What We Pass Down

The chart above shows the S&P 500's own price level over whichever period you select — it does not, by itself, say whether that move was broad (most of the 500 companies participating) or narrow (driven by a handful of the largest names). Telling those apart requires a market-breadth series (like an advance/decline line) this site does not have a free, properly licensed feed for, so this panel does not claim to know which one you're looking at on any given day.

What is independently verifiable: the index's own top-10 weight has been a genuinely useful clue in the past. As of May 18, 2026, J.P. Morgan Asset Management calculated the top-10 S&P 500 companies at 40.8% of the index — a level the firm itself described as "well above the 26.6% tech bubble peak," and S&P Dow Jones Indices separately found no comparable concentration since mid-1965 (≈38%). When concentration sits that high, a move in the index is mechanically more likely to be driven by a small number of very large companies — not because of today's specific chart, but because of how index math works at that level of concentration.