What a money market mutual fund is

A money market mutual fund is a fund that holds short-term debt instruments — mostly government bonds, corporate IOUs, and bank certificates of deposit that mature in less than a year. The fund pools money from many investors and buys these instruments in bulk, then distributes the interest earned back to you as dividends. The goal is stability and steady income, not growth.

Money market funds are often called "cash equivalents" because the underlying investments are so short-term and low-risk that the fund's value stays nearly flat. You are not betting on price movement the way you would with a stock fund. You are lending money to governments and corporations for a few months at a time and collecting the interest.

These funds sit between a savings account and a bond fund on the risk-and-return spectrum. A savings account is safer but pays almost nothing. A bond fund can fluctuate in value but pays more. A money market fund trades some safety for a slightly higher payout than savings, but stays much steadier than bonds.

Key Takeaways

  • Money market funds hold short-term debt that matures within a year, so the fund value stays stable and does not swing with market conditions.
  • The interest you earn comes from the fund's holdings — government bonds, corporate commercial paper, and bank CDs — and is paid to you as dividends.
  • Money market funds are not insured by the FDIC the way bank accounts are, so there is a small risk of loss if the fund's holdings default.
  • These funds work best as a temporary holding place for cash you need soon or as a low-risk portion of a longer-term portfolio.

How the fund earns and pays you money

The fund manager buys short-term debt instruments — say, a Treasury bill maturing in 90 days or a corporate note due in six months. The government or corporation pays interest on that debt. The fund collects all that interest from its many holdings and distributes it to shareholders as a dividend, usually monthly or quarterly.

Your return depends on what interest rates are doing. When the Federal Reserve raises rates, newly issued short-term debt pays more, so the fund's dividend goes up. When rates fall, new debt pays less, and your dividend shrinks. This is why money market fund yields move faster than bond fund yields — the underlying investments turn over so quickly that the fund's portfolio adjusts to new rates within weeks.

The fund also charges a small fee, called an expense ratio, which comes out of the returns before you see them. Money market funds typically have very low expense ratios — often 0.1% to 0.5% per year — because the holdings are simple and require little active management.

The difference between money market funds and money market accounts

A money market account is a bank product, not a mutual fund. It is a savings account with a higher interest rate, usually tied to money market rates, but it is FDIC-insured up to $250,000. The bank holds your money and pays you interest. You cannot lose your principal.

A money market mutual fund is not a bank product and is not FDIC-insured. The fund manager invests your money in debt securities. If those securities default — which is rare but possible — the fund's value can drop and you can lose money. However, money market funds have historically been extremely safe because they hold only the shortest, most creditworthy debt.

Money market accounts typically pay less interest than money market funds because the bank is taking on the insurance obligation. If you want the highest yield on cash you need to keep safe, a money market fund may pay more. If you want absolute protection and do not mind lower interest, a money market account at a bank is the right choice.

What types of debt money market funds hold

The fund manager can only buy debt that matures within a short window — usually 397 days or less. Within that constraint, the holdings fall into a few categories. Government money market funds hold U.S. Treasury bills and sometimes bonds issued by federal agencies. Prime money market funds hold corporate commercial paper (short-term corporate IOUs) and bank CDs. Municipal money market funds hold short-term debt issued by states and cities, often with tax advantages for residents of those states.

Most money market funds hold a mix of these instruments to spread risk. A fund might own Treasury bills, a few corporate notes from large stable companies, and some bank CDs. The manager constantly buys new debt as old debt matures, so the portfolio is always turning over.

The fund prospectus will tell you exactly what types of debt the fund holds and what percentage of the portfolio each type represents. If you want to know whether your fund is holding mostly government debt or mostly corporate debt, that information is public.

When money market funds make sense for your money

Money market funds work well as a temporary holding place for cash you will need within the next year or two. If you are saving for a down payment, a car, or a home repair, and you want the money to earn something while you wait, a money market fund beats a savings account. The yield is higher and the risk is minimal because the underlying debt is so short-term.

They also serve as the "cash" portion of a diversified portfolio. Many investors keep some money in stocks, some in bonds, and some in money market funds. The money market portion is stable and liquid — you can usually sell your shares and get the cash within a day or two — so it acts as a cushion if you need money in an emergency.

Money market funds are not meant for long-term growth. If you are investing for retirement or a goal 10 or 20 years away, you will not earn enough to keep pace with inflation. They are a short-term, low-risk tool, not a wealth-building vehicle.

The risks and limits of money market funds

The main risk is credit risk — the possibility that a corporation or bank whose debt the fund holds will default. This is rare, especially in prime money market funds that hold only the debt of large, stable companies. But it can happen. If a major corporation or bank fails, the fund's value drops and you lose money.

A second risk is interest rate risk, though it works differently in money market funds than in bond funds. If rates rise sharply, the fund's dividend will eventually rise too, but the fund's share price stays stable. You do not lose money, but you miss out on higher yields until the fund's holdings mature and the manager can reinvest at new rates.

Money market funds are also not FDIC-insured, so if the fund itself fails — an extremely rare event — you could lose money. The Securities Investor Protection Corporation (SIPC) covers mutual funds held at a brokerage, but only up to $500,000 per account, and only against brokerage failure, not fund failure.

Finally, money market funds have liquidity limits. During financial crises, some funds have temporarily restricted withdrawals to prevent a run on the fund. This is uncommon, but it has happened. If you need absolute certainty that you can access your cash instantly, a bank savings account is safer.

How to buy a money market mutual fund

You can buy money market funds through a brokerage account, a retirement account like an IRA, or directly from a mutual fund company. Most brokerages offer several money market funds to choose from, often with no transaction fee. You pick the fund, decide how much to invest, and the money is deployed within a day or two.

When you are choosing a fund, compare the expense ratio and the current yield. A lower expense ratio means more of the interest goes to you. The current yield tells you what the fund is paying right now, though that yield will change as interest rates move. You can find both numbers in the fund's prospectus or on the fund company's website.

Some money market funds have minimum investment amounts — often $1,000 or $2,500 — but many brokerages waive these minimums if you set up automatic deposits. Check the fund's details before you invest.

Frequently Asked Questions

Can I lose money in a money market mutual fund?

Yes, though it is rare. If the corporations or banks whose debt the fund holds default, the fund's value can drop. However, money market funds hold only the shortest, most creditworthy debt, so defaults are uncommon. During the 2008 financial crisis, one major money market fund "broke the buck" — its value fell below $1 per share — but this was an exception, not the rule.

How is a money market fund different from a money market account?

A money market account is a bank product that is FDIC-insured up to $250,000. A money market mutual fund is not insured and is not a bank product. Money market funds typically pay higher interest because they are not insured, but they carry a small risk of loss. Money market accounts are safer but pay less.

What happens to my money market fund when interest rates fall?

When rates fall, the fund's dividend shrinks because newly issued debt pays less interest. The fund's share price stays stable, so you do not lose money, but your income from the fund decreases. If you need higher income, you would have to move to a riskier investment like a bond fund.

Can I withdraw my money from a money market fund anytime?

Usually yes, within one or two business days. However, during severe financial stress, some funds have temporarily restricted withdrawals. This is rare, but it has happened. If you need absolute certainty that you can access cash instantly, a bank savings account is more reliable.

Are money market funds taxed differently than other mutual funds?

The interest you earn is taxed as ordinary income, just like interest from a savings account. If the fund holds municipal bonds, the interest may be tax-free at the federal level and sometimes at the state level, depending on where you live and where the bonds were issued. Check the fund prospectus to see what type of debt it holds.