A Stock Can Rise 5% and Barely Move the Index. Why?

The multiplication that matters

In a simplified market-cap-weighted calculation, contribution in percentage points is starting weight in percent × stock return in percent ÷ 100. A 0.10%-weight stock rising 5% contributes about +0.005 percentage points. A 6%-weight stock rising only 0.5% contributes about +0.030 percentage points—six times as much, despite the smaller stock move.

At a hypothetical starting index level of 5,000, those estimates correspond to about +0.25 and +1.50 index points respectively. Neither number is the stock's dollar price change.

A bigger ticker move is not always a bigger driver

Biggest Movers ranks visible securities by their own price movement. An Impact view asks how much they contribute under a weight reference. The two lists can be different because weight and return both matter. A stock with a large dollar price jump can also have a modest percentage return if its starting price was high.

Check the method and coverage

This shortcut is most natural for market-cap-based indexes over a consistent interval. The Dow is price-weighted, so its dollar price moves and divisor require a different calculation. If the displayed weights come from an ETF snapshot or only 30 selected securities, label that source and scope; the estimate is not the index provider's official result.

Key takeaway

Do not rank index drivers by stock percentage change alone. Pair each move with the applicable weight and the time period being measured.