What is market breadth?
An index is an average, and averages hide things. In a cap-weighted index such as the S&P 500, the biggest companies carry the most weight (see stock market indexes), so the index can make new highs while the typical stock does not. Breadth asks the other question: how many stocks are rising with it?
Broad participation means most stocks and sectors rise together. Narrow leadership means a shrinking group does the work. Many traders see narrow rallies as more fragile, because a stumble in a few leaders has little underneath to absorb it. It is a warning, not a forecast: narrow markets can keep rising for a long time.
- Market breadth
- How many stocks take part in a market move, measured by counts such as advancers vs decliners or the share of stocks above a moving average.
- Advance/decline line
- A running total of advancing stocks minus declining stocks, day after day. Its direction and peaks matter, not its level.
- Breadth divergence
- The index and a breadth measure disagree: for example, the index makes a higher high while the A/D line makes a lower high.
How does the advance/decline line work?
Each day, count the stocks in an exchange or index that closed up (advancers) and down (decliners). The A/D line adds each day’s net figure, advancers minus decliners, to the previous total. It rises when more stocks go up than down and falls when the reverse is true; its level depends on the start date, so read its direction and peaks.
Hypothetical, in the table below: day 1 nets +900, day 2 −500, day 3 +300. On day 4 the index rises 0.2% but 2,000 stocks fall and only 1,300 rise, so the line drops to 0. One such day means little; weeks of them while the index climbs form the divergence at the top of this page.
A bearish divergence is an index at a higher high with the A/D line at a lower high; a bullish divergence is an index at a lower low with the A/D line at a higher low. Either can last for months, or never resolve the way it suggests.
What percentage of stocks are above their 200-day moving average?
This gauge counts the share of an index’s members trading above their own 200-day moving average, a common dividing line between long-term uptrends and downtrends. On TradingView, S5TH tracks it for the S&P 500, and S5FI does the same with the 50-day average, which reacts faster and swings more often.
Above 50% means most stocks are in long-term uptrends. Readings above about 70% are often called broad strength and below about 30% widespread weakness; these are conventions, not rules. The useful signal is a mismatch, as in the drawing below: the index near its high while only 42% of its stocks are above their 200-day average.
New highs vs new lows
Another count compares stocks making new 52-week highs with stocks making new 52-week lows. In a healthy advance, new highs outnumber new lows and their number grows as the index climbs. When the index sets a record while the list of new highs shrinks and new lows creep up, fewer stocks are leading. Some traders follow the difference, new highs minus new lows, as a single line.
Equal-weight vs cap-weight: comparing RSP and SPY
An equal-weight index gives every member the same weight, so the smallest company counts as much as the largest. The S&P 500 Equal Weight Index works this way and is rebalanced quarterly; Invesco’s RSP is an ETF that tracks it, while SPY tracks the regular cap-weighted S&P 500. Both are named as instruments, not recommendations.
Comparing the two is a quick breadth check. If the cap-weighted index rises while the equal-weight version goes nowhere, the typical stock is lagging and a few giants are doing the lifting, as drawn below. When the equal-weight line keeps pace or leads, participation is broad. Charting RSP/SPY on TradingView shows the gap as one line.
How do traders use market breadth?
As context, not as a buy or sell signal. Breadth tells you what kind of market you are in; it rarely tells you the day a trend will turn. Common uses:
- Confirm the trend: an index rising with a rising A/D line and a growing share of stocks above their 200-day average has broad support, one of the traits of healthy phases described in bull vs bear market.
- Spot narrow leadership: an index at a high with falling breadth is a reason to tighten risk, not a reason to sell short.
- Read washouts: after a sharp drop, very low readings show that selling was widespread. Check them alongside the VIX, and remember both can stay extreme for weeks.
- Adjust size: when breadth is weak, many traders hold fewer and smaller long positions; risk management and the position size calculator keep the dollar risk fixed.