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Expected value (+EV) calculator

Enter the odds offered and your fair probability (or fair no-vig odds) to see expected value per unit, edge over the break-even probability and expected profit on a stake.

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Last updated: · Written and reviewed by Ken Lin

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Quick answer

Enter the odds on offer and your fair probability (or fair, no-vig odds). The calculator returns Expected value per unit staked using EV = fair probability × odds − 1, the same formula Odds-API.io's value-bets guide uses [1]. At 2.10 with a 50% fair probability, EV is +5%.

Calculator

Decimal (2.50), American (+150 / −200) or fractional (3/2); comma or dot decimals both work.
Your own estimate of the true chance, e.g. 55.
Leave the probability empty to use fair (no-vig) odds instead.

Positive expected value at your probability.

Expected value (per unit)5.00%
Fair odds2.000
Break-even probability47.62%
Edge (your p − implied p)2.38%
Expected profit on stake5.00

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How it works, with an example

Expected value is the average result per unit if the same price could be taken many times. It is positive only when your probability is above the break-even probability, 1 / odds. Example: offered 3.20, fair probability 34% → EV = 0.34 × 3.20 − 1 = +8.8%; break-even 31.25%; edge 2.75 points. A common way to estimate the fair probability is to de-vig a sharp bookmaker's prices with the Implied probability & no-vig calculator [2].

Formula

EV (per unit staked) = fair probability × decimal odds − 1
break-even probability = 1 / decimal odds
expected profit = EV × stake

Feed it live odds

Finding +EV prices by hand is slow. Odds-API.io Partner link's value-bets endpoint scans bookmakers against a sharp-book fair line and returns each price's EV [1]; you can check its numbers with this calculator.

Partner link — we may earn a commission. See our affiliate disclosure.

Frequently asked questions

Does +EV mean I will win?

No. EV is a long-run average; any single result can lose. It is also only as accurate as the fair probability you enter.

Where does the fair probability come from?

Your own model, or the no-vig price of sharp bookmakers or liquid exchanges. Use the vig calculator to strip the margin first.

How do I check my estimates are good?

Track closing line value and calibration over many forecasts; consistently beating the closing price is a common sign that estimates are sound.

About this guide

Pred-Data publishes independent, source-linked explainers about prediction markets and the AI tools used around them. Every factual claim on this page links to a primary or reputable secondary source, checked on the date shown above. We do not run a trading venue, take bets, or give personal advice.

Author: Ken Lin · Corrections: if you spot an error, we review it and date-stamp the fix.

Affiliate disclosure

Some links on this site (marked “Partner link”) may be affiliate links: if you sign up through them we may earn a commission at no extra cost to you. Partner links use rel="sponsored nofollow" and never change our assessment. Platform links in our comparison tables are plain, non-affiliate links to official sites.

Sources

  1. Value Bets guide (EV formula, response format, limitations) — Odds-API.io docs, accessed 2 Nov 2026
  2. What Is Value Betting? Definition & How to Find Value — Odds-API.io glossary, accessed 2 Nov 2026