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.
Live example: Quantustik's composite Market Conditions verdict as of 2026-07-20T02:00:27.290220+00:00 is “Caution”, one input to which is current market breadth. See the Market Conditions page for the full signal breakdown that breadth feeds into.
Breadth is one signal composed into the market conditions score alongside the VIX, credit spreads, the yield curve and sentiment — persistently narrow breadth nudges the market conditions toward caution and argues for smaller, more selective position sizing platform-wide, rather than trusting a rising index number at face value.
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.