Market breadth measures how many stocks participate in a market move, as opposed to how far a capitalization-weighted index moves. A rally carried by most stocks is broad; one carried by a handful of large companies is narrow.
How it works
A cap-weighted index such as the S&P 500 can rise while most of its members fall, because its largest companies carry the most weight. Breadth indicators count stocks instead of weighting them, so they show what the typical stock is doing. The main measures are:
- Advance/decline: the number of stocks that closed higher (advancers) and lower (decliners). Net advances are advancers minus decliners; the A/D ratio is advancers divided by decliners. The advance/decline line adds each day's net advances to a running total, so its slope shows whether participation is improving or fading over weeks.
- Share above moving averages: the percentage of stocks trading above their 50-day average (the intermediate trend) and their 200-day average (the long-term trend). These readings range from 0% to 100%.
- New highs and new lows: the number of stocks at 52-week highs against those at 52-week lows. A healthy advance usually shows a growing list of new highs.
- Derived indicators: the McClellan Oscillator (the difference between the 19-day and 39-day exponential averages of net advances) and up-volume versus down-volume compress the same information into a single line.
How to read it
Confirmation: when the index makes a new high and the A/D line, the share above the 50-day average and the count of new highs rise with it, the move is broadly supported.
Divergence: when the index makes a new high but fewer stocks join in, leadership is narrowing to a few names. Narrow rallies can continue for months, so a divergence is a warning about fragility rather than a sell signal. The reverse also matters: an index making a lower low while fewer stocks make new lows suggests selling pressure is easing.
Extremes: a very low share of stocks above their 50-day average (often cited as below 15–20%) reflects broad, indiscriminate selling. A rapid swing from very weak to very strong breadth, known as a breadth thrust, has historically been associated with the early stage of new advances. One example is the Zweig Breadth Thrust: the 10-day average of advancers ÷ (advancers + decliners) rising from below 40% to above 61.5% within 10 trading days.
Worked example (illustrative numbers)
Take a universe of 500 stocks on two days three weeks apart. On both days, the cap-weighted index closes higher, and on the second day it sets a new high.
| Measure | Day 1 | Day 2 |
|---|---|---|
| Index change | +0.8% | +0.5% (new high) |
| Advancers / decliners / unchanged | 320 / 170 / 10 | 210 / 280 / 10 |
| Net advances | +150 | −70 |
| Above 50-day average | 62% | 45% |
| At 52-week highs | 40 | 15 |
On day 1 the A/D ratio is 320 ÷ 170 ≈ 1.9 and the advance is broad. On day 2 the index rises to a new high while more stocks fall than rise, fewer than half sit above their 50-day average, and the count of new highs has shrunk. The gain is coming from a small group of heavyweights. That does not predict a decline, but it means the advance depends on fewer stocks, and a setback in those names would move the index sharply.
Limitations and common mistakes
- The universe matters. NYSE breadth includes many closed-end funds, preferred shares and other interest-rate-sensitive issues, so it can diverge from a list of operating companies.
- Daily counts are noisy. A single day's A/D reading says little; trends over weeks carry the information.
- Divergences can persist. Narrow markets led by large companies have lasted for extended periods.
- Breadth is not valuation. Broad participation says nothing about whether prices are cheap or expensive.
- Sector effects. A rate-driven move can lift or sink an entire group at once, which looks like a breadth shift but is really sector rotation.
In Clear Tape
The Market breadth card on the Today page is built from the most liquid US stocks in Clear Tape's screener, as of the last close. It shows the number of stocks advancing, declining and unchanged; the share above their 50-day and 200-day averages; the number at 52-week highs (a close within 0.5% of the high); the biggest gainers and losers; and the average change by sector, leaving out sectors with fewer than five stocks. It does not show 52-week lows or a cumulative A/D line.
The share of stocks above their 50-day average is also one of the six inputs to Clear Tape's fear and greed index. Market breadth is available to Tools and Pro members.
For educational purposes only. Not investment advice.