Index Funds vs ETFs: What’s the Difference and Which Should You Buy?
Index mutual funds and ETFs can hold the exact same stocks, but they trade, cost and get taxed differently. Here is a clear comparison and how to choose.
"Buy an index fund" is some of the most common investing advice there is. Then you open a brokerage account and see both index mutual funds and ETFs tracking the same index. They are more alike than different, but the differences in trading, minimums and taxes can matter.
First, what is an index fund?
An index fund is any fund that tries to match the performance of a market index, such as the S&P 500 or the total U.S. stock market, by holding the stocks (or bonds) in that index. Instead of paying managers to pick winners, you simply own the market. That keeps costs low, and broad index funds have historically outperformed most actively managed funds over long periods once fees are included.
"Index fund" describes a strategy. "ETF" and "mutual fund" describe the wrapper the fund comes in. So an ETF can be an index fund, and many of the most popular ETFs are.
Index mutual funds vs ETFs at a glance
| Index mutual fund | Index ETF | |
|---|---|---|
| How you buy | Directly from the fund company or a brokerage | On a stock exchange, like a stock |
| Pricing | Once a day, at the closing price (NAV) | All day, at the market price |
| Minimum investment | Some funds require $1,000–$3,000 to start; others have none | Price of one share, or less with fractional shares |
| Automatic investing | Easy: set a fixed dollar amount | Depends on the brokerage supporting fractional or recurring ETF buys |
| Expense ratios | Can be very low for major index funds | Often very low |
| Tax efficiency (taxable accounts) | Good | Usually better |
The key differences explained
1. Trading and pricing
ETFs trade throughout the day, so the price changes minute to minute. Mutual fund orders are filled once per day at the net asset value (NAV) calculated after the market closes. For long-term investors, this difference rarely matters, and if anything, a once-a-day price discourages overtrading.
2. Minimums and automation
Mutual funds are easy to automate with exact dollar amounts, like "$200 every month." ETFs used to require buying whole shares, but many brokerages now offer fractional shares and recurring ETF purchases, which closes most of the gap.
3. Taxes
In a taxable brokerage account, ETFs are usually more tax-efficient. Because of the way ETF shares are created and redeemed "in kind," ETFs rarely have to sell holdings and distribute capital gains to shareholders. Mutual funds sometimes do, which can create a tax bill even if you didn't sell anything.
In tax-advantaged accounts like a Roth IRA or 401(k), this difference doesn't matter.
4. Costs
The most important number is the expense ratio, the annual fee as a percentage of your investment. Both formats offer broad index funds with very low fees. Also check for trading commissions (most major brokerages charge $0 for ETFs), transaction fees on mutual funds from other companies, and the bid-ask spread on thinly traded ETFs.
Why fees matter so much
Suppose two funds track the same index, one charging 0.05% a year and another 0.75%. On a $50,000 balance, that is $25 versus $375 a year. Over decades, as your balance grows, the gap can compound into tens of thousands of dollars. Since both funds own the same stocks, the cheaper one should almost always come out ahead.
Which should you choose?
- Investing in a 401(k): use what your plan offers, often index mutual funds or target-date funds.
- Investing in an IRA: either works. Choose whichever your brokerage makes easiest to automate at low cost.
- Investing in a taxable account: ETFs often have the edge on taxes.
- Investing small amounts automatically: mutual funds with no minimum, or ETFs at a brokerage with fractional shares.
Popular index types to know
- S&P 500: about 500 large U.S. companies. See what is the S&P 500.
- Total U.S. stock market: large, mid and small companies, often several thousand stocks.
- Total international: companies outside the U.S., for global diversification.
- Total bond market: a broad mix of investment-grade U.S. bonds to reduce volatility.
Many investors build a simple portfolio from just two or three of these, adjusting the stock/bond mix to their age and risk tolerance.
Key takeaways
- "Index fund" is a strategy; ETF and mutual fund are wrappers. Both can hold the same index.
- ETFs trade all day and are usually more tax-efficient in taxable accounts.
- Mutual funds are easy to automate with exact dollar amounts.
- The expense ratio matters more than the wrapper. Keep costs low.
Free download
Free 50/30/20 Budget Spreadsheet
Enter your take-home pay and expenses, and it splits your money into needs, wants and savings automatically.
- Works in Excel, Google Sheets and Numbers
- Built-in targets and "left to assign" tracker
- Plus short, practical money tips by email
We write practical, fact-checked guides on money and markets for U.S. readers. How we research and fact-check.
