Index fund vs ETF: what's the difference?

People throw around “index fund” and “ETF” like they mean the same thing — and sometimes they basically do. But there's a small, real difference. Here it is in plain words.

Both can hold a big basket of investments. The difference is mostly in how you buy and sell them, not what's inside.

Start with what they share

An index fund is any fund that just copies a whole market — say, all 500 big U.S. companies — instead of paying someone to pick winners. An ETF (exchange-traded fund) is a fund you can trade like a stock. Many ETFs are index funds. The two words describe different things. (See: what is an ETF.)

The real difference

• How you trade: an ETF trades all day at a live price, like a stock. A plain index mutual fund prices once a day, after the market closes.
• Minimums: mutual funds often want a set dollar amount. ETFs you can often buy by the share, sometimes a fraction of one.
• Taxes: in a regular account, ETFs are often a touch more tax-friendly. In a retirement account, this barely matters.

What actually matters more

For most people, the fee matters way more than the wrapper. A cheap index fund and a cheap index ETF that track the same market will perform almost identically. Chase the low fee, not the label. (See: expense ratios.)

So which do you pick?

Honestly? Either. Pick the cheap one your account offers and stop agonizing. Both spread your money across many companies, which is the whole point. (See: index funds: boring beats clever.)

The honest takeaway

“Index fund” describes what it owns; “ETF” describes how you trade it. They often overlap. Find the low-fee one, buy it, and don't lose sleep over the rest.