Money market funds have relatively low risks, compared to other mutual funds (and most other investments). By law, they can invest in only certain high-quality, short-term investments issued by the U.S. government, U.S. corporations, and state and local governments. Money market funds try to keep their net asset value (NAV) — which represents the value of one share in a fund — at a stable $1.00 per share. But the NAV may fall below $1.00 if the fund's investments perform poorly. Investor losses have been rare, but they are possible.

Money market funds pay dividends that generally reflect short-term interest rates, and historically the returns for money market funds have been lower than for either bond or stock funds. That's why "inflation risk" — the risk that inflation will outpace and erode investment returns over time — can be a potential concern for investors in money market funds.