An index fund is a fund that simply buys and holds every stock in a market index — like the S&P 500 — to match the market's return at rock-bottom cost, no stock-picking required.
An index fund is a type of mutual fund or ETF that tracks a stock market index such as the S&P 500. Instead of paying a manager to pick winners, the fund mechanically holds the same stocks in the same proportions as the index, so your return closely matches the whole market's return.
This is passive investing. An active fund employs analysts who try to beat the market by choosing certain stocks — and charges high fees to do it. Decades of evidence show most active funds fail to beat their index after fees, which is why index funds have become the default for long-term investors.
An index fund's biggest edge is its tiny expense ratio — often under 0.10% a year versus 1% or more for active funds. That gap compounds: over decades, paying less in fees can leave you with tens of thousands of dollars more, even if the underlying market return is identical.
An index fund is a strategy; it can be wrapped as a traditional mutual fund (priced once a day) or as an ETF (trades all day like a stock). Both can track the same index. Pairing index funds with dollar-cost averaging is the classic hands-off plan.
See diversification in action: an index fund spreads risk across hundreds of stocks. Build a multi-stock portfolio yourself in the stock market simulator to feel how owning many names smooths the ride.
Not advice: educational content only. For authoritative basics see the SEC at investor.gov.
Related: what is a stock market index, what is an ETF, and how to diversify a portfolio.
An index fund is a fund that buys all the stocks in a market index, like the S&P 500, so its return matches the overall market at very low cost — no stock-picking needed.
For most long-term investors, yes. Most active funds fail to beat their index after fees, while index funds capture the market return with far lower costs.
An index fund is the passive strategy of tracking an index. It can be sold as a traditional mutual fund priced once a day, or as an ETF that trades all day like a stock.
Fees compound. An index fund charging 0.05% versus an active fund charging 1% can leave you with far more money over decades, even with the same underlying returns.