S&P 500 Concentration Risk: How Much Sits in the Top Ten?

The ten largest companies in the S&P 500 hold 39.4% of it by weight, measured from the SPDR S&P 500 ETF Trust's published holdings file as of August 10, 2026. Twenty-two companies hold half the index. That's the answer to the headline question, and it's the smaller half of what concentration data can tell you about the portfolio you actually own.

How concentrated is the S&P 500 right now?

Ten companies hold 39.4% of the index, and the top three alone hold 20.3%. These are the ten largest, with each company's weight summed across every share class the index lists. Figures computed by PortLens from State Street's published SPY holdings file, holdings as of August 10, 2026, using the arithmetic documented in our methodology.

#	Company	Ticker	Weight
1	NVIDIA	NVDA	7.90%
2	Apple	AAPL	6.79%
3	Alphabet	GOOGL / GOOG	5.66%
4	Microsoft	MSFT	5.64%
5	Amazon	AMZN	4.08%
6	Broadcom	AVGO	3.00%
7	Meta Platforms	META	1.96%
8	Eli Lilly	LLY	1.46%
9	Micron Technology	MU	1.46%
10	Berkshire Hathaway	BRK.B	1.45%
	Total		39.39%

The file lists 504 lines for 501 companies. Three companies appear twice because they have two listed share classes — Alphabet, Fox and News Corp — and only Alphabet is large enough for the difference to matter.

Why do published top-ten figures disagree?

Because "top ten" has two definitions and one date, and most published figures state neither. Count Alphabet's two lines separately and the top ten comes to 37.9%, because two of the ten slots go to one company and Berkshire Hathaway is pushed out of the list. Count Alphabet once and it's 39.4%. Both are correct; they answer different questions.

The date matters at least as much. Vanguard's published constituent file for VOO — with equivalent files for VXUS, VUG, VB, VIG and VGT at the same URL after swapping the ticker — puts the top ten at 36.4% on the line-counting definition with holdings as of June 30, 2026. State Street's file six weeks later puts the same measure at 37.9%. Nothing was restated. The index moved.

That's why every figure in this article carries a source and an as-of date, and why a concentration number quoted without one isn't checkable. A PortLens scan sums each ticker across every fund and direct position you hold, so a company reached through three funds is one line rather than three. It doesn't merge a company's separate share classes — it lists them the way the index does.

What does the index look like past the top ten?

It thins out fast. The chart below plots the cumulative share of the index as you add companies from largest to smallest.

Twenty-two companies hold half the index. One hundred hold 75.2%. The smallest 250 companies — half the membership — hold 8.5% between them, and only 84 of the 501 sit above the 0.20% each would carry if the index were equally weighted.

One number compresses all of that. Effective holdings — the inverse Herfindahl index, 1 / Σw², which weights each position by its size — says the S&P 500 behaves like 43.3 equally weighted companies. Not 500. That measure is the reason a position count is a poor description of a portfolio, and it's the same one PortLens runs on yours; what real diversification means covers why the count and the effective number come apart.

Is there a level of concentration that counts as too much?

No, and nobody can hand you one. There's no threshold in standard finance literature that says an index or a portfolio becomes unsafe at some weight, and PortLens doesn't publish one either.

What exists is a regulatory reference point, and it was written for funds rather than for people. Article 52(2) of the UCITS Directive lets Member States raise the ordinary 5% same-issuer limit to no more than 10%, subject to a separate 40% aggregate rule (accessed August 11, 2026). That rule governs UCITS funds, not personal portfolios, so it's a point of reference and not a limit that applies to you.

PortLens marks a scan for attention when one company reaches 10%, one sector reaches 40%, the top ten positions reach 60%, or effective holdings fall to 10 or fewer. The 10% figure borrows the UCITS reference point above; the other three are transparent, round-number design choices rather than regulatory limits or fitted optima. Crossing one changes visual emphasis and nothing else — it isn't a risk grade or a signal to trade. On those markers the index sits below the top-ten cutoff at 39.4%, and its 43.3 effective holdings are far above the effective-holdings one. All investing involves risk, including possible loss of principal, and past performance does not guarantee future results.

How much of your own portfolio is the index's top ten?

Less than the index in some mixes, more in others — which is the point of measuring rather than assuming. Below are three portfolios run through the same look-through arithmetic PortLens documents in our methodology, using Vanguard's published constituent files with holdings as of June 30, 2026, against the index's ten largest companies as of August 10, 2026. The two dates are six weeks apart, which is the same gap that moves the index figure by 1.5 points. "Its own top ten" counts share-class lines the way a scan does; "the index's ten largest" is the company-level list from the table above.

Portfolio	Companies owned	Effective holdings	Its own top ten	The index's ten largest
VOO alone	501	51.7	36.4%	37.5%
VOO 40% / VXUS 20% / VUG 15% / VB 15% / VIG 10%	3,626	107.7	25.0%	25.2%
VOO 50% / VUG 20% / VGT 20% / VXUS 10%	2,716	40.0	39.6%	39.7%

Four funds added around an S&P 500 holding cut the index's ten largest from 37.5% of the money to 25.2%, and took effective holdings from 51.7 to 107.7. Adding a growth fund and a technology fund instead moved both the other way: 39.7% and 40.0, from a portfolio holding 2,716 companies.

The routes are what a holdings list can't show. In the five-fund mix, NVIDIA is 4.89% of the portfolio and arrives through two funds; Apple is 4.80% and arrives through three, as 2.64% via VOO, 1.75% via VUG and 0.42% via VIG. Nobody bought VIG for Apple. The pairwise view is narrower and easier to check — VOO and VUG publish their shared holdings and weights — but a pair can't show a name arriving through three funds at once, which is the difference between ETF overlap and a whole-portfolio look-through.

What does the top-ten number not tell you?

It's a holdings measure, and its edges matter because the figure reads as more authoritative than it is.

• It says nothing about returns or correlation. Whether two positions move together is estimated from returns over a stated window; a weight is not an estimate of anything future.
• It's a snapshot. Every figure here carries its file's as-of date because index weights drift daily and reconstitutions move them in steps.
• This article doesn't plot a history, and that's a data limit rather than an editorial choice: a time series needs a run of dated holdings files, and PortLens stores the current one per fund.
• Portfolio figures are bounded by constituent coverage. PortLens covers the top ~50 holdings per ETF from our data provider plus curated mappings for major funds, and reports a coverage ratio on every scan. Below roughly 75% coverage the concentration figures understate your concentration rather than overstate it. The three portfolios above use full issuer files and come back at 100% coverage.
• International funds are the weak spot. Look-through is strongest for US large-cap funds; a fund that can't be resolved contributes nothing and shows up in the coverage ratio instead of your top ten.
• It doesn't know what you meant to build. A 39.6% top ten is a fact about a portfolio, not a verdict on it.

How do you measure concentration in your own portfolio?

Type your holdings in and read the look-through. A free PortLens scan computes effective holdings, the share of your money in your ten largest underlying companies, how many of your funds each of those companies arrives through, and the coverage ratio behind all three, with no account required to start.

Entry is manual. PortLens connects to no broker and has no CSV import, so each ticker and position size is typed by hand — a minute for five lines, longer for forty. A scan traces each weight to a published holdings file when one is available. If PortLens can resolve a fund only from its hand-maintained static mapping, the scan labels that fund's data approximate. Read the coverage ratio before the concentration figures, and look at the fund count beside each large company: a name arriving through three funds is one decision wearing three costumes.

Key takeaways

• The S&P 500's ten largest companies hold 39.4% of it counting each company once, or 37.9% counting listed share-class lines separately, from State Street's published SPY holdings file with holdings as of August 10, 2026.
• Twenty-two companies hold half the index, and the smallest 250 hold 8.5% between them — the index behaves like 43.3 equally weighted companies rather than 500.
• A concentration figure without a definition and an as-of date can't be checked. The same index measured six weeks earlier from a different fund's file reads 36.4% on the line-counting definition.
• Owning funds around an S&P 500 position moves your exposure to those ten names in either direction: 25.2% for one five-fund mix, 39.7% for a growth-tilted one, against 37.5% for the S&P 500 fund alone.
• No threshold in standard finance literature says how much is too much. The UCITS Directive's 5%-to-10% same-issuer limit is a reference point written for funds, and PortLens's own markers are design choices that change visual emphasis only.

This article is for information and education only and is not investment advice. Analytics referenced are computed as described in our methodology; see our disclosures.