A mutual fund is an investment vehicle that pools money from many investors to purchase a diversified collection of securities — stocks, bonds, or both. When you buy shares in a mutual fund, you own a small piece of every investment in that fund’s portfolio.
Related: What Is a 1031 Exchange?
Mutual funds are one of the most common ways Americans invest, particularly through 401(k) plans. They offer instant diversification, professional management, and accessibility for investors of all sizes.
How Mutual Funds Work
A fund manager (or team of managers) selects and manages the investments inside the fund according to the fund’s stated objective. Investors buy shares of the fund at the net asset value (NAV), which is calculated once per day after the market closes. Unlike ETFs, you cannot trade mutual fund shares throughout the day.
Returns come from:
- Dividends or interest paid by the underlying securities (distributed to shareholders)
- Capital gains when the fund sells securities at a profit (also distributed)
- Growth in the fund’s NAV as its holdings increase in value
Types of Mutual Funds
Stock (Equity) Funds
Invest primarily in stocks. Sub-categories include large-cap, small-cap, growth, value, and international funds. Generally offer higher long-term returns with higher short-term volatility.
Bond (Fixed Income) Funds
Invest in government, municipal, or corporate bonds. Lower volatility than stock funds, lower long-term returns. Often used to balance portfolio risk.
Balanced / Allocation Funds
Hold both stocks and bonds in a fixed ratio (e.g., 60/40). A one-fund diversified portfolio option for moderate-risk investors.
Index Funds
Track a specific index (like the S&P 500) rather than actively selecting stocks. Lower fees, less manager dependency, historically strong performance against actively managed alternatives.
Target-Date Funds
Automatically adjust the stock-to-bond ratio as you approach a target retirement year. Popular in 401(k)s because they require zero maintenance — choose your retirement date, invest, and let the fund rebalance itself.
Active vs. Passive Mutual Funds
The fundamental debate in mutual fund investing:
- Actively managed funds: A manager makes decisions about what to buy and sell, attempting to beat the market. Higher fees (often 0.5% to 1.5% expense ratio). Research consistently shows most active managers underperform their benchmark index over 10+ years.
- Passively managed (index) funds: Track an index mechanically. Much lower fees (often 0.03% to 0.10%). Historically outperform the majority of active funds over long periods.
For most investors, low-cost index funds are the most evidence-backed choice.
Mutual Fund Costs
Fees matter more than most investors realize. The expense ratio is the annual percentage of your investment charged to cover fund operating costs. On a $100,000 investment:
- 0.03% expense ratio = $30/year
- 1.00% expense ratio = $1,000/year
Over 30 years, the difference between a 0.03% fund and a 1.00% fund on a $100,000 initial investment growing at 7% annually is roughly $150,000 in lost wealth.
Also watch for:
- Sales loads: Front-end (charged when you buy) or back-end (charged when you sell) commissions. Avoid load funds — no-load alternatives perform just as well or better.
- 12b-1 fees: Marketing and distribution fees embedded in the expense ratio. Look for funds with no 12b-1 fees.
- Transaction fees: Some brokerages charge a fee to buy certain mutual funds. Look for no-transaction-fee funds.
How to Buy a Mutual Fund
You can buy mutual funds through:
- Your 401(k) or 403(b): Most workplace retirement plans offer a menu of mutual funds
- An IRA at a brokerage: Fidelity, Vanguard, Schwab, and others offer access to thousands of funds
- A taxable brokerage account: For investing beyond retirement account limits
- Directly from the fund company: Vanguard, Fidelity, and T. Rowe Price allow you to open accounts directly with them
Minimum initial investment requirements vary. Some Vanguard funds require $3,000 initially; others have no minimum. Fidelity has $0 minimums on most of their index funds.
Mutual Fund vs. ETF
Both can track the same index, but ETFs trade throughout the day like stocks, while mutual funds price once daily. ETFs tend to have slightly lower expense ratios and better tax efficiency in taxable accounts. Mutual funds are more common in 401(k) plans and allow automatic investment of exact dollar amounts rather than whole shares.
For most retirement account investors, mutual funds work perfectly. For taxable brokerage accounts, ETFs may have a slight tax efficiency advantage.
The Bottom Line
Mutual funds are a simple, effective way to diversify your investments across hundreds or thousands of securities with a single purchase. Focus on low-cost index funds, avoid sales loads and high expense ratios, and hold long-term. For most people, a three-fund portfolio of a total US stock market fund, an international fund, and a bond fund covers everything you need.
Related: What Is an Expense Ratio? How Fund Fees Affect Your Returns in 2026