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MARGIN CALCULATOR

Bookmaker margin calculator

The odds of every outcome of one market at one bookmaker. You get: the margin as a percentage, the implied probability of each outcome and the fair odds without the margin. Runs in your browser, no sign-up.

Outcomes

Σ 1/k = 1.0534

Margin 5.34 %

OutcomeOddsImpliedFairFair odds
11.8554.05 %51.32 %1.949
21.9551.28 %48.68 %2.054

Margin = Σ 1/k − 1. Fair probabilities use the proportional method.

How to use the calculator

  1. Choose the number of outcomes in the market: 2 (match winner, total, handicap) or 3 (win, draw, loss).
  2. Enter the odds of every outcome from one bookmaker and one market.
  3. Read the margin and the table: the implied probability is built into the odds together with the margin; the fair one is what is left after the margin is removed.
  4. Compare the fair odds with another bookmaker’s price: if theirs is higher, by the first bookmaker’s estimate it is a value bet. The estimate is most reliable from a low-margin bookmaker.

How the margin is calculated

The margin equals the sum of the inverse odds of all outcomes minus one: margin = Σ 1/K − 1 = 1/k₁ + 1/k₂ (+ 1/k₃) − 1. The implied probability of an outcome is 1/kᵢ, the fair probability is (1/kᵢ) / Σ 1/K, and the fair odds are kᵢ × Σ 1/K. Two-outcome example: 1.85 and 1.95 → 0.5405 + 0.5128 = 1.0534, margin ≈ 5.3%, fair odds 1.949 and 2.054. Three-outcome example: 2.10, 3.40 and 3.50 → 0.4762 + 0.2941 + 0.2857 = 1.0560, margin ≈ 5.6%. More in the glossary entry “Bookmaker margin”.

What to keep in mind

  • The margin is calculated for one market at one bookmaker. Odds from different bookmakers in one row give not a margin but the sum used to look for a surebet.
  • Fair odds here use the proportional method: the margin is removed from each outcome in equal shares. Bookmakers usually load more margin onto clear underdogs, and other methods (Shin, power) give them slightly higher odds.
  • Σ 1/K below one means a negative margin. This happens when the odds come from different bookmakers, and it is a surebet: the surebet calculator splits the stakes.

The lower the margin, the closer the odds are to fair and the more often the bookmaker ends up as a leg of a surebet. The Dozor scanner compares the lines of dozens of bookmakers and shows pairs where the combined margin is already negative.

FAQ

How do you calculate a bookmaker’s margin?

Add up the inverse odds of all outcomes of one market and subtract one. Odds of 1.90 and 1.90: 1/1.90 + 1/1.90 = 1.053, a margin of 5.3%.

What are fair odds?

Odds without the bookmaker’s margin: on average a bet at fair odds yields neither profit nor loss. They equal the bookmaker’s odds multiplied by Σ 1/K: 1.85 with a sum of 1.0534 → 1.949.

What margin counts as low?

The lower the margin, the better for the player. Sharp bookmakers such as Pinnacle usually run lower margins than retail ones. On secondary markets and in live betting the margin is usually higher than on the match winner. To check a bookmaker, enter its odds for one market above.

Why can the margin be negative?

At a single bookmaker, only through a pricing error. If the odds come from different bookmakers, a negative margin means a surebet: bets on every outcome make a profit whatever the result.

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