The usual reason to add a growth fund to an S&P 500 fund is to tilt: more of the companies that are compounding fastest, less of the rest. The filings say the tilt is real but the diversification is not — and one number makes the point better than any argument.
Only 3.55% of VUG sits in companies IVV does not already own. The other 96.45% is a reweighting of stocks you have.
Data as of 2026-06-30 (filing period) · received by the SEC 2026-08-25 (IVV) and 2026-08-28 (VUG) · analysis written 2026-09-26. Both file again for the September quarter in late November.
What each fund holds
| IVV | VUG | |
|---|---|---|
| Net assets | $889.6bn | $379.5bn |
| Stocks held | 507 | 151 |
| Behaves like | 51.5 equal holdings | 19.8 equal holdings |
| Ten largest | 36.4% of the fund | 60.4% of the fund |
VUG holds under a third as many stocks as IVV and behaves like two fifths as many. Its ten largest positions are three fifths of the fund; IVV's are just over a third. How the effective-holdings figure is computed.
The overlap, and what it is made of
119 companies appear in both funds, carrying 56.9% of the combined weight. The largest are the same names, weighted roughly half again as heavily in VUG:
| Shared holding | Weight in IVV | Weight in VUG |
|---|---|---|
| NVIDIA | 7.51% | 12.62% |
| Apple | 6.59% | 11.66% |
| Microsoft | 4.29% | 7.61% |
| Alphabet (both classes) | 5.84% | 10.28% |
| Amazon | 3.62% | 4.47% |
| Broadcom | 2.77% | 4.28% |
| Meta Platforms | 1.92% | 3.41% |
| Tesla | 1.84% | 3.27% |
| Eli Lilly | 1.47% | 2.81% |
Held together the two behave like 31.0 equal holdings — well below IVV's 51.5 on its own. Buying both does not widen the portfolio; it moves weight from the bottom four hundred of the S&P 500 into the top ten, which both funds already hold.
What each holds alone
Only in IVV — 42.76% of it. The value and cyclical half of the index: Micron 2.02%, Berkshire Hathaway 1.42%, JPMorgan Chase 1.36%, Johnson & Johnson 0.95%, Exxon Mobil 0.88%, and roughly 380 smaller names. This is the part VUG is designed to leave out, and it is the part that makes IVV behave like 51.5 holdings rather than 20.
Only in VUG — 3.55% of it. Seagate 0.61%, SpaceX 0.29%, Snowflake 0.25%, Bloom Energy 0.24%, Cloudflare 0.23%. Growth companies outside the S&P 500, including one large private holding. Genuinely additive exposure, and it is three and a half cents on the dollar.
That asymmetry — 42.76% against 3.55% — is the whole comparison in two numbers.
So what does adding VUG actually do?
It raises your weight in about nine companies you already own and lowers it in about four hundred. Whether that is worth doing is a judgement about those nine companies, not a diversification decision, and it should be made as such.
A portfolio of IVV alone behaves like 51.5 equal holdings. IVV plus VUG behaves like 31.0. If the reason for adding a second fund was to spread risk, the filings say it did the opposite. Test your own combination — the calculator reads through to positions and reports the combined figure.
The S&P 500 is half as spread out as it was in 2019
Everything above is one filing. The archive holds twenty-eight, and the more interesting number is not how the two funds differ today but what has happened to both:
| Filing period | IVV behaves like | IVV top ten | VUG behaves like | VUG top ten | |
|---|---|---|---|---|---|
| 2019-09-30 | 111.9 | 21.6% | 42.6 | 38.9% | |
| 2020-09-30 | 68.6 | 27.9% | 28.7 | 45.3% | |
| 2021-09-30 | 74.5 | 28.1% | 29.9 | 46.3% | |
| 2022-09-30 | 72.2 | 27.7% | 23.9 | 49.2% | |
| 2023-09-30 | 64.3 | 30.4% | 22.4 | 53.7% | |
| 2024-09-30 | 52.4 | 34.6% | 20.3 | 57.5% | |
| 2025-09-30 | 45.3 | 38.8% | 20.1 | 59.7% | |
| 2026-06-30 | 51.5 | 36.4% | 19.8 | 60.4% |
IVV held 507 stocks in 2019 and holds 507 now. The count did not move. The number that describes the portfolio fell from 111.9 to 51.5 — the S&P 500 today behaves like less than half the number of holdings it behaved like seven years ago, and its ten largest went from a fifth of the fund to well over a third.
VUG did the same from a more concentrated start: 42.6 to 19.8, top ten past 60%, while shedding 133 of its 284 names.
This is worth stating plainly because it changes what "the index" means. Someone who bought IVV in 2019 for broad exposure now owns something measurably narrower, without having done anything and without the fund changing its rule. Both funds hold what the market weights, and the market concentrated.
It also reframes the question the essay started with. If the reason to add a growth fund was to tilt toward the largest compounders, the S&P 500 has been doing that on its own the whole time — and the 2026 figure ticking back up, 45.3 to 51.5, is the first move the other way on record.
Returns, as the funds reported them
From Item B.5 of the filings themselves, not from a price feed:
| Whole series | Months | Last 12 months | Best month | Worst month | |
|---|---|---|---|---|---|
| IVV | +183.4% | 84 | +22.3% | +12.8% | −12.4% |
| VUG | +230.9% | 84 | +18.6% | +15.1% | −12.8% |
Over seven years VUG returned 231% against IVV's 183%; over the last twelve months on record it returned less, 18.6% against 22.3%. Both agree with an independently computed price series, so the figures are published rather than withheld — the funds where our two readings disagree are named here.
Neither fund lends much of itself: IVV has 0.17% out on loan across 21 named borrowers, VUG 0.24% across 22. Megacaps are easy to borrow elsewhere. The lending dataset.
Hold both, and this is the portfolio
Half in each, looked through to the companies rather than described fund by fund:
| Combined weight | Company |
|---|---|
| 10.1% | NVIDIA |
| 9.1% | Apple |
| 6.0% | Microsoft |
| 4.5% + 3.6% | Alphabet (two share classes) |
| 4.0% | Amazon |
| 3.5% | Broadcom |
| 2.7% | Meta Platforms |
76.8% of the money sits in the 118 companies both funds hold. Seven companies are 39% of it. The mix behaves like 31.0 equal holdings against 35.7 if you simply averaged the two funds' own figures — so combining them is worse than either the arithmetic or the brochure suggests.
Blending the two funds' own filed monthly returns over the 60 months both reported gives +87.2% for the pair, with a best month of +12.4% (April 2026) and a worst of −10.8% (April 2022). That is the mix as the funds themselves reported it, assuming these weights held throughout and rebalanced monthly — run your own.
What this does and does not tell you
- One date. 30 June 2026 holdings. Index funds move with their indices.
- Overlap is measured by weight. 119 shared names out of 507 and 151 sounds small; 56.9% of the money is the figure that matters.
- Past returns say nothing about future ones, and nothing here recommends either fund.
- The positions behind every number: point-in-time files, free under CC BY 4.0.