Market cap change measures today's move in absolute dollars — a 2% gain on a mega-cap moves more shareholder value than a 20% spike on a small-cap. This heatmap colors US stocks by daily market-cap change, sized by market cap and grouped by sector.
Greener tiles added the most dollar value today, redder tiles destroyed the most.
Percentages flatter small-caps — a micro-cap can gain 40% and move the market less than a mega-cap gaining 0.5%. Dollar change shows where shareholder value actually moved.
A genuine event at scale — earnings surprise, guidance raise, or a sector-wide re-rating concentrated in the largest names.
Same colors, different denominator — percent answers "who moved most relative to size", dollar answers "who moved the most value".
Heatmap data updates through the trading session. Fundamentals come from Finnhub and SEC filings; scores are simplified heuristics for screening — not investment advice.