A money market mutual fund pools your cash with other investors' money and puts it into short-term, low-risk debt
A money market mutual fund is a fund that invests in very short-term loans — usually bonds and notes that mature in less than a year. The fund buys these from governments, banks, and large corporations. When you buy shares in the fund, you own a piece of that pool. The fund pays you interest based on what it earns, minus its operating costs.
Money market funds are different from stock mutual funds because they hold debt instruments instead of company shares. They are also different from money market accounts at banks, which are deposit products insured by the FDIC. A money market mutual fund is a security — it is not insured by the government, though the debt it holds is usually very safe.
The main appeal is that money market funds offer higher interest rates than regular savings accounts while keeping your principal relatively stable. They are often used as a temporary holding place for cash you do not want to invest in stocks but do not want sitting idle in a checking account.
Key Takeaways
- Money market mutual funds invest in short-term debt like Treasury bills and commercial paper, not stocks.
- The interest you earn comes from the fund's holdings and is paid out to shareholders minus management fees.
- Your principal can fluctuate slightly because money market funds are not FDIC-insured, though the risk is typically very low.
- Money market funds are most useful for cash you need to keep liquid but want earning more than a savings account offers.
- The interest rate and fees vary by fund, so comparing options before you invest matters.
What money market funds actually hold
Money market funds buy short-term debt instruments that mature in 13 months or less. The most common holdings are U.S. Treasury bills (issued by the federal government), commercial paper (short-term loans from corporations), and certificates of deposit from banks. Some funds also hold municipal bonds or other government debt.
The fund manager decides which specific securities to buy based on the fund's stated strategy. Some money market funds focus on Treasury securities only, which are backed by the U.S. government. Others buy a mix that includes corporate debt, which typically pays a higher rate but carries slightly more risk. The fund's prospectus — the document you receive before investing — describes exactly what types of debt it holds.
Because these loans are short-term and issued by stable borrowers, the risk that you lose money is low. But it is not zero. If a corporation defaults on its commercial paper or a bank fails, the fund's value can drop slightly. This is why money market funds are not insured like bank deposits.
How the interest you earn gets calculated
The interest rate on a money market fund is called the yield. It changes daily based on what the fund's holdings are earning. When interest rates in the broader economy are high, money market fund yields are high. When rates fall, so do the yields.
The fund collects interest from all the debt it holds, then distributes that income to shareholders. You typically see this as a daily accrual — the fund adds a tiny amount to your account value each day. Some funds pay out the interest monthly or quarterly; others let it reinvest automatically.
The fund charges a management fee, called an expense ratio, which is subtracted from the interest before you receive it. Expense ratios for money market funds are usually between 0.1% and 0.5% per year, though some are lower. A fund earning 5% with a 0.2% expense ratio pays you roughly 4.8%. Always check the expense ratio before you invest, because it directly reduces what you earn.
Why your principal can move slightly
Money market funds aim to keep the share price stable at $1 per share. In practice, the value can drift up or down by a few cents. This happens because the market value of the debt the fund holds changes every day, even though the debt will mature soon.
If interest rates rise, the value of existing bonds falls (because new bonds now pay more). If interest rates fall, existing bonds become more valuable. The fund marks its holdings to market value daily, so your share price reflects these tiny shifts. Most of the time the movement is less than a penny, but it can happen.
This is why money market funds are not the same as a savings account. A savings account guarantees your principal. A money market fund does not. However, the risk is small enough that money market funds are considered very conservative investments.
Money market funds versus savings accounts and CDs
A savings account at a bank is FDIC-insured up to $250,000 and your principal never changes. The trade-off is that savings account rates are usually lower than money market fund yields. Right now, savings accounts typically pay 4% to 5%, while money market funds may pay 5% to 5.5%, depending on the fund and current rates.
A certificate of deposit (CD) locks your money up for a set period — three months, one year, five years — in exchange for a may provide rate. If you withdraw early, you pay a penalty. Money market funds have no lock-up period; you can withdraw your money any day the market is open.
A money market account at a bank is a hybrid. It is FDIC-insured like a savings account but often pays a higher rate. The catch is that many money market accounts limit how many withdrawals you can make per month. Money market mutual funds have no withdrawal limits.
| Product | FDIC Insured | Typical Rate | Withdrawal Limits | Principal may provide |
|---|---|---|---|---|
| Savings Account | Yes, up to $250k | 4% to 5% | None | Yes |
| Money Market Account | Yes, up to $250k | 4.5% to 5.5% | Often limited | Yes |
| Certificate of Deposit | Yes, up to $250k | 4% to 5.5% | Locked for term | Yes |
| Money Market Mutual Fund | No | 5% to 5.5% | None | No (but very stable) |
When to use a money market fund
Money market funds work best for cash you want to keep liquid and earning interest but do not need to invest in stocks. Common uses include holding an emergency fund, parking money while you decide where to invest it, or keeping a portion of your portfolio in very safe, stable assets.
If you need the money within the next few months and want more than a savings account pays, a money market fund can make sense. If you need absolute certainty that your principal will not change, a savings account or CD is safer. If you have money you will not touch for years, stocks or bonds are likely to earn more over time.
Money market funds also work for people who want to avoid the lock-up period of a CD or the withdrawal limits of a money market account. You can move money in and out without penalty, and the rate is usually competitive with bank products.
How to buy a money market mutual fund
You can buy money market mutual funds through a brokerage account at firms like Fidelity, Vanguard, Charles Schwab, or your bank's investment division. You open an account, link a bank account for deposits, and then choose which money market fund to buy. The process is the same as buying any mutual fund.
Different brokerages offer different money market funds. Some have their own in-house funds with lower fees; others offer a selection from multiple fund companies. Compare the expense ratio and current yield before you choose. A difference of 0.2% in the expense ratio might not sound like much, but on $10,000 it adds up to $20 per year.
Once you own shares, you can check your balance and current yield online. You can withdraw money by selling your shares, which usually settles in one to two business days. Some brokerages let you write checks against a money market fund, though this is less common now.
Frequently Asked Questions
Can I lose money in a money market mutual fund?
Losing money is possible but rare. If a borrower defaults on the debt the fund holds, the fund's value can drop. However, money market funds hold very short-term debt from stable borrowers, so defaults are uncommon. The bigger risk is that your share price drifts down slightly when interest rates rise, but this is usually just a few cents.
Is a money market fund the same as a money market account?
No. A money market account is a bank deposit product that is FDIC-insured and guarantees your principal. A money market mutual fund is a security that invests in short-term debt and is not insured. Money market accounts often have withdrawal limits; money market funds do not.
How often does the interest rate change on a money market fund?
The yield changes daily based on what the fund's holdings are earning and current market conditions. You will see the current yield listed on the fund's fact sheet, which updates regularly. The rate you earn depends on when you buy and what the fund is holding at that time.
Do I have to pay taxes on money market fund interest?
Yes. The interest you earn is taxable income in the year you receive it. If the fund holds municipal bonds, some of the interest may be tax-free, depending on your state and the bonds held. Your fund sends you a 1099 form each year showing how much taxable interest you earned.
What happens if interest rates fall?
When interest rates fall, the yield on money market funds falls too. Your fund will earn less interest going forward. However, if you already own the fund, the value of your existing shares may actually rise slightly because the debt the fund holds becomes more valuable. The net effect depends on when you buy and sell.