Bookmaker margin calculator
Enter the odds for every outcome in a market — home, draw and away, or both sides of a tennis match — to see how much margin the bookmaker has built in, and what each price would be without it.
What the margin tells you
A fair market's implied chances add up to exactly 100%. Bookmakers price above that — the "overround" — and the excess is their margin. Big football matches often carry only a few percent; obscure markets, player props and bet builders carry far more. The lower the margin, the less each bet costs you over time.
When two bookmakers' prices together add up to less than 100%, you have an arbitrage: backing every outcome locks in a profit. That's exactly what our scanner hunts for. What is arbitrage betting? →
Questions
How do you calculate a bookmaker's margin?
Add up 1 divided by the decimal odds of every outcome. Subtract 1 and multiply by 100. Odds of 2.10, 3.40 and 3.60 give 0.476 + 0.294 + 0.278 = 1.048, a margin of about 4.8%.
What is overround in betting?
The total of a market's implied probabilities. Anything above 100% is the bookmaker's margin: 104.8% means a margin of 4.8%.
More free tools
- Bet builder calculator — Work out the fair odds of any bet builder and see whether your bookmaker's price is value.
- Odds converter — Fractional, decimal, American and implied probability — convert any price instantly.
- Value bet calculator — Compare a bookmaker's price with the fair price and see the edge and expected profit.
- Arbitrage calculator — Two or three outcomes, back or lay: exact stakes for a guaranteed profit.