An S&P 500 fund looks like extreme diversification. What if it actually behaves like only 48 holdings?

📊 Increasing concentration, J.P. Morgan: A clear-eyed read on riding the benchmark.

🧭 Check your own spread: Your real diversification by company, sector and geography.

🔍 Taking a different approach: 41 stocks that beat the index without mirroring it.

An S&P 500 fund is sold as the safe, diversified, set-and-forget choice, and for most people it's a perfectly sensible core holding. But here's the thing. The index is weighted by size, so the biggest companies count for far more than the smallest. Seven giants now make up about a third of the whole pie, while the bottom few hundred barely move the needle. Add it up and your 500-stock fund carries the real concentration of roughly 48 equally-weighted stocks.

This doesn’t mean an index is bad. Concentration is only a problem when it's a surprise. If you know a third of your investment sits in seven tech names and you're happy with that, that's okay. The risk is holding that exposure unwittingly, unable to mentally prepare for what could be ahead. So the move is simply to check. Add up how much of your whole portfolio is really the same few stocks. 

When is more diversification too much?