Core terms
Win rate
The share of trades that end as wins under a stated definition of a win. It is one input to expectancy and says little about profitability on its own.
Win rate counts how often a process wins, not how much. A log of 20 trades with 12 wins (60%) averaging +$40 and 8 losses averaging −$55, with $3 of costs per trade, has an expectancy of −$1.00 per trade, or −0.02R at $50 risk (Illustrative).
The same point holds the other way. A process winning 70% of the time at +0.45R and losing 30% at −1.25R averages −0.06R per trade; one winning 40% at +1.90R and losing 60% at −1.10R averages +0.10R (Illustrative, after costs). Exit rules move win rate and average win in opposite directions: taking profits earlier usually raises the first and lowers the second.
What traders should verify
Report win rate together with average net win, average net loss, the scratch share and the number of trades. Compare it with the breakeven win rate for the same plan.
Do not conflate
Trader usage; there is no official definition. Tools differ on how scratches and gross-flat trades that lose fees are classified, which changes the figure. A win rate from 20 or 30 trades has a wide interval.
Primary source
Trader usage: there is no official definition, and platforms and tools may calculate it differently.