The Advance-Decline Line Manual

Research note. Every figure computed at render from our daily breadth dataset (2010–present, ~4,750 US common stocks) — the same file behind the live A/D line tracker. Methods in How we checked it; editorial standards in How we use AI.

What is the advance-decline line?

The simplest breadth measure there is: count the stocks that rose today, subtract the stocks that fell, add the result to yesterday's running total. That running total is the A/D line. When it rises with the index, the advance is broad; when the index climbs while the line stalls, fewer and fewer stocks are doing the lifting. Ours is computed across roughly 4,750 US common stocks — as of August 4, 2026, 3,396 advanced and 1,351 declined, putting the cumulative line at 126,626 against its all-time high of 183,643 set June 11, 2021.

Is breadth confirming the market right now?

As of the August 4, 2026 session: 3,396 stocks advanced, 1,351 declined — a net of +2,045. SPY sits 0.0% from its high. The verdict comes from the top-500 cohort line (the aggregate has sat below its June 2021 peak for years on structural small-cap drift — the decomposition below is this page's whole argument): that line last peaked in April 2026, 73 sessions ago, so our read is a divergence worth watching — the index is near its high without large-cap breadth. The small-cap tail's line peaked June 2021 and remains the weak cohort. The tracker updates all of this after every close.

How the line is built — and why levels lie

Each day is one number: advancers minus decliners, regardless of size — Apple and the smallest Russell name each get one vote. That equal vote is the whole point (it measures participation, not capitalization) and also the line's oldest weakness: the universe itself drifts. Stocks delist, IPOs arrive, and the classic NYSE version famously counts bond funds and preferreds among its "stocks." Ours restricts to US common stocks to cut that noise, and still inherits drift — which is why the line's level against 2021 is partly a statement about universe composition, not only about markets. Direction over weeks, and agreement with price at the highs, are the readings that survive this caveat.

The divergence record — breadth peaked first, every time

The lore says breadth leads price at tops. Our record agrees, with a spread of lead times worth seeing plainly. For each major SPY top since 2010, here is when the A/D line made its peak:

Four for four — and honesty requires the other half of the sentence. The leads ranged from three weeks to seven months, which is far too wide to time anything with; and the line has also stalled without a top following. The tracker page runs the systematic version — every unconfirmed high, not just the famous ones — and the honest answer is that divergence is a condition that precedes trouble, not a schedule for it.

Where the weakness lives — the cohort decomposition

One line hides its own composition, so we also compute the A/D line in three market-cap cohorts: the top 500 names, the middle 1,500, and the tail of everything smaller. The decomposition answers the question the aggregate can't: the top-500 line made a fresh all-time high in April 20, 2026, while the tail's line peaked June 11, 2021 and has bled to -70,642 — negative since the aggregate's 2021 high. The famous "weak breadth" of this cycle is specifically small-cap and micro-cap breadth; among the stocks most people actually own, participation has been fine.

Where this gauge will mislead you

• Levels across eras mean nothing. The line's value is a running sum from an arbitrary start; universe drift compounds it. Compare direction and divergence, never the number itself.
• Divergences don't time tops. Three weeks to seven months of lead in our own record. A divergence says conditions have narrowed — it does not say when narrowness matters.
• Every A/D line is a universe choice. NYSE-composite lines include bond CEFs and preferreds; ours excludes them but inherits common-stock delisting drift. Cross-site comparisons are usually comparing universes, not markets.
• One vote per stock cuts both ways. Equal weighting is the feature — and it means the line can diverge for structural reasons (a bleeding micro-cap tail) while the investable market is healthy. The cohort chart above is the antidote.

The last 12 sessions

Full daily dataset: ad_line.json.

How we checked it

Advancers and decliners are counted daily across our common-stock universe (the same computation the tracker charts); the cumulative line and the cohort lines come straight from that file. Divergence leads are computed by finding the line's highest close in the year up to each named market top — the dates and session counts in the table recompute at render, so data revisions flow through. The named tops are the S&P 500's closing cycle highs.

Frequently asked questions