The Top 15 Stocks in the S&P 500 Are Now 47% of the Value. In 2000 Bubble, It Was 27%

On Oct. 21, 2026, the 15 largest S&P 500 stocks accounted for a record 46.7% of the index’s market value, leaving the other 485 companies with 53.3%. That was 19.5 percentage points above the 27.2% held by the 15 largest during the 2000 dot-com bubble. Nvidia made up 7.5%, Apple 7.1%, Alphabet 5.9% and Microsoft 5.6%; those four totaled 26.1%, and the next 11 added about 20.6%. The 434 smallest members roughly matched the five largest in value, a record gap. The S&P 500 weights companies by market value, so rising prices lift the largest firms’ share automatically.