Market breadth measures how many stocks are actually participating in a market move — commonly, the percentage of S&P 500 constituents trading above their 200-day moving average.
An index-level number can mask what is happening underneath: a few large names can carry the index higher while the median stock lags. When leading names stumble, a narrow rally has fewer other stocks to cushion the index.
A breadth thrust (the Zweig Breadth Thrust) is a rare, rapid swing from narrow, pessimistic participation to a broad, sudden surge of advancing stocks within a short window — historically one of the more bullish, if infrequent, momentum signals.
One common way: the percentage of S&P 500 constituents trading above their own 200-day moving average.
If only a handful of large stocks drive an index higher, the rally is more fragile when those leading names stumble.
A rare, rapid swing from narrow participation to broad, sudden buying across many stocks — historically bullish, if infrequent.
Browse all S&P 500 tickers to see this metric applied to individual companies.
Educational research only — not investment advice.