The break-even win rate formula
If you risk 1R to make an average of X R, you break even when your wins exactly pay for your losses.
At 1:1 you need to win 50% of trades. At 1:2 you need 33.3%. At 1:3, only 25%. That is why traders with modest win rates can still be very profitable, and why a high win rate means nothing on its own if the losses are bigger than the wins.
What expectancy tells you
Expectancy is the average amount you make or lose per trade, measured in R. It combines your win rate and R:R into one number that tells you whether a strategy actually has an edge.
A 45% win rate at 2R gives (0.45 × 2) − 0.55 = +0.35R per trade. Over 100 trades at 1% risk, that is roughly +35% before costs. A 60% win rate at 0.5R gives (0.6 × 0.5) − 0.4 = −0.10R, which loses money despite winning most trades.
Use your real numbers, not your planned ones
Most traders plan for 1:3 and then close winners early, so their real average R:R is closer to 1:1.5. Their break-even win rate quietly jumps from 25% to 40%. The only way to know your true expectancy is to log every trade with its actual result in R, including the ones you would rather forget.
Spreads, commission and swap also come off every trade. If your edge is only a few points above break-even, costs can wipe it out.