Short answer: There are 2,536 index funds in the U.S., according to the Form N-CEN reports funds filed with the SEC (2025 Q3 to 2026 Q2). That’s about a fifth of the 11,887 funds that aren’t money market funds, but they hold roughly half of the money, and Vanguard, BlackRock and Fidelity together manage about 81% of index fund assets.
Ask how many index funds exist in the United States and you’ll usually get a vague answer: “thousands,” or a number from an industry report that counts things slightly differently from the next one. So we went to the source.
Every registered fund in the U.S. has to file an annual report with the Securities and Exchange Commission called Form N-CEN. One of its questions is simple: is this fund an index fund? We read the answers from every N-CEN filed over a full year and counted.
The short version: 2,536 index funds, run by well over 100 different fund managers, holding more than $16 trillion in average net assets. They make up only about one in five funds, but roughly half of the money. And a handful of companies run most of it.
If you’re new to the idea of an index fund, our plain-English guide explains the basics. This article is about the numbers.
How we counted
Form N-CEN is a census-style report that every registered investment company files once a year, covering things like who manages the fund, whether it’s an ETF, and whether it tracks an index. The SEC publishes the answers as downloadable data sets every quarter.
Because funds have different fiscal years, each quarter’s data set only contains the reports filed during that quarter. To get every fund once, we combined four quarters (the third quarter of 2025 through the second quarter of 2026) and kept each fund’s most recent report. When a fund had more than one report in the period (for example, a late amendment to an older year), we kept the one covering the most recent fiscal year. That gave us reports for fiscal years ending between March 2025 and April 2026.
A few ground rules, explained in full on our Editorial Methodology page:
- A fund counts as an index fund if it says so in its N-CEN. We didn’t second-guess the answers.
- We count funds, not share classes. A fund with five share classes counts once. (For the fee differences between share classes, see our S&P 500 fee analysis.)
- We left out 30 funds whose only filing in the period covered a fiscal year before 2025, so funds that may have closed don’t inflate the count.
- Money market funds are excluded from the comparisons below. None of them is an index fund, and their cash-like assets would distort the picture.
That leaves 12,188 funds in total, of which 11,887 are not money market funds.
The headline numbers
| Number of funds | |
|---|---|
| All funds (excluding money market funds) | 11,887 |
| Index funds | 2,536 |
| Index funds that are ETFs (or have an ETF share class) | 1,900 |
| Index funds with no ETF share class | 636 |
| All ETFs | 4,034 |
A note on the ETF line: a few fund companies, most notably Vanguard, run a single fund with both mutual fund share classes and an ETF share class. The N-CEN answers the ETF question for the fund as a whole, so those funds show up as ETFs in this table even though they also sell regular mutual fund shares.
Index funds are a fifth of the funds but about half of the money
Index funds make up about 21% of the non-money-market funds in our count. By assets, the picture flips.
N-CEN asks each fund for its average net assets over the reporting year. Added up, index funds report about $16.4 trillion. To compare that with the rest of the industry fairly, we also set aside funds that mostly invest in other funds (funds of funds) and feeder funds that invest through a master fund, since both would count the same money twice. On that basis, index funds hold about 50% of the assets of all long-term funds in our count.
That lines up well with the fund industry’s own figures. The Investment Company Institute (ICI), the industry’s trade group, reports that index mutual funds and index ETFs together held $19.1 trillion at year-end 2025, or 52% of long-term fund assets (ICI 2026 Fact Book). Our total is lower for three reasons:
- Timing. Our figures are averages over fiscal years that mostly end during 2025, while ICI’s are a snapshot taken at the end of 2025.
- Some big ETFs aren’t in N-CEN’s fund-level data. A few of the oldest and largest ETFs, including the SPDR S&P 500 ETF Trust (SPY), are legally unit investment trusts. They file N-CEN in a different format, so they aren’t in the fund-by-fund answers we counted.
- Definitions. ICI’s figures are built from its own survey data and categories, not from the funds’ N-CEN answers.
Put simply: two different methods, the same conclusion. Roughly half of the money in U.S. long-term funds now sits in index funds, even though most funds are still actively managed.
Most new ETFs aren’t index funds anymore
The word “ETF” is often used as if it meant “index fund.” That’s no longer a safe assumption.
Of the 4,034 ETFs in our count, 1,900 (47%) say they’re index funds and 2,134 (53%) say they aren’t. By number, actively managed and other non-index ETFs now outnumber index ETFs.
The trend is even clearer among new funds. N-CEN asks whether a filing is the fund’s first one, which is a good sign that the fund launched recently. Of the 912 ETFs filing their first N-CEN in our period, 760 (83%) are not index funds.
The money is a different story. Non-index ETFs in our count report just under $1 trillion in average net assets, a small fraction of what index ETFs hold. Most new ETFs are active, but most ETF money is still in index funds. If you’re buying an ETF because you want a low-cost index fund, check the prospectus: the fund’s objective will say whether it tracks an index. Our comparison of index mutual funds and ETFs explains the rest of the differences.
Index mutual funds: fewer, but bigger on average
The 636 index funds with no ETF share class are the traditional index mutual funds. They’re outnumbered almost three to one by index ETFs, but they’re far from a niche: together they report about $3.8 trillion in average net assets.
They also tend to be bigger. The median index mutual fund reports about $620 million, against about $259 million for the median index ETF. The largest include the Fidelity 500 Index Fund ($684 billion), the Vanguard Total Bond Market II Index Fund ($325 billion), the Vanguard Institutional Index Fund ($320 billion) and the Schwab S&P 500 Index Fund ($115 billion). Several of the biggest index mutual funds are used mainly by retirement plans and other institutions, which is one reason they stay large even as ETFs attract most of the new launches.
Who runs them: a very concentrated business
Index investing is often described as a crowded market. By number of funds, it is. By money, it’s dominated by three companies.
We matched each index fund to the investment adviser named in its N-CEN and grouped the advisers by fund family:
| Fund family | Index funds | Share of index fund assets |
|---|---|---|
| Vanguard | 101 | 48.8% |
| BlackRock (iShares) | 427 | 21.5% |
| Fidelity | 114 | 10.2% |
| State Street (SPDR) | 133 | 4.8% |
| Schwab | 48 | 3.9% |
| Invesco | 204 | 1.9% |
A few things stand out:
- Vanguard runs about half of all index fund money with just 101 funds. Its funds are few but enormous.
- BlackRock has by far the most index funds (427), mostly iShares ETFs covering almost every corner of the market.
- Vanguard, BlackRock and Fidelity together hold about 81% of index fund assets in our count.
- State Street’s share would be larger if SPY were included. Its flagship ETF is a unit investment trust and isn’t in these fund-level answers.
Big funds, and a long tail of small ones
The ten largest index funds in our count hold about 41% of all index fund assets. The biggest ones will be familiar:
| Fund | Average net assets reported |
|---|---|
| Vanguard Morningstar Total Stock Market Index Fund (formerly Vanguard Total Stock Market Index Fund) | $1.90 trillion |
| Vanguard 500 Index Fund | $1.41 trillion |
| Fidelity 500 Index Fund | $684 billion |
| iShares Core S&P 500 ETF | $677 billion |
| Vanguard Total International Stock Index Fund | $486 billion |
These are fund-wide figures, so for the Vanguard funds they include every share class, from the ETF shares to the Admiral and institutional mutual fund shares.
At the other end, the median index fund reports average net assets of about $309 million, and 889 index funds (35%) report less than $100 million. Small funds aren’t necessarily bad, but they’re more likely to close or merge, and they often can’t match the fees of the giants.
Not every index fund is a plain index fund
“Index fund” covers more than broad, buy-and-hold funds. The N-CEN answers show some of the variety:
- 314 index funds say they seek a multiple or the inverse of an index’s return. These are leveraged and inverse funds, such as funds that aim for twice or minus the daily return of an index. Together they report about $105 billion in average net assets. They’re designed around daily returns, so over longer periods their results can be very different from a simple multiple of the index.
- 302 index funds track an index created by an affiliate of the fund’s own company, sometimes called self-indexing.
- 399 index funds track an index that’s only available to that fund (the N-CEN calls these exclusive indexes). Many are custom or rules-based “smart beta” indexes rather than broad market benchmarks.
- 73 index funds are funds of funds, which build their portfolio from other funds.
None of this is a problem in itself. But it means “it’s an index fund” tells you less than it used to. The index a fund follows, and what it charges to follow it, still matter.
How to tell whether a fund is an index fund
You don’t need the SEC’s data sets to check a single fund. Three quick places to look:
- The fund’s name. Many include “Index,” but not all: plenty of index ETFs don’t, and a few funds with “Index” in the name use custom rules rather than a broad benchmark.
- The investment objective. It’s the first thing in every summary prospectus. An index fund will say it “seeks to track” or “seeks investment results that correspond to” a named index. If the objective talks about “long-term capital appreciation” with no index named, it’s probably actively managed.
- The index itself. If a fund does track an index, look up what that index is. “S&P 500” or “total U.S. stock market” is one thing; an index built by the fund’s own company, or one that resets its exposure every day, is another.
What this count can’t tell you
A census like this has limits worth being upfront about:
- It relies on the funds’ own answers. We didn’t reclassify any fund. A fund that tracks an index but answered “no,” or the reverse, is counted the way it answered.
- It’s a moving picture. Funds launch, merge and close every week. Our count reflects each fund’s latest annual report in a one-year window, not a single day.
- It leaves out products that aren’t registered funds, such as some commodity and currency ETFs, and the unit investment trusts mentioned above.
- It says nothing about quality. Being an index fund doesn’t make a fund cheap or well run. That’s what the fee comparisons elsewhere on this site are for.
What the numbers mean for you
A few practical takeaways:
- Choice isn’t the problem. With more than 2,500 index funds, there’s an index fund for almost any slice of the market. The challenge is picking one that fits and doesn’t overcharge.
- “ETF” doesn’t mean “index fund.” More than half of ETFs, and most new ones, aren’t index funds. Read the objective in the prospectus.
- “Index fund” doesn’t mean “simple.” Leveraged, inverse and custom-index funds all count as index funds.
- Size and cost tend to go together. The largest funds are also among the cheapest. In our analysis of S&P 500 index fund fees, the lowest-cost options for individual investors came from the biggest fund families.
Common questions
Are all ETFs index funds? No. Of the 4,034 ETFs in our count, 1,900 (47%) report that they’re index funds. Among ETFs filing their first N-CEN report in our period, 83% were not index funds. Most ETF money is still in index funds, though, so check the fund’s objective in its prospectus before you buy.
Which companies run the most index fund money? Vanguard, with about 48.8% of index fund assets in our count, followed by BlackRock (iShares) with 21.5% and Fidelity with 10.2%. Together they hold about 81%. BlackRock runs the most index funds by number: 427, mostly iShares ETFs.
Why do other sources give a different number? Because they count different things: share classes instead of funds, only ETFs, or with leveraged and inverse funds included or left out. Our count uses each fund’s own answer to the index fund question on Form N-CEN, and our Editorial Methodology explains the method.
The bottom line
By the SEC’s own filings, there are more than 2,500 index funds in the U.S., around a fifth of all funds, and they hold roughly half of the money in long-term funds. Three companies run most of that money, while hundreds of smaller funds, and a fast-growing wave of active ETFs, fill in the rest.
This article is general information based on public filings, not personal advice. See our Financial Disclaimer.
Sources and data notes
- SEC, Form N-CEN data sets, 2025 Q3 to 2026 Q2: index fund, ETF, money market, fund of funds, master-feeder, leveraged/inverse, affiliated and exclusive index answers; first-filing indicator; average net assets; investment adviser names. Each fund’s most recent report in the period, covering fiscal years ending March 2025 to April 2026. Funds are counted by SEC series ID.
- Investment Company Institute, 2026 Investment Company Fact Book, Chapter 2: index mutual fund and index ETF assets ($19.1 trillion) and share of long-term fund assets (52%) at year-end 2025.
- Asset figures are averages reported by each fund for its own fiscal year, not a single-date snapshot, and fund-family totals group advisers by name. All counts and shares are our own calculations from SEC data.
Data as of the 2026 Q2 SEC data sets. Sources checked on September 29, 2026.