About this tool
The Break-Even Win Rate Calculator shows the minimum share of your bets that must win, at a given price, just to break even over the long run. That threshold is simply the odds' implied probability: break-even win rate = 1 / decimal odds, expressed as a percentage. For the classic American −110 line the decimal price is 1.909, so you must win 52.38% of the time to stop losing money — anything less and the vig grinds your bankroll down.
Everything is computed locally in your browser; nothing you type is sent anywhere. Enter odds in American, decimal, or fractional format and the tool converts internally before taking the reciprocal. You can also enter a target ROI: the win rate required to earn a return r is (1 + r/100) / decimal odds, which is always higher than the plain break-even. Finally, enter your actual observed win rate and the tool reports the margin (actual − break-even) — a positive margin means you are beating the price.
This is a pure math reference and does not handle real money or place any wagers. It assumes flat, independent bets at a single price; parlays, varying stakes, and correlated outcomes change the picture. Use it to sanity-check whether a strategy's hit rate can plausibly overcome the odds it is being played at.