What is Index Fund?

An index fund is a mutual fund or exchange-traded fund (ETF) constructed to match or track the components of a financial market index, such as the S&P 500 or the Russell 2000. Unlike actively managed funds, where professional portfolio managers constantly buy and sell individual securities to try to beat the market, an index fund employs a passive investment strategy. The fund manager's objective is simply to mirror the performance of the target index by holding the same assets in identical proportions.

This passive approach eliminates the need for expensive research teams and active trading, which translates to substantially lower expense ratios for investors. Because index funds trade securities only when the benchmark index itself changes, they generate very low portfolio turnover. This not only keeps transaction costs down but also minimizes taxable capital gains distributions, making index funds highly tax-efficient for investors holding them in taxable accounts.

Over multi-decade horizons, data from the SEC and academic research show that low-cost index funds consistently outperform the vast majority of active mutual funds after fees are factored in. By providing instant, broad market diversification, index funds allow individual investors to capture long-term market returns while avoiding the high risks and fees associated with active stock-picking.