S&P 500’s 15 largest stocks now hold a record 46.7% of the index

The S&P 500’s 15 largest stocks now account for a record 46.7% of its total market value. That matters because the S&P 500 is the default holding for retirement accounts, index funds and anyone told to “just buy the market.” Increasingly, buying the market means buying a small cluster of tech giants. Who’s carrying the index The concentration figure is approximately 46.7% as of mid-to-late October 2026, according to the research findings. Technology sector exposure across the index sits close to 46%. The top 10 stocks contribute around 40.1% of the index on their own. As of October 20, 2026, the heaviest hitters by market cap looked like this: NVIDIA: about $5.22 trillion to $5.24 trillionApple: about $4.96 trillion to $5.00 trillionAlphabet: about $4.11 trillion to $4.19 trillionMicrosoft: about $3.95 trillionAmazon: about $2.83 trillion to $2.84 trillion The combined weight of the three largest stocks exceeded 21% in October 2026. The previous record for the top three was 13.4%, set back in the mid-1980s. NVIDIA’s outsized role in the rally NVIDIA contributed about 13% of the S&P 500’s rally from March 30 to early October 2026. Its weight in the index reached roughly ...