How is expected value calculated?

EV = (probability × decimal odds) − 1. A bet at decimal 2.10 with a 50% model probability has EV = (0.5 × 2.10) − 1 = +5% expected return per unit staked. See the glossary entry.

What's the difference between decimal, American, and fractional odds?

Decimal odds (2.10) directly multiply your stake. American odds (+110 / −110) reference $100 stakes — positive means win, negative means stake to win $100. Fractional odds (11/10) are stake-relative. All three encode the same bookmaker price.

Why does my +EV bet keep losing?

Variance. A bet with +5% edge wins 5% of the time per dollar staked *on average over many bets*. A single bet still wins or loses based on actual outcome. CLV is the cleaner short-term signal — see the CLV glossary entry.

Calculator

EV from Odds.

Enter odds in any format. Get the implied probability, your edge, and the expected value of the bet at any stake.

Inputs

Odds format

Odds

Your model probability (0–1)

Optional — leave at 0 to skip EV computation.

Stake (USD)

Conversion

Decimal

2.10

American

+110

Fractional

11/10

Implied probability

47.62%

If the line were truly fair (no vig), the book implies this is the chance

Edge

2.38%

(model prob − implied prob) / implied prob

Expected value

$5.00

Per $100 staked, long-run

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Frequently asked questions

How is expected value calculated?

EV = (probability × decimal odds) − 1. A bet at decimal 2.10 with a 50% model probability has EV = (0.5 × 2.10) − 1 = +5% expected return per unit staked. See the glossary entry.
What's the difference between decimal, American, and fractional odds?

Decimal odds (2.10) directly multiply your stake. American odds (+110 / −110) reference $100 stakes — positive means win, negative means stake to win $100. Fractional odds (11/10) are stake-relative. All three encode the same bookmaker price.
Why does my +EV bet keep losing?

Variance. A bet with +5% edge wins 5% of the time per dollar staked *on average over many bets*. A single bet still wins or loses based on actual outcome. CLV is the cleaner short-term signal — see the CLV glossary entry.