As you probably know, the S&P 500 is not calculated by adding up the closing prices of the 500 component stocks and dividing by 500. Instead, it is weighted based on market cap. This, the company with the largest market cap of $4 trillion, NVDA, would be about 40 times more impactful to the value of the S&P 500 compared to, say, DoorDash, with about a $100 billion market cap.
If the 500 components all moved up and down the same degree, the equal-weighted S&P would be in lockstep with the “normal” market-cap-weighted S&P, and for many years that was pretty much the case. In recent years, however, the standard S&P has been outpacing the equal-weighted one to an increasing degree.





