S&P 500 Market Breadth Deteriorates as Equal-Weight Lag Signals Rising Concentration

Market breadth across major U.S. equities is weakening again, with only 44% of S&P 500 constituents currently trading above their 50-day moving average—marking the lowest level since April.
The share of stocks holding above that key short-term indicator has dropped 14 percentage points since mid-August. Over the same timeframe, the share of index components trading above their 200-day moving average declined by 10 percentage points to 64%, hitting its lowest mark since June.
The divergence is also evident in index performance: the S&P 500 Equal Weight Index fell 2.9% across this stretch, compared to a milder 1.4% decline in the headline market-cap-weighted S&P 500.
The growing spread between equal-weighted performance and the cap-weighted benchmark underscores that market gains are increasingly concentrated in a shrinking group of mega-cap leaders.