Expected Value (EV) Calculator Explained | OddsGuard
Calculate expected value and percentage edge from stake, odds, and fair probability.
By OddsGuard Editorial · Published
Short answer
A bet has positive expected value (+EV) when the payout odds exceed what the true chance of winning justifies. Over many bets, +EV wagers are expected to make money even though any single bet can lose.
The formula
EV = (win probability x profit if it wins) - (loss probability x stake).
Worked example
Suppose a team at +120 wins 48% of the time. On a $100 bet:
- Win contribution: 48% x $120 = $57.60.
- Loss contribution: 52% x $100 = $52.00.
- EV = $57.60 - $52.00 = +$5.60 per $100 bet (a +5.6% edge).
Why price changes everything
At +105, the exact same 48% win probability produces an EV of -$1.60 per $100 bet (48% x $105 - 52% x $100 = $50.40 - $52.00): the pick did not change at all, yet the weaker price turned a profitable bet into a losing one.
Where true win probability comes from
Most +EV bettors do not guess probabilities from scratch. They take a sharp book's two-way line, strip the vig to find the fair probability, and look for another sportsbook offering a higher payout than that fair price.
Sizing +EV bets
The Kelly Criterion Calculator suggests a stake proportional to your edge and odds. In the +120 / 48% example above, full Kelly is 4.67% of bankroll; many bettors use half-Kelly to smooth out variance.
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