Market Breadth Indicators
Market breadth measures the degree of participation in a market move. A rally driven by broad participation across many stocks is fundamentally different from one concentrated in a handful of mega-cap names. Breadth indicators help traders distinguish between healthy advances and narrow rallies that may be vulnerable to reversal.
Advance/Decline Line
The advance/decline (A/D) line is the most fundamental breadth indicator. It is calculated by taking the number of advancing stocks minus the number of declining stocks each day and adding the result to a cumulative running total.
Interpretation: When the A/D line confirms new highs in the index, the rally has broad participation. When the index makes new highs but the A/D line fails to confirm (a bearish divergence), the rally is narrowing, a condition read as a warning.
The 2021-2022 market provides a textbook example. The S&P 500 continued making new highs into early January 2022, but the A/D line peaked months earlier, correctly signaling that fewer stocks were participating in the advance. The subsequent correction affected the broad market, with the average stock declining far more than the index.
New Highs / New Lows
This indicator counts the number of stocks making new 52-week highs versus new 52-week lows. It is particularly useful at market extremes.
Bullish Signals: A healthy rally produces expanding new highs and contracting new lows.
Bearish Signals: If the index is near highs but new highs are contracting while new lows are expanding, the reading is internal deterioration. A cross where new lows exceed new highs while the index is still relatively elevated is read as a warning signal.
Washout Signals: Extremely high new-low readings during a selloff are read as capitulation, a possible selling climax.
Percentage of Stocks Above Moving Averages
This measures what percentage of stocks in an index trade above a specific moving average (typically the 50-day or 200-day). It provides a snapshot of the market's internal health.
Above 200-day MA: Readings below 30% are conventionally read as broad technical damage, and readings above 85% as an overbought condition.
Above 50-day MA: This is more sensitive and useful for shorter-term analysis. Sharp drops below 25% are read as possible short-term selling climaxes.
McClellan Oscillator
The McClellan Oscillator is a momentum indicator derived from the A/D line. It measures the difference between the 19-day and 39-day exponential moving averages of daily net advances. Readings above +100 indicate a strongly overbought breadth condition. Readings below -100 indicate oversold conditions.
The McClellan Summation Index is the cumulative total of the oscillator and provides a longer-term view of breadth trends. A rising summation index is read as a healthy intermediate-term trend.
Sector Participation
Beyond individual stock breadth, sector-level participation matters. A rally led by cyclical sectors (financials, industrials, materials) suggests economic confidence, while a rally concentrated in defensive sectors (utilities, staples, healthcare) may signal risk aversion despite rising prices.
Tracking the number of S&P 500 sectors making new highs is a simple breadth measure: more of the 11 sectors trending higher means broader participation, fewer means narrower leadership. Our free sector rotation heatmap publishes that participation directly, with breadth and dispersion readings next to the intraday sector ranking.
Applying Breadth to Trading
Breadth indicators work as confirmation or divergence tools rather than standalone signals:
- Breakouts: a breakout on expanding breadth has broader participation behind it
- Tops: breadth divergences have appeared ahead of price peaks, as in the 2021-2022 example above
- Pullbacks: oversold breadth readings in an uptrend describe a washed-out market, not a buy signal
- Risk: narrowing breadth means fewer stocks are carrying the index, even if the index appears strong