Why Breadth Matters More Than Price
In a market-cap weighted index like the S&P 500, Apple, Microsoft, NVIDIA, Amazon, Google, Meta, and Tesla control roughly 32% of the index. The S&P can make new highs driven entirely by 7 stocks while 493 go sideways or decline. That's a structurally fragile rally.
Every major market top in the last 50 years was preceded by breadth deterioration — the index making new highs while participation narrowed. The 2021 top saw the S&P peak in November while the average stock peaked in February. That 9-month divergence was visible only in breadth data.
The Four Core Breadth Indicators
1. Advance/Decline Line
The cumulative count of advancing stocks minus declining stocks each day. When the A/D line is making new highs alongside the index, breadth confirms the rally. When the index makes new highs but the A/D line doesn't follow — that's a negative divergence and the single most reliable warning of an impending correction.
Current: NYSE A/D line made a new all-time high last week, confirming the S&P 7,500 breakout. No divergence. The rally is structurally sound.
2. Percent of Stocks Above Key Moving Averages
| Metric | Current | Oversold | Neutral | Overbought |
|---|---|---|---|---|
| % above 200-DMA | 68% | <30% | 40–70% | >80% |
| % above 50-DMA | 74% | <25% | 35–65% | >80% |
| % above 20-DMA | 71% | <20% | 30–60% | >75% |
Interpretation: 68% above the 200-DMA is healthy. It's not yet at the 80%+ overbought readings that preceded pullbacks in mid-2023 and early 2024. Room exists for the rally to continue without breadth becoming dangerously stretched.
3. New 52-Week Highs vs New Lows
A simple but powerful indicator. In a healthy rally, new highs should outnumber new lows by at least 5:1. Readings above 100 new highs with fewer than 20 new lows indicate strong, broad participation.
Warning signal: When new lows expand above 40 while the index is still near highs, internal deterioration is underway. Currently: 87 highs / 14 lows = 6.2:1 ratio. Healthy.
4. McClellan Oscillator & Summation Index
The McClellan Oscillator measures the rate of change of breadth using exponential moving averages of the daily A/D data:
- Oscillator > +100: Short-term overbought. Momentum is strong but may need to consolidate
- Oscillator < -100: Short-term oversold. Snap-back rally likely within days
- Summation Index rising: Medium-term breadth trend is positive (current condition)
- Summation Index rolling over from above +500: Early warning that the breadth trend is deteriorating
Historical Divergences That Predicted Corrections
| Period | S&P Price Action | Breadth Signal | Outcome |
|---|---|---|---|
| Feb–Nov 2021 | S&P new highs into November | Average stock peaked Feb. A/D line diverged 9 months | -25% bear market (2022) |
| Jul–Sep 2023 | S&P near highs | % above 50-DMA fell from 82% to 48% while price held | -8% correction (Oct-Nov 2023) |
| Jan 2018 | S&P melt-up | New lows expanded; McClellan diverged | -10% in 9 trading days (Feb 2018) |
| Jul 2007 | S&P testing ATH | A/D line had been diverging since March. New lows expanding | -57% (2007-2009 GFC) |
Practical Breadth Monitoring Routine
- Weekly check (5 minutes): Pull up the NYSE A/D line chart alongside the S&P 500. Are both making new highs? If yes, rally confirmed. If the S&P is at highs but the A/D line is flat or declining, flag it
- Check % above 200-DMA: Free on StockCharts or TradingView. Above 65% = healthy. Below 50% on a rising market = divergence forming
- Count new highs/lows: Available on WSJ market data page. Ratio above 5:1 is positive. Below 2:1 is concerning
- McClellan Oscillator: Check for extreme readings (>+100 or <-100) for short-term timing
Current Assessment: May 2026
All four breadth indicators confirm the rally. The S&P 7,500 breakout is supported by broad participation — this is not a narrow Magnificent-7-driven move. The A/D line made new highs. 68% of stocks are above their 200-DMA. New highs outnumber new lows 6:1. The McClellan Summation is rising.
No divergence is present. Until breadth starts deteriorating while price continues higher, there's no structural reason to distrust this move. Combine with our Fear & Greed Index analysis and put/call data for the full picture.
Proflex tracks breadth daily as part of our composite sentiment model. When breadth divergences emerge, All-Access members receive alerts with specific hedging actions.