Money market funds are often used for brokerage cash, emergency reserves, or money awaiting investment. Their risk is usually lower than stock or bond funds, but principal is not guaranteed.
Key Takeaways
- Mutual fund, not bank account: Shares are securities rather than insured deposits.
- Short-term holdings: Portfolios emphasize highly liquid debt instruments and cash equivalents.
- Several fund types: Government, prime, and tax-exempt funds follow different portfolio rules.
- Yield follows short-term rates: Income can rise or fall as money-market interest rates change.
How a Money Market Fund Works
The fund pools investor assets and buys short-maturity instruments such as Treasury securities, government obligations, certificates, commercial paper, or municipal instruments depending on its category.
Dividends generally reflect income earned by the portfolio after fund expenses. When short-term rates fall, money market fund yields can fall quickly as older holdings mature and are replaced.
Government, Prime, and Tax-Exempt Funds
| Type | Typical focus |
|---|---|
| Government | Cash, U.S. government securities, and qualifying repurchase agreements |
| Prime | Short-term corporate and bank obligations in addition to other eligible instruments |
| Tax-exempt | Short-term municipal securities designed to generate federally tax-exempt income |
Risk, tax treatment, NAV structure, and liquidity provisions can differ by fund type and whether the fund serves retail or institutional investors.
NAV Structure and Breaking the Buck
Many retail and government money market funds seek to maintain a stable $1.00 NAV using permitted valuation rules. Institutional prime and institutional tax-exempt funds generally use floating NAVs that move with the market value of their assets.
What “Breaking the Buck” Means
If a stable-NAV money market fund’s value falls enough that it must reprice below $1.00, the fund is said to have broken the buck. Breaking the buck is rare, but it is possible when portfolio losses become substantial.
Market stress can also produce heavy redemptions and, for certain funds, liquidity fees under current money-market-fund rules.
Money Market Fund vs. Money Market Account
A money market account is a bank or credit-union deposit account. By contrast, a money market fund is an investment company regulated as a mutual fund.
Yield, Fees, and Tax Treatment
Money market fund yields generally move with short-term market rates. Expense ratios reduce what investors receive, and very low interest rates can make fees especially important.
Tax treatment depends on the fund’s holdings. Government or municipal funds can have different federal or state tax characteristics from prime funds.
Liquidity and Access to Cash
Many funds offer same-day or next-day redemption through a brokerage platform, but access is not identical to a checking account. Settlement practices, fund cutoffs, and extraordinary market conditions can affect timing.
Investors using a money market fund for emergency reserves should understand how quickly cash can move from the fund to a spendable account.
When a Money Market Fund Can Fit
Money market funds can fit short-term reserves, brokerage settlement cash, or portfolios seeking low-duration exposure. They are not substitutes for long-term growth investments and generally have lower expected returns than riskier assets over long periods.
Investors should compare yield, expense ratio, fund type, tax treatment, redemption mechanics, and whether principal stability or government backing of the underlying assets is important to the goal.