Implied probability and break-even win rate

What the number means

Break-even win rate is the share of bets you must win at that price simply to end up level. At -110 it is 52.38%, so 52 wins in 100 is a losing month and 53 is a thin winning one. The gap between 50% and that break-even figure is the operator's cut, and it is the reason coin-flipping loses money slowly rather than breaking even.

The second question the page answers is the one that actually decides a bet: at this price, what win rate would you need for the bet to be worth making? If you want a 5% return on stake at -110, you need (1 + 0.05) / 1.9091, which is 55.0%. Whether you can identify bets you win 55% of the time is not something a calculator can tell you.

Where it misleads

Break-even win rate is exact. Your estimate of the true probability is not, and everything downstream of it inherits that error. A 2-point overestimate of your own win rate turns a modest positive expectation into a negative one at most prices, and nothing in the arithmetic will warn you, because the arithmetic believes whatever you typed.

Break-even also assumes a fixed price. If you bet at -110 and the market closes at -130, your realised break-even was set at the price you took, but the closing number is the better evidence about whether the bet was priced well. That is what closing line value measures, and it stabilises far faster than win rate does.