with a savings account APY?
Not directly without checking assumptions. A seven-day yield annualizes recent income; APY includes a compounding assumption. Neither comparison removes differences in insurance, rate changes, fees, or access to money.
Can I withdraw the same day?
It depends on the fund, broker, transaction time, and destination. Verify those terms before relying on a same-day withdrawal for a payment.
