What Is Expectancy, and Why It Matters More Than Win Rate

TL;DR:Expectancy, not win rate, is the number that actually tells you whether a strategy makes money over time; it combines how often you win and lose with how much each outcome is worth. A strategy with positive expectancy is worth continuing through a losing streak; one with negative expectancy will eventually lose money no matter how good any single trade felt.

“What’s your win rate” is one of the most common questions asked about a trading strategy, and it’s the wrong one to obsess over on its own. A strategy that wins 80% of the time can still lose money overall. A strategy that wins only 35% of the time can still be genuinely profitable. The number that actually decides which is called expectancy.

What Expectancy Actually Measures

Expectancy is the average amount you can expect to make or lose per trade over time, calculated as (win rate × average win) minus (loss rate × average loss). It combines how often you’re right with how much you make when you are, against how often you’re wrong and how much that costs you.

A Purely Illustrative Example

Not real data, just to show the shape of the idea: a strategy that wins 40% of the time, with average wins twice the size of average losses, has a positive expectancy, it makes money over a large enough sample despite losing more often than it wins. A strategy that wins 70% of the time but risks three times as much as it makes on each win can still have negative expectancy. Win rate alone tells you almost nothing without knowing the size of the wins and losses next to it.

Why This Number Should Actually Drive Your Decisions

A strategy with positive expectancy is worth continuing to execute even after a losing streak, because the losing streak is expected noise around a favourable average, not proof the strategy stopped working. A strategy with negative expectancy will eventually lose money no matter how good any individual trade inside it felt.

You Can’t Calculate This Without a Journal

Expectancy isn’t something you can estimate from memory or gut feeling, it requires real logged trades: actual wins, actual losses, actual sizes, over a meaningful sample. That’s a direct, practical reason a trading journal earns its place, not as a nice-to-have habit, but as the only honest way to know whether a strategy is actually working.

Sample Size Changes What You Can Trust

Expectancy calculated from ten trades tells you very little, because a handful of trades can easily be dominated by ordinary variance rather than the strategy’s real average behaviour. A meaningful expectancy figure needs a large enough sample, often several dozen trades at minimum, before the number starts to reflect the strategy itself rather than a lucky or unlucky short stretch.

This is part of why judging a strategy after five or ten trades, in either direction, tends to be premature. A strategy that looks great over a small sample can regress once the sample grows, and one that looks disappointing over a small sample can turn out to have solid expectancy once enough trades are logged to actually see it.