Expected Value (EV) Calculator

Expected value is the single most important betting concept

Expected value (EV) is the average result you’d get from placing the exact same bet an enormous number of times, given the odds on offer and your own honest estimate of the true win probability. It’s the concept underneath almost every other tool on this page — Kelly staking, arbitrage, no-vig odds, and bonus expected loss are all applications of the same idea: that a bet’s worth isn’t determined by whether it wins or loses this one time, but by what it would average out to across many repetitions of the same decision. A bettor who consistently makes +EV decisions will, over a large enough sample, come out ahead — even though any individual bet remains genuinely uncertain.

The formula and a worked example

EV = (P(win) × amount won) − (P(lose) × stake), where amount won is your stake multiplied by (decimal odds − 1) — your net profit if the bet lands. Suppose you stake €100 on a bet at decimal odds of 2.20, and you genuinely believe the true win probability is 50% (higher than the bookmaker’s implied 45.5%, meaning you think this is a value bet). Amount won if it lands: €100 × (2.20 − 1) = €120. EV = (0.50 × €120) − (0.50 × €100) = €60 − €50 = +€10. On average, across many bets placed under these exact conditions, you’d expect to profit €10 per €100 staked — a genuinely positive-EV proposition, assuming your 50% probability estimate is accurate.

Break-even probability as a sanity check

Every set of odds implies a break-even probability — the win rate at which the bet would have exactly zero expected value, neither +EV nor -EV. It’s simply 1 ÷ decimal odds, which is also the bookmaker’s own implied probability for that price. Comparing your own estimated probability to this break-even figure is the fastest sanity check available: if your estimate is higher than break-even, you believe the bet is +EV; if lower, you believe it’s -EV. In the example above, decimal odds of 2.20 imply a break-even probability of about 45.5% — your 50% estimate sits above that line, which is exactly why the bet came out positive.

The honest limitation: your probability estimate

This calculator performs the EV arithmetic exactly and reliably — but the entire result rests on the accuracy of the probability you enter, and that number always comes from you, not from the tool. Overestimating your own edge is the single most common way bettors convince themselves a bet is +EV when it isn’t; there’s no formula that can correct for a probability estimate that was too optimistic to begin with. Treating this tool’s output with appropriate skepticism — and being deliberately conservative about your own probability estimates — is at least as important as the calculation itself.

How EV connects to the rest of your betting math

Once you can calculate a single bet’s expected value, several other useful questions follow naturally from it. The Kelly Criterion takes a +EV bet's edge and works out how large a stake maximizes long-run bankroll growth, rather than just confirming the bet is worth taking at all. Comparing a de-vigged, fair probability (from our No-Vig Odds Calculator) against your own probability estimate is one systematic way to arrive at the probability this tool needs as an input, rather than guessing at it in isolation. And running the same EV math across every leg of a parlay is exactly how a bettor can tell whether a combined multi-leg bet is genuinely worth its compounded risk, rather than just looking appealing because of its large potential payout.

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