ETFs vs Index Funds: What's the Difference?

People use these terms interchangeably, but they're not the same thing. An index fund is a strategy — tracking a market index. An ETF is a structure — how the fund trades. You can have an index fund that's an ETF, a mutual fund that tracks an index, or an ETF that doesn't track an index at all. Here's what actually matters.

The Real Difference: How You Buy Them

Mutual funds (like VTSAX or FXAIX) trade once per day at market close. You put in a dollar amount and get whatever number of shares that buys. Most have minimum investments ($1,000-$3,000 to start). They're what most 401(k) plans use.

ETFs (like VTI or SCHB) trade throughout the day like stocks. You buy whole shares at whatever the current price is. No minimum investment beyond the price of one share. Fractional shares are available at most brokers now, eliminating even that barrier.

Which Is Better?

For most people, it barely matters. If you're investing through a 401(k), you'll use mutual funds because that's what's available. If you're investing in a taxable brokerage account, ETFs have a slight tax advantage — they generate fewer taxable events due to how they're structured. In a Roth IRA or traditional IRA, the tax difference is irrelevant.

The expense ratios are nearly identical for equivalent funds. VTI (ETF) charges 0.03%. VTSAX (mutual fund) charges 0.04%. That one-hundredth of a percent difference is meaningless on any realistic portfolio size.

When ETFs Win

Taxable brokerage accounts (tax efficiency). Starting with a small amount (no minimums). You want to set limit orders or buy at a specific price during the day.

When Mutual Funds Win

401(k) plans (usually the only option). Automatic investing on a schedule (dollar amount, not share count). You want to invest every dollar without worrying about share prices.