Index Fund Statistics (2026)

The index fund has gone from a fringe idea to the center of gravity in American investing. US index mutual funds and ETFs held about $16.2 trillion at the end of 2024, with index mutual funds alone at $6.9 trillion across 513 funds (see the table below).

Together they now make up 51% of all long-term fund assets, a majority, and the vast majority of ETF money (over 90%) is index-based rather than actively managed.

The rise has been rapid and steady. Index funds held just 19% of long-term fund assets in 2010, climbing to 28% in 2015, 40% in 2020, and crossing the symbolic 50% line in 2024 (see the chart and table below).

In effect, more than half of every dollar in US funds is now indexed, a complete reversal of the active-dominated landscape of a generation ago.

2024 marked a genuine milestone: passively managed US funds ended the year at $13.29 trillion, edging past the $13.23 trillion in actively managed funds, the first time passive assets exceeded active.

It is the culmination of a two-decade shift. Active domestic-equity mutual funds have seen net outflows every year since 2005, while index funds and ETFs have taken share continuously.

Cost is the index fund's decisive edge. Index equity mutual funds averaged an asset-weighted expense ratio of just 0.05% in 2024, versus 0.59% for actively managed funds, more than a tenfold difference (see the chart and table below).

That gap compounds relentlessly. On a $100,000 portfolio, the difference between 0.05% and 0.59% is about $540 a year, every year, before accounting for the returns those fees would have earned.

The fee advantage translates directly into better results. According to SPIVA, 65% of active large-cap funds trailed the S&P 500 in 2024, and the failure rate rises with time: 84% over 10 years and 89.5% over 15 (see the chart and table below).

The verdict is damning at the long horizons that matter for investors: over the 15 years ending 2024, not one of 22 US equity fund categories had a majority of active managers beat their benchmark. Costs, and the zero-sum nature of active management, make the index very hard to beat.

Investors have voted with their money. From 2015 to 2024, index domestic-equity funds and ETFs took in about $2.9 trillion of net new cash, while active domestic-equity mutual funds bled about $3.0 trillion (see the table below).

The flows also concentrate in the cheapest funds: money pours disproportionately into the lowest-cost quartile, and VOO alone drew $137.7 billion in 2025. The market is not just choosing index funds, it is choosing the cheapest ones.

The league tables now sit atop index funds. Vanguard's VOO became the first ETF ever to cross $1 trillion in June 2026, dethroning SPY, while VTSAX became the first mutual fund near $2 trillion (see the table below).

The four largest S&P 500 or total-market vehicles, VOO, VTSAX, IVV, and FXAIX, are all index funds. A single, cheap, broad index fund is where the most money in the world has chosen to sit.

Index funds are now a structural part of the stock market. At the end of 2024, index domestic-equity funds held about 18% of the entire US stock market's value, more than the 12% held by active domestic-equity funds.

The other 70% is held by everyone else, pensions, hedge funds, insurers, and individuals holding stocks directly. But among pooled funds, indexing is now the dominant force.

It began as a flop. John Bogle launched the first retail index fund, the First Index Investment Trust (now the Vanguard 500 Index Fund), on August 31, 1976. It aimed to raise $150 million and pulled in just $11 million, prompting critics to call it "Bogle's Folly."

The idea, that most investors are better off matching the market cheaply than trying to beat it, proved prophetic. The fund has returned about 11.44% a year over its life; $10,000 invested at launch grew to nearly $2 million by 2026.

Index funds are now mainstream household holdings. About 48% of US mutual-fund-owning households owned at least one index equity mutual fund in 2024, a share that has climbed as index options filled 401(k) menus and advisor models.

That penetration, plus the continued shift of retirement money into target-date and index products, is a big part of why the passive share keeps rising even in years when active funds outperform.

Within indexing, the story is relentless cost compression. About 87% of index equity mutual fund assets sit in the lowest-cost quartile of funds, versus 73% for active equity funds, meaning index investors cluster in the very cheapest options.

Scale reinforces it: the average index equity mutual fund holds $13.6 billion versus $2.5 billion for the average active fund, and larger funds can charge less. The result is a virtuous cycle of lower fees attracting more assets attracting lower fees.

The data points to a simple default. For most investors, a low-cost, broad index fund is the highest-probability path to good long-term returns, because it captures the market's return at minimal cost, and the market is very hard to beat.

This is the same lesson that shows up in the SPIVA scorecards and the investor behavior gap: costs and timing mistakes are what separate investors from the market's return, and a cheap index fund minimizes both. It is not glamorous, but the evidence for it is about as strong as evidence gets in investing.