What is the difference between an ETF and an index mutual fund?

An index mutual fund and an index ETF can track the same benchmark (like the S&P 500), but the trading mechanics differ. ETFs trade on an exchange all day; mutual funds typically transact once per day at NAV.

ETFs can offer intraday flexibility and portability across brokers. Mutual funds can be easier for automatic investing and may support straightforward fractional investing depending on the platform.

If the exposure is identical, the best choice usually comes down to fees, taxes (in taxable accounts), and convenience for your investing habits. For long-term investing, behavior and consistency often matter more than tiny structural differences.