Index Funds vs ETFs: Key Differences for US Investors

For most long-term investors, low-cost index investing is one of the simplest and most effective strategies there is. Instead of trying to pick winning stocks, you buy a fund that holds every company in a market index, such as the S&P 500 or the total US stock market, and you get that market's return, minus a small fee. Both index mutual funds and exchange-traded funds (ETFs) can do this. The differences between them are mostly about how you buy and hold them. This guide compares index funds vs ETFs so you can decide which is right for you.

Why index investing works

Most actively managed funds, which try to beat the market, fail to do so over long periods once their higher fees are taken into account. Index funds accept the market's return but charge very little, so more of the return stays with you. They also spread your money across hundreds or thousands of companies, reducing the risk that one company's problems hurt you badly.

How index funds and ETFs trade

An index mutual fund is bought and sold directly with the fund company, once a day, at the price calculated after the market closes. You can usually invest exact dollar amounts, which makes automatic monthly investing easy. An ETF trades on a stock exchange like a share, so its price changes throughout the day and you buy it through a brokerage account. Many brokers now offer fractional shares, which removes much of the old advantage mutual funds had for small, regular investments.

Minimums and costs

Some index mutual funds require a minimum first investment, while ETFs can be bought for the price of a single share, or less with fractional shares. Both types can be extremely cheap: the most popular broad-market funds charge expense ratios of a few hundredths of a percent a year. That matters, because fees compound against you over decades. Check the expense ratio, and whether your broker charges commissions or transaction fees for a particular fund.

To see how much fees matter, compare a fund charging 0.05% a year with one charging 1%. On a $100,000 portfolio, the first costs $50 a year and the second $1,000, and the gap grows as the portfolio grows.

Taxes in taxable accounts

In an ordinary taxable brokerage account, ETFs are generally more tax-efficient than mutual funds, because of the way new shares are created and redeemed. They tend to pass on fewer capital gains distributions, which you would otherwise owe tax on each year. Inside a tax-advantaged account, such as a 401(k) or IRA, that difference does not matter, since you are not taxed on gains year by year.

How to choose between an index fund and an ETF

If your 401(k) offers a low-cost index mutual fund, it is usually a fine choice: you are limited to the plan's menu anyway. In an IRA or brokerage account, choose based on convenience. If you like setting up automatic investments in round dollar amounts, a mutual fund may suit you; if you want low minimums and the best tax efficiency in a taxable account, an ETF often wins.

What matters far more than the wrapper is keeping costs low, staying diversified and investing consistently. See the 401(k) and IRA limits to make the most of tax-advantaged accounts first, and compare Roth and traditional accounts.

Building a simple index portfolio

Many investors use just two or three funds: a total US stock market fund, an international stock fund and a bond fund. The mix depends on how long you will invest and how much risk you can stomach; younger investors often hold more stocks, while those near retirement hold more bonds. Rebalancing once a year keeps the mix on target. Keep money you will need soon, such as an emergency fund, out of the stock market; see our guide to high-yield savings.

Frequently asked questions

Are ETFs better than index funds?

Neither is always better; ETFs are often more tax-efficient in taxable accounts, while mutual funds make automatic dollar investing easy.

Index funds vs ETFs: which is right for you?