What an Index Fund Does
An index fund is a type of mutual fund or ETF designed to match the performance of a specific market index. An index is just a predefined list of investments that represents a section of the market. For example, the S&P 500 index tracks 500 of the largest publicly traded companies in the United States. An S&P 500 index fund holds the same 500 companies in roughly the same proportions, so its performance closely mirrors the index itself.
Index funds are sometimes called "passively managed" because there is no fund manager actively picking which stocks to buy or sell. The fund simply follows the index. This is different from "actively managed" funds, where a manager makes decisions about what to hold, aiming to outperform the market.
Why Fees Matter More Than Most People Realize
One of the main reasons index funds get discussed so frequently is cost. Because they do not require a team of analysts making trading decisions, they tend to have much lower expense ratios than actively managed funds. The difference might sound small -- 0.03% versus 0.75%, for example -- but over decades, it compounds.
Consider this: on a $10,000 investment earning 7% annually over 30 years, a 0.03% expense ratio results in roughly $74,000 in total. The same investment with a 0.75% expense ratio results in roughly $57,000. That 0.72% difference in fees cost about $17,000 over the life of the investment. This is not an argument for or against any particular fund -- it is just the math of how fees work over time.
What the Research Shows
Multiple independent studies, including those published by S&P Dow Jones Indices (SPIVA reports), have consistently found that the majority of actively managed funds underperform their benchmark index over long periods of time, after accounting for fees. This does not mean active management never works -- some funds do outperform. But identifying which ones will outperform in advance has proven to be extremely difficult, even for professional investors.
This body of research is a significant reason why index-based investing has grown in popularity over the past two decades. It is also why index funds are commonly found in 401(k) plan lineups and are frequently referenced in financial education materials.
This content is for general educational purposes only and does not constitute investment advice or a recommendation to buy or sell any security. All investments carry risk, including the potential loss of principal. Past performance does not guarantee future results. Consider consulting with a qualified financial professional before making investment decisions.