Expected Value Bet Calculator

Frequently Asked Questions

How is expected value (EV) calculated?

EV = (win probability × profit if win) − (loss probability × stake). With a true 55% chance at +100 odds on $100: 0.55 × 100 − 0.45 × 100 = +$10 EV. Shown for educational analysis only.

What does EV% mean?

EV% = EV ÷ stake × 100. A +$10 EV on a $100 bet is +10% EV. Positive EV means the bet is mathematically favorable given your probability estimate; negative means unfavorable long term.

How reliable is an EV calculation?

Only as reliable as your true-probability estimate. Bookmaker prices already embed a margin, so consistently finding genuinely positive-EV bets is very difficult. Treat results as a study tool, not a profit promise.

Why can a bet have positive EV but still lose?

EV is a long-run average; any single bet can lose due to variance. Even repeated positive-EV wagers swing widely, and most bettors face negative EV overall. Gamble responsibly and within limits.

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This calculator is for informational and educational purposes only and is not betting, gambling, or financial advice. It does not predict outcomes or guarantee returns. Gambling involves risk; never wager more than you can afford to lose. You are responsible for complying with the gambling laws in your jurisdiction.

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How This Calculator Works

This calculator is for informational and educational purposes only and is not betting advice - please gamble responsibly. Expected value (EV) is the average profit or loss per bet if the same wager were repeated infinitely at your estimated true win probability. It is the single most important concept in disciplined betting: a wager is only worth making, in the long run, when its EV is positive, meaning your honest probability is higher than the probability the price implies. Everything else - bankroll management, staking plans, line shopping - is secondary machinery that only matters once you are reliably finding positive−EV bets in the first place; without an edge, perfect bankroll discipline merely slows the rate at which the vig grinds you down. The tool compares your estimated win chance with the book's implied probability (which already includes the vig) and reports EV in dollars, as a percentage of stake, per 100 staked, and the edge in percentage points, so you can see not just whether a bet is +EV but how large that edge is relative to the variance you take on to capture it.

Formula / Method

Convert odds to decimal D. Profit if the bet wins = stake × (D − 1); loss if it loses = stake. With your true win probability p, EV = p × stake × (D − 1) − (1 − p) × stake. EV% = EV ÷ stake × 100. The book's implied probability = 100 ÷ D %; your edge = (p × 100) − implied %. A positive edge produces positive EV. Because the implied figure contains the bookmaker margin, you need a genuine, well−calibrated probability estimate - not a hunch - for the EV number to mean anything.

Worked Example

Odds +120 (decimal 2.20), your true win estimate 50%, stake 100. Profit if win = 100 × 1.20 = 120; loss if lose = 100. EV = 0.50 × 120 − 0.50 × 100 = 60 − 50 = +10. EV% = +10%, EV per 100 = +10. The book's implied probability = 100 ÷ 2.20 ≈ 45.5%, so your edge = 50 − 45.5 = +4.5 percentage points - a positive−EV bet if your 50% estimate is accurate. If your true estimate were only 44%, EV = 0.44 × 120 − 0.56 × 100 = 52.8 − 56 = −3.2, a losing proposition.

Common Mistakes

Using the book's implied probability as your "true" estimate - that guarantees EV near zero or negative after vig.

Overconfidence in subjective probabilities; small estimation errors flip the sign of EV.

Confusing a positive EV per bet with a guaranteed win - variance can be brutal over small samples.

Forgetting that EV assumes your probability is correct; it is only as good as that input.

Ignoring that beating the implied number still leaves long−run risk and limits in the real market.

Tips & FAQ

Where do I get a true probability? From models, no−vig consensus lines, or sharp−book prices - never from the same book you are betting, because doing so just hands you back the implied number plus its margin and guarantees a non−positive edge. Is +EV enough? It is necessary but not sufficient; bankroll management, realistic calibrated estimates, and the discipline to keep betting through inevitable downswings matter as much as the sign of the EV. Why per 100? It standardizes comparisons across stake sizes so two bets of different sizes can be ranked on equal footing. How big a sample do I need? Far more than intuition suggests - hundreds of bets before the long−run average reliably dominates variance, which is why a few winning weeks prove nothing about an edge. Remember EV is a long−run average over many independent bets; any single result can swing far from it, the house edge is built into prices, and most bettors meaningfully overestimate their own probabilities. Treat betting as entertainment with a fixed budget, set limits in advance, never chase losses, and seek help if it stops being fun.

Expected Value Bet Calculator

Frequently Asked Questions

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