You Own an Index Fund Because It's "Diversified." Ten Stocks Now Make Up ~40% of It. Here's the Concentration Myth — and the Fix.
The whole point of an S&P 500 index fund was to spread your money across 500 companies. But the top 10 holdings now account for roughly 40% of the index — a record — and the Magnificent Seven alone are about a third of it. If a few AI mega-caps stumble, your "diversified" 401(k) goes with them. Here's what the concentration really looks like and the practical levers to de-risk without abandoning indexing.