As the third quarter of 2025 ended, the market capitalization of the S&P 500 (Index: SPX) added up to $59.32 trillion.

Four weeks later, Slickcharts estimated the total market cap of the index adds up to $62.25 trillion.

Yesterday, the three biggest component stocks of the index, Nvidia (Nasdaq: NVDA), Microsoft (Nasdaq: MSFT), and Apple (Nasdaq: AAPL) had one of their best trading days. NVDA's stock flirted with reaching a $5 trillion valuation, while the stocks of both Microsoft and Apple both surpassed $4 trillion in market value during the trading day, only for AAPL shares to fall below the level by the close.

Together, these three stocks alone account for more than one-fifth of the total value of the S&P 500 index. The following chart gives an indication of how much of the index' total market cap is accounted for by these three $4+ trillion firms.
 

Going into the trading day of 29 October 2025, it looks likely that NVDA will soon become the world's first $5 trillion company. FXStreet estimates that will officially happen when NVDA's share price closes above $205.36.

Our own back-of-the-envelope math using Slickcharts' market cap data for the S&P 500 and NVDA's relative share of the index suggest the stock would have to close at or above $205.44 per share to reach that threshold, which is definitely in the same ballpark. Regardless of the actual stock price at which it happens, when combined with two other companies joining NVDA in the $4+ trillion valuation club, it's kind of the stock market equivalent of seeing a three-planet conjunction in the sky. It doesn't really mean anything, but it's cool to see happen for the first time ever all the same.

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