"Is the S&P 500 too concentrated?" is asked constantly and almost always answered with one number about one index. The filings allow a better answer: take every fund that filed in 2019 and still files now, measure each one against itself, and see how widely the thing actually happened.
The answer is that it happened nearly everywhere in equities, that it happened hardest somewhere most people are not looking, and that one large category moved the other way entirely.
Measured from 640 funds with a filing in 2019 and at least twenty quarterly filings since · SEC Form N-PORT · written 2026-09-27 · re-measured as new filings arrive.
The measure, in one paragraph
A fund's holding count is not its diversification. A fund of 500 stocks where one is 8% behaves like far fewer than 500. Effective holdings — one divided by the sum of the squared weights — says how many equal holdings would produce the same spread. A fund with 500 names and an effective count of 51 is as concentrated as an equal-weighted portfolio of 51 stocks. Every figure below compares each fund's own earliest filing on record against its latest, so nothing depends on comparing one fund with another. Method and limits.
What happened, by category
| Funds | Median: now ÷ 2019 | Share that fell | Median top ten, 2019 | Median top ten, now | |
|---|---|---|---|---|---|
| Equity | 482 | 0.91 | 67% | 27.2% | 35.2% |
| Bond | 134 | 1.56 | 17% | 17.2% | 10.9% |
Two thirds of equity funds are measurably less spread out than they were, and the median one's ten largest positions have gone from roughly a quarter of the fund to more than a third.
Bond funds did the reverse, and not marginally: the median bond fund behaves like half again as many holdings as it did in 2019, and its top ten shrank from 17.2% to 10.9%.
That split matters because it rules out the easy explanation. If this were a measurement artefact — a change in how funds file, or in how this site reads them — it would show up in both categories. It shows up in one, in opposite directions.
It is worse in the large equity funds
Restrict to equity funds over $20 billion, the ones most people actually hold:
78 funds. 62 of them fell. Median ratio 0.76.
The typical large stock fund behaves like about three quarters of the holdings it behaved like in 2019.
| Fund | 2019 | Now | Ratio | Top ten then → now |
|---|---|---|---|---|
| VTI | 161.5 | 67.0 | 0.41 | 17.8% → 32.0% |
| VOO | 112.4 | 51.6 | 0.46 | 21.5% → 36.4% |
| IVV | 111.9 | 51.5 | 0.46 | 21.6% → 36.4% |
| VXUS | 550.4 | 280.1 | 0.51 | 8.4% → 12.4% |
| VUG | 42.6 | 19.8 | 0.46 | 38.9% → 60.4% |
| VEA | 414.5 | 268.9 | 0.65 | 9.2% → 13.2% |
| VTV | 97.6 | 97.0 | 0.99 | 22.8% → 23.6% |
| VGT | 15.1 | 15.1 | 1.00 | 56.0% → 59.4% |
The total US market fund and the S&P 500 funds have all roughly halved. Note the two that did not move: VTV, the value fund, is where it was; VGT, the technology fund, was already at 15 effective holdings in 2019 and had nowhere left to go.
The sharpest concentration is in emerging markets
This is the part that gets missed. Sorted by ratio, the equity funds over $10 billion that concentrated hardest:
| Fund | 2019 | Now | Ratio | Top ten then → now |
|---|---|---|---|---|
| DYNF | 175.2 | 34.1 | 0.19 | 15.9% → 43.6% |
| SCHA | 965.7 | 240.7 | 0.25 | 2.5% → 10.5% |
| VWO | 150.9 | 41.0 | 0.27 | 20.1% → 27.2% |
| SPEM | 149.7 | 41.1 | 0.27 | 18.7% → 26.3% |
| AVEM | 195.5 | 59.3 | 0.30 | 17.3% → 29.8% |
| EEM | 96.4 | 29.9 | 0.31 | 24.1% → 38.7% |
| IEMG | 121.1 | 38.9 | 0.32 | 21.5% → 33.9% |
| SCHE | 95.5 | 30.8 | 0.32 | 23.5% → 30.5% |
| GSLC | 146.9 | 50.6 | 0.34 | 17.8% → 36.2% |
| VT | 419.2 | 148.7 | 0.35 | 10.2% → 21.7% |
Five of the ten are emerging-market funds, and they are the largest ones: VWO, EEM, IEMG, SPEM, AVEM. The typical one lost about 70% of its effective holdings — a far sharper move than the S&P 500's 54%.
An emerging-market fund holds thousands of companies across dozens of countries and is bought precisely for breadth. VWO behaves like 41 equal holdings today, down from 151. It holds more than 6,000 stocks. Taiwan and Korea alone are now a quarter of some of these funds, and inside Taiwan one company does most of the work.
SCHA is the other surprise: a small-cap fund whose top ten went from 2.5% to 10.5% while its effective count fell from 966 to 241.
It did not happen steadily
A seven-year drift sounds like a slow grind. It was not. Taking each of the 482 equity funds' first filing in each year and indexing it to that fund's own 2019 reading, the median path is:
| Year | Median effective holdings vs its own 2019 | Change in the year |
|---|---|---|
| 2019 | 1.00 | — |
| 2020 | 0.97 | −3.1 pp |
| 2021 | 0.98 | +1.6 pp |
| 2022 | 0.98 | −0.0 pp |
| 2023 | 0.98 | −0.1 pp |
| 2024 | 0.96 | −2.7 pp |
| 2025 | 0.93 | −3.0 pp |
| 2026 | 0.93 | +0.3 pp |
Three years did nearly all of it — 2020, 2024 and 2025 — and the three years between them, 2021 to 2023, moved the median fund by a fifth of a point in total. Whatever this is, it arrives in bursts and then waits.
Two cautions on that table. It is a median across funds, so it understates badly: the large funds in the section above fell by a quarter to a half while the median fund fell 7%. And it uses each year's first filing, so a fund's position within the year is arbitrary — it shows shape, not precise timing.
The 2026 line is the first that has not fallen. One reading of a partial year is not a turn, and it will be re-measured when the next filings land.
Bond funds went the other way
| Fund | 2019 | Now | Ratio |
|---|---|---|---|
| TLH | 7.2 | 37.2 | ×5.17 |
| VMBS | 84.8 | 326.7 | ×3.85 |
| USIG | 1,999.4 | 6,893.6 | ×3.45 |
| IUSB | 177.2 | 604.4 | ×3.41 |
| IEI | 23.7 | 70.7 | ×2.98 |
| SHY | 31.4 | 83.2 | ×2.65 |
| BND | 656.9 | 877.7 | ×1.34 |
| AGG | 282.2 | 562.7 | ×1.99 |
A bond index grows when governments and companies issue more debt, and new issues enter at small weights. Seven years of heavy issuance leaves a bond fund holding more positions, each a smaller share. The two largest US bond funds, BND and AGG, both spread out.
So the same seven years concentrated stock funds and diluted bond funds. A 60/40 portfolio did both at once.
What this does not say
It does not say why. The filings record weights; they do not record the cause. A market-weighted fund holds more of what rose, so the mechanical reading is that a few large companies rose faster than the rest — but this data cannot separate that from index rule changes, and at least one fund on this site changed its cap mid-period with visible effect. Where a fund's own rule moved, that is in the number too, and the filings will not tell you which is which.
It does not say concentration is bad. Over the same seven years the more concentrated funds generally returned more, which is the uncomfortable half of this and is visible in the filed returns. A concentration figure describes a portfolio's shape, not its future.
It is not a complete census. 640 funds had a 2019 filing and twenty quarters since. Funds launched after 2019 cannot be in it, and funds that closed are not either — so this measures survivors, which is a known bias and pushes in an unknown direction.
Comparability is enforced, not assumed. Leveraged, inverse and heavily derivative funds are excluded; their notional would make the arithmetic meaningless. Securities-lending collateral is removed from every weight before anything is computed.
Check it yourself
Every figure here comes from one dataset and one method, both published:
- Effective holdings for every fund, quarter by quarter — the series behind the ratios
- The current snapshot for 1,087 funds
- The filings' own rows, if you would rather recompute than trust
- Your own portfolio, looked through
Free to reuse under CC BY 4.0. If you find an error, say so and it will be corrected in place with a dated note.