Two Ways to Own the Market

Index funds and Exchange-Traded Funds (ETFs) are both designed to track a market index — such as the S&P 500 — and both offer broad diversification at low cost. However, they have important structural differences that affect how you buy them, their tax efficiency, and their ideal use cases.

What Is an Index Fund?

An index fund is a type of mutual fund that passively tracks a market index. You buy shares directly from the fund company (like Vanguard or Fidelity) at the end-of-day net asset value (NAV) price. There is no intraday trading — you get the closing price regardless of when you place your order during the day.

Popular index funds include Vanguard's VTSAX (Total Stock Market Index), Fidelity's FZROX (Zero Total Market Index, with a 0% expense ratio), and Schwab's SWTSX.

What Is an ETF?

An ETF (Exchange-Traded Fund) is a fund that trades on a stock exchange throughout the day, just like a stock. You can buy and sell ETF shares at any time during market hours at the current market price. Most ETFs also track an index, making them functionally similar to index funds in terms of what they hold.

Popular ETFs include SPY (SPDR S&P 500 ETF), VOO (Vanguard S&P 500 ETF), and VTI (Vanguard Total Stock Market ETF).

Key Differences

  • Trading: ETFs trade intraday like stocks; index funds trade once per day at NAV.
  • Minimum investment: Index funds often have minimums ($1,000–$3,000); ETFs can be purchased for the price of one share (or fractionally for $1).
  • Tax efficiency: ETFs are generally more tax-efficient due to their unique creation/redemption mechanism, which avoids capital gains distributions.
  • Expense ratios: Both can be extremely cheap. Fidelity offers 0% expense ratio index funds. Vanguard's ETFs charge as little as 0.03%.
  • Automatic investing: Index funds support automatic monthly investments easily; ETFs require manual purchases or brokerage automation tools.

Which Should You Choose?

For most long-term investors, the choice is largely irrelevant — both will produce nearly identical returns. However, ETFs are generally better for taxable brokerage accounts due to their tax efficiency, and index funds are often more convenient for retirement accounts (401k, IRA) where you want to automate contributions without worrying about share prices.

The Bottom Line

Both index funds and ETFs are excellent investment vehicles. The most important decision is not which one to choose, but to start investing consistently. Use our Compound Interest Calculator to see how regular contributions grow over time regardless of the vehicle you choose.