Market Breadth

Several breadth indicators measure different aspects of market participation:

Advance/Decline Line (A/D Line): The cumulative sum of (advancing stocks - declining stocks) each day. When the A/D line is rising, more stocks are going up than down — broad participation confirms the uptrend. When the index makes new highs but the A/D line does not, it signals narrowing leadership and a fragile rally.

Advance/Decline Ratio: The ratio of advancing to declining stocks on a given day. Values above 2:1 indicate strong buying across the market. Values below 1:2 indicate broad selling. Extreme readings show unusually one-sided sessions; on their own they are not reversal signals.

New Highs vs. New Lows: The number of stocks making 52-week highs minus those making 52-week lows. In a healthy bull market, new highs consistently outnumber new lows. When the index rises but new highs are shrinking, the rally is losing participants.

Percentage Above 200-Day Moving Average: The percentage of stocks in an index trading above their 200-day moving average. StockCharts treats readings above 50% as a bullish bias and below 50% as bearish, with readings above 70% or below 30% often called overbought or oversold.

Percentage Above 50-Day Moving Average: A shorter-term breadth measure. Useful for identifying intermediate-term breadth thrust signals. A fast jump from deeply oversold to strong readings is one form of breadth thrust.

McClellan Oscillator: The difference between the 19-day and 39-day exponential moving averages of net advances (advancing minus declining issues). Positive readings indicate improving breadth; negative readings indicate deteriorating breadth.

Breadth divergences are among the most widely watched warning signs in technical analysis, but they are not timing signals. They occur when the headline index moves in one direction while breadth indicators move in the opposite direction.

Bearish breadth divergence: The S&P 500 makes a new all-time high, but the A/D line fails to confirm — it is below its previous peak. This means fewer stocks are participating in the rally. The index is being propped up by a small number of large-cap stocks (NVDA, AAPL, MSFT, etc.) while the average stock is actually declining.

Bullish breadth divergence: The market index makes a new low, but the A/D line makes a higher low. More stocks are actually turning up even though the index-level picture looks bearish. This often marks the end of a correction, as the majority of stocks have already bottomed even if the cap-weighted index has not.

Timeframe matters: Daily breadth divergences can persist for days or weeks — they are not immediate timing signals. The divergence tells you the trend is weakening, not exactly when it will reverse. Combine breadth divergences with other signals (VIX spikes, volume climaxes, support/resistance levels) for timing.

Sector breadth: Apply the same analysis to individual sectors. If the technology sector index is rising but fewer tech stocks are participating, the sector rally is narrow and vulnerable. This is especially useful for sector rotation decisions.

As a risk management filter: When breadth is strong (A/D line rising, >60% of stocks above 200 DMA), take full-size positions and be aggressive on breakout entries. When breadth is deteriorating, reduce position sizes and tighten stops. Backtest the overlay before relying on it: it can cut exposure in narrow markets, but it can also reduce size just before a rally.

Breadth thrust signals: When breadth surges from extremely oversold to overbought in a compressed timeframe, it produces a rare breadth thrust signal. The classic Zweig Breadth Thrust requires the 10-day advance/decline ratio to move from below 0.40 to above 0.615 within 10 trading days. Signals are rare: StockCharts' Arthur Hill counted eight NYSE signals in the 40 years to January 2019, and the NYSE Composite still made a new low after the October 2015 signal.

Confirming breakouts: Before entering a long trade on an individual stock, check whether market breadth supports the entry. A stock breaking out to new highs while the A/D line is declining is swimming against the tide — the probability of the breakout failing is elevated.

Identifying market regimes: Breadth indicators help classify the current market environment. Strong breadth + rising index = healthy uptrend (trade with confidence). Weak breadth + rising index = late-stage rally (trade cautiously, tighten stops). Strong breadth + falling index = correction within uptrend (look for buying opportunities). Weak breadth + falling index = bear market (defensive positioning).