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S&P 500 Concentration: How Much of the Index Is in 10 Stocks

Top 10 names now over 38% of the S&P 500. What that means for SPY holders, passive flows and tail risk.

S&P 500 concentration is the highest in recorded index history. The top 10 stocks account for over 38% of the index — more than the 1999 peak and roughly double the 1990s average. For passive investors holding SPY, VOO or IVV, this means roughly $0.40 of every dollar is exposed to the same 10 names, dominated by mega-cap technology.

This hub tracks the narratives that touch concentration: AI capex cycles, mega-cap earnings, the breadth divergence (cap-weighted vs equal-weighted SPX), and the tail risk that comes when a single name like NVDA drives both the index and the volatility regime. Cross-references explain why ROIC, panic selling and option Greeks matter when concentration shifts.

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Frequently asked

What percentage of the S&P 500 is in the top 10 stocks?

As of 2026, the top 10 names represent over 38% of the S&P 500 market cap. NVDA, MSFT, AAPL, GOOGL, AMZN, META and TSLA dominate the list. The historical average is around 20%; the prior peak was 27% in 2000.

Why does concentration matter for SPY investors?

A passive SPY holder has roughly 38 cents of every dollar in 10 names. Single-stock risk that was theoretical in a diversified index is now meaningful. A 20% drawdown in NVDA alone would drag SPY down by about 1.4% mechanically.

What is the equal-weighted S&P (RSP) and how does it compare?

RSP weights every S&P 500 name equally (0.2% each, rebalanced quarterly). When breadth is wide, RSP outperforms SPY; when concentration is rising, SPY outperforms. The RSP vs SPY ratio is a clean breadth indicator.

What has historically happened after concentration peaked?

1999-2000 peak: SPY underperformed RSP by 15+ percentage points over the next 3 years as concentration unwound. 2024-2026 levels are still in regime; reversal could trigger a similar mean-reversion trade if mega-cap earnings stumble.