A Stock Can Rise 5% and Barely Move the Index. Why?
A large percentage move from a low-weight stock can contribute less than a small move from a high-weight stock.
Read the draftWeighted Impact & Market Intelligence
Why Do the Biggest Movers Differ From the Biggest Contributors?
A stock's own percentage move and its weighted impact answer different questions. Compare both with a clear hypothetical example.
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A Biggest Movers list ranks the securities that moved most by its chosen measure. The biggest index contributors may be elsewhere because a smaller move in a high-weight stock can matter more to the benchmark.
What each list measures
A mover ranking needs a defined unit: percentage return, dollar price change, or another metric. A contributor ranking applies the index's weighting method to a same-period move. Mixing these lists without showing the unit can make a quiet large constituent look less important than it was.
A two-stock example
Hypothetical cap-weighted index: Stock A has a 1% weight and rises 10%, contributing approximately +0.10 percentage points. Stock B has an 8% weight and rises only 2%, contributing approximately +0.16 percentage points. A wins the percentage-mover list; B contributes more to the index estimate.
The units matter: +10% is A's return; +0.10 percentage points is its estimated contribution to the index return. To estimate index points, multiply that contribution expressed as a decimal by the starting index level.
What can change the ranking
Weights change over time, and a selected basket omits other index constituents. Data-feed timestamps can also put a stock card and an index reading on different clocks. For the Dow, a price-weighted calculation must replace the cap-weight multiplication. Use the app's Impact and Biggest Movers views as complementary comparisons, not interchangeable leaderboards.
Key takeaway
The most dramatic stock chart is not automatically the largest index driver. Compare the stock's move with its applicable influence.
Sources and further reading
- S&P DJI Index Mathematics MethodologyOfficial index calculation and divisor reference
- Dow Jones Averages MethodologyOfficial Dow 30 price-weighting methodology