Investing term
What is Mean reversion?
The tendency of valuations and margins to return to long-run averages over time.
Mean reversion is the tendency of things stretched far from their long-run average — valuations, profit margins, returns — to drift back toward it over time. It's driven by competition and cycles: sky-high profit margins attract rivals who compete them down, while depressed ones drive out competitors until the survivors recover.
It's a powerful counterweight to the human instinct to extrapolate the recent past. When a company's margins or a market's valuation reach extreme highs, the natural assumption is that they'll continue — but mean reversion warns they're more likely to fall back. The same works in reverse for extreme lows. Mean reversion doesn't say when or by how much, and some things genuinely don't revert — a company with a durable moat may sustain high margins, and a business in secular decline may never recover. But as a default expectation, betting against extremes reverting is often a losing game.
Sky-high margins attract competitors that compete them down; depressed ones recover. Mean reversion is the antidote to extrapolating extremes — though moats and secular change are the real exceptions.
For example
A company's profit margins hit a record high as demand booms; competitors pile in, and over the next few years margins drift back toward the industry's long-run average — mean reversion at work.
Learn it by doing
That's Mean reversion in theory — it clicks when you use it. Practise it hands-on in a free, interactive lesson (Stage 15, Valuation for Investors).
Try the free lesson →Why it matters to you
Mean reversion matters because it's the antidote to extrapolating extremes, which is one of investing's most common and costly errors. Paying a premium for a company at peak margins, or writing off one at trough margins, both bet that the extreme will persist — when history says it usually reverts. Building the expectation of reversion into your thinking guards against overpaying at the top and panicking at the bottom, though it must be balanced against the cases (moats, secular change) where things genuinely don't revert.
⚠ Assuming everything always reverts
Mean reversion is a tendency, not a law. A company with a genuine moat can sustain high margins indefinitely, and a business in secular decline may keep falling with no reversion. Blindly betting that every extreme will snap back — buying every fallen stock as a bargain, shorting every high-margin winner — ignores the durable exceptions and can be a value trap. Distinguish temporary extremes from structural change.