Every trader who’s had a good month has asked themselves the same question: is this skill, or luck? It matters enormously — because acting on an edge that isn’t real is how accounts blow up, and abandoning an edge that is real, after a normal losing run, is how good traders quit too early.
Here’s how to answer it honestly.
Win rate tells you almost nothing
A 70% win rate sounds great until you learn the wins are tiny and the losses are huge. A 40% win rate sounds bad until you learn the winners are three times the size of the losers. The number that actually matters is expectancy.
Expectancy: the one number that counts
Expectancy is the average amount you can expect to make per trade over many trades:
Expectancy = (Win rate × Average win) − (Loss rate × Average loss)
Positive expectancy means the system makes money on average; negative means it bleeds no matter how disciplined you are. Try the expectancy calculator with your own numbers.
Sample size is where most traders fool themselves
Here’s the uncomfortable truth: a great-looking expectancy over 20 trades can easily be luck. Rough guidance:
- 30 trades — a first read, treat with suspicion.
- 100 trades — enough to start acting on.
- More if your win/loss sizes vary a lot.
Why a confidence interval beats a point estimate
A single expectancy number hides how uncertain it is. A Wilson confidence interval puts a range around your win rate given your sample size — so instead of “45% win rate”, you get “45%, and I’m 95% confident the true rate is between 36% and 54%.”
That range is what tells you whether a losing streak is signal (your edge decayed) or noise (normal variance around a real edge). It’s the difference between calmly continuing and panicking out of a profitable system.
Measure it continuously, not once
An edge isn’t a one-time verdict — it drifts as markets and your execution change. The traders who last measure their expectancy and its confidence interval live, from every real trade, so they catch decay early and don’t abandon a good system after a bad week.
Related: trading expectancy explained · what is an R-multiple · risk/reward calculator.