What a money market mutual fund actually is

A money market mutual fund is a fund that holds short-term debt — mostly government bonds, corporate IOUs due within months, and bank certificates of deposit. It pools money from many investors and buys these low-risk, quick-to-mature securities. The fund then distributes any interest earned back to you, usually monthly or quarterly.

Money market funds sit between a savings account and a stock mutual fund in terms of risk and return. They are far safer than equity funds because they hold debt that matures soon and rarely defaults. But they pay more interest than a regular savings account because the securities they hold pay more than banks do. The trade-off is that the interest rate changes with the market — you do not lock in a fixed return the way you do with a certificate of deposit.

These funds are not the same as money market accounts at banks. A money market account is a deposit product insured by the FDIC. A money market mutual fund is a securities investment with no deposit insurance, though the risk of losing money is very low because the underlying securities are short-term and stable.

Key Takeaways

  • Money market mutual funds hold short-term debt like Treasury bills and commercial paper, which mature within months and carry minimal default risk.
  • Interest rates on money market funds fluctuate with market conditions, so your return is not fixed like it is in a savings account or CD.
  • These funds are safer than stock mutual funds but offer higher yields than bank savings accounts, making them useful for cash you need to keep accessible.
  • The fund charges a small expense ratio — typically 0.2% to 0.5% per year — which is deducted from your returns before you receive them.
  • Money market mutual funds are not FDIC-insured, but the securities they hold are so stable that losses are extremely rare.

What money market funds actually hold

Money market funds buy three main types of short-term debt. Treasury bills are IOUs from the U.S. government, maturing in weeks or months and backed by the full faith of the federal government. Commercial paper is short-term debt issued by large corporations — essentially a company borrowing money for a few months to cover operating costs. Certificates of deposit and bank deposits are money parked at banks, insured by the FDIC up to the deposit insurance limit.

The fund manager decides the mix based on what is available and what interest rates are offering. If Treasury bills are paying 5% and commercial paper is paying 5.2%, the manager might buy more commercial paper to boost returns — but commercial paper carries slightly more risk because a corporation could theoretically fail to repay. The manager balances yield against safety.

All of these securities mature within 13 months, and most within 90 days. That short timeline is what makes money market funds stable. A security maturing in 30 days is far less likely to lose value than a 10-year bond, because there is little time for circumstances to change.

How interest rates and yields work in money market funds

The interest you earn from a money market fund comes from the interest paid by the securities the fund holds. If the fund holds Treasury bills paying 4.5% and commercial paper paying 5%, the fund's overall yield will be somewhere between those two rates, weighted by how much of each it owns. That blended yield is called the seven-day yield — the annualized return based on the past week's earnings.

The seven-day yield changes constantly because interest rates in the broader market change constantly. When the Federal Reserve raises its benchmark rate, new Treasury bills and commercial paper pay higher interest, so the fund's yield rises. When rates fall, new securities pay less, so the fund's yield falls. Your money does not move in and out of the fund — the fund simply reinvests the interest it collects into new securities at the new rates.

The fund also charges an expense ratio, a small annual fee (typically 0.2% to 0.5%) that comes out of the interest before you receive it. A fund with a 4.5% yield and a 0.3% expense ratio will pay you roughly 4.2%. Lower-cost funds, especially index funds that track a money market benchmark, charge closer to 0.1%.

Why someone might use a money market fund instead of a savings account

A money market mutual fund pays more interest than most savings accounts because the securities it holds pay more than banks do. In recent years, when interest rates have been higher, money market funds have paid 4% to 5% while savings accounts paid 3% to 4%. That difference compounds over time if you are holding cash for months or years.

Money market funds also work well for money you need to keep liquid — accessible within a day or two — but do not need to touch immediately. If you have an emergency fund, a down payment you are saving for, or cash from a bonus you have not yet decided what to do with, a money market fund lets that money earn more than it would sitting in a checking account.

The downside is that money market funds are not FDIC-insured. If the fund itself failed — an extremely rare event — you could lose money. A savings account is insured up to $250,000 per depositor per bank. For most people, the extra yield is worth the tiny additional risk, but it is a real difference to understand.

How to buy a money market mutual fund

You buy money market mutual funds through a brokerage account — the same place you would buy stocks or other mutual funds. Open an account with a brokerage like Fidelity, Vanguard, Charles Schwab, or your bank's investment arm. Search for money market funds in the fund screener, filter by expense ratio and current yield, and place an order.

Most brokerages offer several money market funds to choose from. Some track the entire money market (index funds), while others are actively managed and focus on specific types of securities. Index funds usually have lower expense ratios because they simply hold whatever is in the benchmark rather than paying a manager to pick securities.

Once you own shares, the interest accrues and is usually reinvested automatically — the fund buys more shares with the earnings. You can withdraw your money any time, though it may take a day or two to settle. Some brokerages let you write checks against a money market fund, making it function almost like a checking account with higher interest.

Money market funds versus other places to park cash

A high-yield savings account at an online bank currently pays similar rates to money market funds (3% to 5%, depending on the bank and the current rate environment) and is FDIC-insured. The main advantage of a savings account is the insurance; the main advantage of a money market fund is that some offer check-writing and slightly higher yields in certain rate environments. For most people, a high-yield savings account is simpler and safer.

A certificate of deposit locks in a fixed rate for a set term — six months, one year, five years. If rates are high and you do not need the money for a year, a CD is often better because you lock in that rate. But if rates are rising, a money market fund lets you benefit from the increases. CDs also penalize early withdrawal.

A Treasury bill bought directly from the U.S. government (through TreasuryDirect.gov) is safer than a money market fund because it is backed by the government itself, not a fund manager. But you have to buy in $100 increments, and your money is locked up until the bill matures. A money market fund gives you more flexibility and diversification across many securities.

Risks and limits of money market funds

Money market funds are very stable, but they are not risk-free. The main risk is that a security the fund holds could default — a corporation could fail to repay its commercial paper, for example. This is extremely rare because money market funds only buy from large, creditworthy borrowers. But it can happen, and if it does, the fund's value drops slightly and your return is reduced.

Another risk is interest rate risk, though it works in your favor most of the time. If you buy a money market fund when rates are 5% and rates then fall to 2%, your fund's yield will fall too. Your money is not locked in at 5%. This is not a loss — you still own the same number of shares — but your future earnings are lower. This is why money market funds are best for money you might need to use soon, not money you are trying to grow over years.

Money market funds also carry no FDIC insurance. A savings account is insured up to $250,000. If you are parking a very large sum, splitting it between multiple savings accounts at different banks might be safer than putting it all in one money market fund.

Frequently Asked Questions

Can I lose money in a money market mutual fund?

Losses are extremely rare because money market funds hold only short-term, stable securities. But yes, it is technically possible if a borrower defaults or if the fund manager makes poor decisions. You are not protected by FDIC insurance the way you are in a savings account. For most investors, the risk is negligible, but it exists.

How often do I get paid interest from a money market fund?

Interest accrues daily and is usually distributed monthly or quarterly, depending on the fund. Most brokerages automatically reinvest the distribution, buying more shares of the fund with the earnings. You can change this to receive the interest as cash if you prefer.

What is the difference between a money market fund and a money market account?

A money market account is a bank deposit product insured by the FDIC. A money market mutual fund is a securities investment with no deposit insurance. Money market accounts often have lower yields and may require higher minimum balances, but they are safer because they are insured.

Should I use a money market fund or a high-yield savings account?

Both currently offer similar interest rates. A savings account is simpler and FDIC-insured, making it the better choice for most people. A money market fund makes sense if you want check-writing features or if a specific fund has a notably higher yield. Compare the rates and insurance coverage before deciding.

Do I have to pay taxes on money market fund interest?

Yes. Interest from a money market fund is taxable income in the year you earn it, reported on a 1099-DIV form. If the fund holds Treasury securities, the interest is exempt from state and local taxes but not federal taxes. Tax-exempt money market funds exist for investors in high tax brackets, holding municipal bonds instead of Treasuries.