Expected value (EV) calculator
Is a price worth betting? Compare it with a fair probability, a fair price or the two-sided market with the vig removed, and see the EV, the edge and the Kelly stake with every step of the math.
Inputs
Result
updates as you typeRun this math on every line, automatically
The +EV finder does this for every price at every book, against a fair built from the other books' devigged prices, and drops games at their start time.
How it works
Expected value is the average result of a bet if you could place it many times at the same price and the same true chance. Per $1 staked:
EV = p × d − 1
p = the fair (true) probability of winning · d = the decimal price you get, after any fee
The hard part is p. A sportsbook's own price includes its margin (the vig), so you need a fair probability from somewhere else. The calculator takes it three ways: your own win probability, a fair price you already have, or a two-sided market from a sharp book or exchange, which it devigs with the method you pick. Probit is the default, as in our tools; the no-vig calculator shows all methods side by side.
It also returns the edge (fair probability minus the break-even probability of your price, in percentage points) and the Kelly fraction. If you bet at an exchange or prediction market, pick it under Where you bet and the price is converted to your net price after the venue's published fee first.
Worked example
A book offers +150 on a side. A sharp market prices the same side at +130 and the other side at −155. Which is the better guide to the true chance?
Sharp market implied: 1/2.3000 = 43.48% and 1/1.6452 = 60.78% → booksum 104.26%
Probit devig → fair probability of our side 41.33% (fair odds +141.9)
Your price +150 = decimal 2.5000, break-even 40.00%
EV = 0.4133 × 2.5000 − 1 = +3.34% → $3.34 per $100 on average
Full Kelly = 2.22% of bankroll; quarter Kelly = 0.56%
The price beats the fair line, so the bet is positive EV. Whether it is worth taking still depends on whether the sharp market is current and the book will take your size.
Things to watch
- The fair is the whole game. A wrong fair probability gives a confident, wrong EV. Use a liquid, sharp two-sided market, or several books blended (our tools do this for you).
- Stale prices. A price that has not moved while the market has is the most common fake edge. Check the time on both prices.
- Don't devig the book you bet against itself. Its own two sides only tell you its own opinion, minus vig. The fair has to come from other books.
- Big EV on longshots. +EV of 10% or more on a +600 price is usually a stale or mis-keyed line, not a gift. Confirm before betting.
- Limits. Positive EV on paper only pays if the book takes your bet at that price and size.