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What Are Index Funds, and Why Are They So Popular?

The Stock Market for Beginners • Beginner Investing • 6 min

One of the most consequential ideas in the history of investing was, in hindsight, strikingly simple: instead of trying to pick the winning stocks, why not just buy a small piece of all of them? That's exactly what an index fund does — rather than a manager actively researching and selecting individual stocks hoping to beat the market, an index fund is built to track a specific market index (like the S&P 500) by holding all, or a representative sample, of that index's components in roughly the same proportions.

This approach is called "passive" management, as opposed to "active" management, where a fund manager makes ongoing decisions trying to outperform a benchmark index. Because passive management requires far less research, trading, and manager judgment, index funds typically charge much lower fees than actively managed funds — often a small fraction of a percent per year, compared to considerably higher fees common among actively managed funds.

Insider Angle: the index fund's popularity traces directly back to one person: John Bogle, who founded Vanguard in 1975 and launched what's now the Vanguard 500 Index Fund in 1976 — the first index fund available to individual investors. Bogle's core argument, backed by academic research, was that most professional active managers fail to beat their benchmark index over long periods once fees are accounted for — a finding that widely cited long-term studies, like S&P's own SPIVA reports, have continued to reinforce for decades since. That's the entire case for index investing in one sentence: if most experts can't reliably beat the market after fees, a low-cost fund that simply matches the market may actually be the better bet for most people.
Try This: Compare the expense ratio (annual fee) of a major S&P 500 index fund to the expense ratio of an actively managed U.S. stock fund. Calculate what that fee difference would cost, in dollars, on a $10,000 investment held for 20 years, assuming both funds returned the same amount before fees.
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