Breakeven win rate = 1 / (1 + payoff ratio). At a payoff of 3, you need 25%. At 2, 33.3%. At 1.5, 40%. At 1, 50%. At 0.5, 66.7%.
Two uses. Before trading a system, compute the bar and ask honestly whether the setup clears it; a 3:1 target needing only 25% accuracy is easier to defend than a 0.8:1 scalp needing 56%. After trading it, compare realised win rate against the bar to see how much room the edge actually has - a system needing 40% and delivering 43% is real but fragile, and one bad month of execution erases it.
Add costs before judging. With a slippage-budget worth 0.1R per trade, a nominal 2:1 payoff is really about 1.8:1, which lifts the breakeven bar from 33.3% to 35.7%. Small on paper, decisive over hundreds of trades.
Related: payoff-ratio, win-rate, expectancy-per-trade, slippage-budget