Every set of odds implies a probability. Comparing that number with your own estimate of the true chance is the core idea behind expected value (EV).
Implied probability formulas
- Decimal odds: 1 / decimal. Odds of 2.50 imply 40%.
- Negative American odds: |odds| / (|odds| + 100). Odds of -150 imply 60%.
- Positive American odds: 100 / (odds + 100). Odds of +200 imply 33.3%.
Expected value
EV = (probability of winning x profit) – (probability of losing x stake).
Example: a 100 stake at +150 pays 150 profit. If you believe the true chance of winning is 45%, EV = 0.45 x 150 – 0.55 x 100 = 67.50 – 55 = +12.50 per bet on average. If the true chance is only 35%, EV = 0.35 x 150 – 0.65 x 100 = -12.50.
The catch
EV is only as good as your probability estimate, and a positive EV does not guarantee a win on any single bet. It describes the average result over many bets. Sportsbook prices also include a margin; see how to compare odds across sportsbooks.
Educational content only, not betting advice. Please gamble responsibly; 21+ where applicable.
