Enter the bookmaker's odds and your own estimated probability to see whether a bet has positive or negative expected value — and how much edge you have per unit staked.
Expected value (EV) is the average outcome of a bet if you placed it an infinite number of times. A bet with +EV will profit over a large sample; a bet with -EV will lose. The formula is:
EV = (Your Probability × Profit per unit) − (1 − Your Probability)
Example: odds of 2.50 (+150 American), and you estimate the true probability at 45%:
That means for every £100 staked, you expect to profit £12.50 on average over a large sample.
The break-even probability is the win rate required to produce zero EV at the given odds: break-even = 1 ÷ odds. If your estimated probability exceeds the break-even percentage, the bet is +EV. If it falls below, the bet is -EV.
Use the No-Vig calculator to find the fair probability stripped of bookmaker margin — that is a better benchmark than the raw implied probability for estimating break-even.