Index fund vs. ETF: what's the difference?

An index fund is a strategy — track a benchmark like the S&P 500 rather than try to beat it. An ETF is a wrapper — a fund that trades on an exchange all day, like a stock. Many index funds are ETFs, but the two terms describe different things.

How do index funds and ETFs actually differ?

A traditional index mutual fund is priced once per day, after the market closes, at its net asset value (NAV). An ETF trades continuously during market hours at whatever price buyers and sellers agree on right then, the same as a single stock — you can watch the price move tick by tick and place a limit order at a specific price.

Is an ETF better than a mutual fund index fund?

Neither is unconditionally better. ETFs typically have no minimum investment beyond one share's price and trade instantly; mutual funds sometimes carry a minimum initial investment but let you buy an exact dollar amount rather than whole shares only. Expense ratios — the annual fee as a percentage of assets — matter most over decades, and the lowest-cost options tracking the same benchmark are often within a hundredth of a percentage point of each other.

Why this matters before you pick individual stocks

Both structures exist to solve the same problem: most individual stock-pickers, including professionals, don't consistently beat a broad index over long periods, so buying the whole index at minimal cost is a strong, boring default. Deciding whether to hold index funds/ETFs alongside or instead of individual-stock picks is a diversification and risk decision, not a verdict on any single ticker's forecast — see diversification for how spreading capital across holdings reduces single-stock risk.

Frequently asked questions

Is every ETF an index fund?

No — most ETFs track an index, but some are actively managed, meaning a manager picks holdings rather than mirroring a benchmark.

Is every index fund an ETF?

No — some index funds are structured as traditional mutual funds priced once per day, not as exchange-traded securities.

Which has lower fees, an index fund or an ETF?

It depends on the specific fund, not the wrapper type — the lowest-cost index mutual funds and index ETFs tracking the same benchmark are often within a hundredth of a percentage point of each other.