Quick answer

Your fund may be more concentrated than its name suggests

An S&P 500 index fund holds about 500 companies, but it weights them by size, so the biggest ones carry most of the weight. Today about 40% sits in ten companies, many linked to AI. That is not good or bad by itself, but it means a fall in AI-related shares would affect a typical retirement account more than many people expect. You can check your own exposure using your fund's fact sheet.

How "a bit of everything" became "a lot of a few"

Most popular index funds are weighted by market value. When a company's shares rise, it automatically takes up more of the fund. As the largest tech companies grew, many of them on AI optimism, they came to dominate. S&P Dow Jones Indices says the top ten reached almost 40% of the S&P 500 in mid-2025, a level not seen since the mid-1960s.

Bar chart: the ten largest companies held 19 percent of the S&P 500 in 2015, 38.7 percent in October 2025, and almost 40 percent in mid-2025
The same chart as in our dot-com comparison: concentration has roughly doubled in a decade.

What that means for your money

Illustrative donut chart: 40 percent of a fund in 10 companies and 60 percent across the other 490
An illustration with round numbers. Your own fund may differ.

If AI-linked companies keep growing, concentrated funds benefit. If they fall together, the fund falls more than its "500 companies" label suggests. During the dot-com crash, funds heavy in tech fell much further than the wider economy did.

Not investment adviceThis article explains the debate; it is not investment advice and makes no prediction about prices. Whether concentration suits you depends on your goals, timeline and other savings.

How to check your exposure in ten minutes

  1. Find the fact sheet. Every fund publishes one on its provider's website, usually updated monthly or quarterly. Search the fund's name and "fact sheet".
  2. Read the top-ten holdings. Note the percentage for each, and add them up.
  3. Check your other funds. Target-date, technology and "global" funds often hold the same big names. List the overlaps side by side.
  4. Add individual shares. If you also own shares in any of those companies directly, count them too.
  5. Look at the total. Ask what share of your savings depends on the same handful of companies.

If the answer surprises you, the next step is a conversation with your pension provider or a licensed adviser, not a panic sale.

Terms worth knowing

  • Market-cap weighted: bigger companies make up a bigger share of the fund.
  • Equal-weight index: a version that gives each company the same share. S&P publishes one for the S&P 500.
  • Concentration: how much of a fund depends on its largest holdings.
  • Overlap: the same company appearing in several of your funds.
Do it in HigxelSee your savings next to your spending
  1. Add investment and pension accounts in Accounts with their current value.
  2. Update the balance when you get a statement.
  3. Watch your net worth change over time instead of daily prices.

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FAQ

Common questions

How much of the S&P 500 is in the top 10 stocks?

Almost 40% in mid-2025, according to S&P Dow Jones Indices. Another report put it at 38.7% in October 2025.

Is an S&P 500 fund still diversified?

It holds about 500 companies, but because it is weighted by size, a large share depends on a few of them.

Where can I see what my fund holds?

On the fund's fact sheet, published on the provider's website, which lists the top holdings and their weights.

About this article

Written with AI assistance by Higxel Editorial. Figures come from the sources listed; any example figures are labelled. This is general information, not financial or investment advice. Sources checked November 3, 2026. Some sources describe one country; local rules and costs differ.

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