Money Market Funds: How They Work and When to Use Them
Types of Money Market Funds
| Type | What It Holds | Yield | Tax Treatment | Risk Level |
|---|---|---|---|---|
| Government | Treasury bills, agency debt, repos | Moderate | Federal tax; may be state-exempt | Lowest |
| Treasury-Only | Only US Treasuries and repos backed by Treasuries | Slightly lower | State tax-exempt | Lowest |
| Prime | Commercial paper, CDs, corporate debt | Higher | Fully taxable | Low (slightly more credit risk) |
| Municipal (Tax-Exempt) | Municipal short-term debt | Lower nominal, higher after-tax | Federal-exempt; may be state-exempt | Low |
Money Market Funds vs. Savings Accounts
| Factor | Money Market Funds | High-Yield Savings Accounts |
|---|---|---|
| Yield | Typically 0.10–0.50% higher | Competitive but slightly lower |
| FDIC Insurance | No — not FDIC insured | Yes — up to $250,000 |
| Access | Same-day or T+1 settlement | Instant transfers |
| Minimum | Often $1–$3,000 | Usually $0 |
| State Tax | Government/Treasury funds may be exempt | Fully taxable |
| Provider | Brokerage account (Fidelity, Vanguard, Schwab) | Banks (online or traditional) |
When Money Market Funds Make Sense
Emergency fund parking. If you keep your emergency fund in a brokerage account, a government money market fund offers competitive yield with near-instant access. It’s the functional equivalent of a savings account inside your investment account.
Cash allocation in a portfolio. When your asset allocation calls for 5–10% cash, a money market fund is the default choice. It earns a yield while you wait for deployment opportunities.
Short-term savings goals. Money you need within 1–12 months (tax payments, down payment, upcoming large purchase) should not be in stocks or bonds. Money market funds preserve capital while earning something.
Rising rate environments. Unlike bond ETFs, money market funds benefit immediately from rising rates because their holdings mature quickly and roll into higher-yielding instruments. When the Fed is hiking, money market yields ratchet up within weeks.
Risks and Limitations
Not FDIC insured. Money market funds are securities, not bank deposits. While government funds have never “broken the buck” (fallen below $1 NAV), one prime fund did in 2008 during the financial crisis. Post-crisis reforms have significantly reduced this risk.
Yield lags in falling-rate environments. When the Fed cuts rates, money market yields drop quickly — often faster than savings account rates. Your income can fall significantly in a rate-cutting cycle.
Inflation risk. Money market yields often trail inflation, meaning your purchasing power erodes slowly. They’re a place to park cash, not grow wealth.
Key Takeaways
- Money market funds invest in short-term, high-quality debt to preserve capital and provide liquidity with a competitive yield.
- Government and Treasury funds are the safest; prime funds offer slightly higher yields with marginally more credit risk.
- They’re not FDIC insured, but government money market funds have never broken the buck.
- Best used for emergency funds, cash allocation, and short-term savings — not long-term wealth building.
- In high-tax states, Treasury-only funds offer state tax exemption that can boost your after-tax return.
Frequently Asked Questions
What is a money market fund?
A money market fund is a mutual fund that invests in short-term, high-quality debt instruments like Treasury bills and commercial paper. It aims to maintain a stable $1.00 share price while paying a yield that tracks short-term interest rates.
Are money market funds safe?
Government and Treasury money market funds are considered very safe — they’ve never lost investor principal. Prime money market funds carry slightly more risk due to corporate debt holdings, though post-2008 reforms have added significant protections.
How are money market funds different from money market accounts?
A money market fund is a mutual fund held in a brokerage account — not FDIC insured. A money market account is a bank deposit product — FDIC insured up to $250,000. They serve similar purposes but have different risk profiles.
What yield can I expect from a money market fund?
Money market yields closely track the federal funds rate. When the Fed’s target rate is 5%, money market funds typically yield 4.8–5.2%. When rates are near zero, yields fall to 0.01–0.10%.
Can I lose money in a money market fund?
It’s extremely rare but technically possible. One prime money market fund “broke the buck” in 2008. However, regulatory reforms since then have made this scenario much less likely, especially for government funds.