Breadth basics

The index can rise while most of the stocks in it fall. That happens when a handful of very large companies carry the average. The trend filter would read "uptrend", and yet a swing trader buying breakouts across the market would be picking from a list where most names are quietly rolling over. Breadth is the check that catches this. It asks: how many stocks are actually participating?

Three breadth measures worth knowing

You do not need a dozen. Three cover the ground, and all are free on most charting platforms.

1. Percentage of stocks above their 50-day MA. Published for the S&P 500 and other indices. It runs from 0 to 100.

Reading	Interpretation
Above 70	Broad participation; strong but can be stretched
40 to 70	Healthy; most of the year lives here
20 to 40	Narrow market; index may be rising on a few names
Below 20	Washed out; the best long entries in history start from here

2. New highs minus new lows. Count of stocks making 52-week highs minus those making 52-week lows, usually as a daily figure or a 10-day average. Positive and expanding confirms an uptrend. Negative while the index is near highs is the classic warning.

3. Advance-decline line. Cumulative sum of daily advancers minus decliners. You do not read its level; you read whether it is making new highs along with the index. If the index makes a new high and the A/D line does not, the rally is narrow.

How to read them

Breadth is a confirmation tool. It sharpens the regime label rather than replacing it.

Index                          % above 50 MA
      ___/‾‾  new high               ‾‾\___
 ___/                          ___/       \___  lower high
                              
"uptrend" by the filter        but fewer stocks participating

Trend filter	Breadth	Adjusted regime	Action
Uptrend	Expanding or > 60	Confirmed uptrend	Full size
Uptrend	Contracting or < 40	Narrow uptrend	Half size, stick to leaders only
Correction	Below 20	Washout	Watch for reclaim setups
Downtrend	Any	Downtrend	No new stock longs

The narrow-uptrend case is the one that matters most. The filter says yes, breadth says careful. The resolution is to trade only the names that are actually leading, at reduced size, and to expect more failed breakouts than usual.

Breadth thrusts and washouts

Two extremes deserve a note because they are the moments swing traders make most of their year.

A washout is when the percentage above the 50 MA falls under 20 and new lows swamp new highs. It usually arrives with an index below its 50 MA and frightening headlines. It is also where the failed-breakdown setup (Module 4, lesson 3) does its best work, because everything that was going to be sold has been sold.

A breadth thrust is a rapid move from washed-out to broad participation, for example the percentage above the 50 MA going from under 20 to over 60 in a few weeks. It marks the start of the early-recovery regime and is the signal to begin rebuilding a long book at half size, then full size once the 50 MA turns up.

Key idea: The index tells you the direction of the tide. Breadth tells you how many boats are rising with it. Trade only when both agree, and smallest when they disagree.

For other markets

Breadth is a stock concept, but the idea travels. In crypto, compare BTC's trend with the share of the top 50 coins above their 50-day averages; an altcoin rally that BTC is not confirming is narrow in the same way. In futures on a single index, there is no breadth in the contract itself, but the underlying index's breadth still tells you whether a breakout is likely to hold. In forex, the equivalent is whether a currency is strong against most other currencies or only against one.

Keep it simple

The temptation with breadth is to collect indicators until they contradict each other. Pick the percentage above the 50 MA as your primary reading, glance at new highs versus new lows, and check the A/D line only at index highs. Write the primary reading in your weekly checklist every weekend. After a few months you will know what "normal" looks like and the abnormal readings will announce themselves.

Try it: Find the percentage of S&P 500 stocks above their 50-day MA on your platform. Note today's reading, then scroll back to the last time the index made a new high. Was breadth higher or lower than at the previous high? Write one sentence on what that implied for breakouts in the weeks that followed.

Recap

Breadth measures how many stocks are participating in an index move.
Use the percentage above the 50-day MA as the primary reading; new highs minus new lows and the A/D line as confirmation.
An uptrend with contracting breadth is a narrow uptrend: half size, leaders only.
Washouts under 20% precede the best reclaim setups; breadth thrusts mark the start of new uptrends.
Record one breadth reading every weekend so abnormal readings stand out.