However good your stock is, most leaders pull back together when the broad market breaks. Statistically, a large share of any single stock’s movement is driven by the overall market’s direction. So seasoned traders ask, before picking a stock, "is this an environment worth buying in?" The core tool for that top-down judgment is market breadth.
The index alone isn’t enough
Indexes like the S&P 500 or KOSPI are dominated by a few mega-caps. A handful of large stocks can lift the index while most others fall — an illusion of strength. That’s how you get an index at new highs with nothing worth buying underneath. The market’s true health shows in what hides behind the index: how many stocks are rising together.
Gauges of breadth
- Advancing-stock ratio: the share of stocks rising (or trending strongly). The higher it is, the more broad-based and healthy the advance.
- New highs vs. new lows: 52-week new highs minus new lows. Positive and rising is strong; turning negative is a warning.
- Number of passing stocks: how many names clear the eight conditions each day in Trend Screener. A rising count means more leaders; a sharp drop means the broad trend is weakening.
Divergence — the trap in an index at new highs
Breadth earns its keep when it points the opposite way from the index. The U.S. market in late 2021 was the textbook. The indexes kept printing record highs into November and December — while beneath the surface, 52-week new lows expanded week after week and a large share of mid- and small-cap growth stocks were already down 30–50% from their peaks. Breadth broke first; a shrinking club of mega-caps held the index up. The 2022 bear market followed within months, and to anyone watching breadth it did not arrive out of nowhere. The same anatomy — a narrow advance masking broad deterioration — repeats in every market and every cycle, which is why the divergence check belongs in the weekly routine.
Scale aggression to the regime
Combine breadth with the index trend and you can roughly read the regime.
- Attack: index rising above its 200-day, advancing ratio and passing counts climbing. Press leader breakouts.
- Neutral / caution: the index holds but breadth deteriorates (only mega-caps rise). Cut new buys and tighten stops.
- Defense: index below the 200-day, new lows expanding. Most breakouts fail — raise cash and wait.
The Follow-Through Day — confirming a bottom
The hardest call in trend following is when defense turns back into attack. William O’Neil’s Follow-Through Day (FTD) is the classic confirmation device. The skeleton of the rule: after a decline, a rally attempt begins; on day 4 or later of that attempt, a major index rises strongly — roughly +1.5–2% or more — on volume heavier than the prior day. That combination is read as institutions confirming the turn. The April 2020 follow-through shortly after the COVID crash low, and the follow-through after the October 2022 bear-market low, each marked the launch of a new cycle.
The honest caveat: FTDs fail — bear-market rallies produce them too. So the practical protocol is graduated: after a follow-through, start with pilot positions and scale up only as new breakouts actually hold. More important than the exact rule is the posture it encodes — raise aggression only after the market has confirmed the turn, and let the evidence accumulate before committing fully.
TSS — how this site scores breadth
Trend Screener’s Market page distills these lenses into a single Trend Strength Score (TSS, 0–100) — a composite recomputed after every close from breadth, trading-value flows, and index structure. The direction matters more than the level: a score climbing steadily off a floor says the attack regime is approaching; a score rolling over from the top with the breadth component fading first is the divergence pattern above, in real time. It’s computed independently for the U.S. and Korean markets, so the temperature gap between the two is visible at a glance.
Trend Screener’s market-environment page
The market page charts several KPIs daily — passing-stock counts, average relative strength, breadth, new-high trends. Checking their direction before picking individual names helps you judge whether it’s time to press breakouts or to reduce risk and wait. Trend following performs best when strong selection meets the right market timing.
Frequently Asked Questions
Do I need to check breadth every day?
The multi-week direction matters more than any single day. You don’t need a daily ritual — but on any day you’re considering a new buy, check it first. "Right stock, wrong market" is one of the most common ways good setups fail.
How do I trade a market where only the index rises?
Two adjustments. First, restrict new entries to the narrow group actually carrying the market — outside it, breakout failure rates soar in a narrow tape. Second, run fewer and smaller positions than usual. If the narrow advance broadens into a healthy one, you can scale up then; nothing is lost by waiting for confirmation.
What happens when a Follow-Through Day fails?
The index undercuts its low and the rally attempt is void. This is exactly why you start with pilot positions — a failed FTD costs a couple of small stops, and you wait for the next attempt. Market bottoms are less a single event than a process of several attempts, one of which finally holds.
Breadth is strong but my stock keeps lagging — what gives?
Then the problem is the stock, not the market. Lagging a broad advance means low relative strength — by definition, not a leader. In exactly these phases you should rotate toward high-RS names passing all eight conditions. See the relative strength guide.