Wednesday, December 31, 2025

S&P 500 is a Market-Cap Weighted Index

It's that time of year, when pundits look back at the last 12 months and try to say something meaningful.

It's striking how the vast majority of those pundits say something like "2025 was a great year in the stock market; the S&P 500 is up 17 % this year".

Here's CNBC: S&P 500 slides, but gets set to close out 2025 with 17% gain; here's the BBC: US stock market ends 2025 on a high note after volatile year.

Deep down in the fine print, they'll mumble something about market-cap weighting and large cap stocks, of course.

It's really striking to see the details though, for this year has been very startlingly the year of winners and losers.

Let's just look at the top 10 holdings of the SP 500 in January and today, and see how they went. It's a simple table: where were they at the start of 2025, where are they now, and what was the year like for them?

So, if you owned the entire index this year, you indeed saw a 17% gain.

If you were a holder of just, say, Google or Broadcom or nVidia, you saw a 55% gain this year!

If you were a holder of Apple or Microsoft or Tesla or Berkshire Hathaway, you saw a gain of something from 7% to 17%.

But if you were a holder of Amazon or Meta, you actually saw a 2 or 3 percent loss this year.

Remember, these are very big companies. Amazon's market capitalization is 2.5 trillion dollars.

This year, there were winners and losers.

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