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Bookmaker Margin Calculator

Work out bookmaker margin instantly with clear inputs, formula shown and shareable results.

About Bookmaker Margin Calculator

The book total is the sum of one over each price; margin is one minus the reciprocal of that total, and fair odds are each price multiplied by the book total. A 5% margin means the market pays back only 95 units per 100 staked over time, which is the hurdle every betting strategy has to clear before it can win.

Formulas

Book total

book = 1 / odds A + 1 / odds B + 1 / odds C

Margin

margin = 1 - 1 / book total

Worked example

With the default values below, Bookmaker Margin Calculator returns Bookmaker margin of 24.577%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Odds on outcome Aminimum 1
1.8
Odds on outcome Bminimum 1
2.1
Odds on outcome C (0 if none)minimum 0
3.4

Results

Bookmaker margin
24.577%
Overround
32.586%
Fair odds on outcome A
2.3866
Payout rate to bettors
75.423%

Step by step

  1. 1Values used
  2. 2Book total
  3. 3Margin
  4. 4Bookmaker margin= 24.577
  5. 5Overround= 32.586
  6. 6Fair odds on outcome A= 2.3866
  7. 7Payout rate to bettors= 75.423

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Bookmaker Margin figure worked out?

book = 1 / odds A + 1 / odds B + 1 / odds C. The book total is the sum of one over each price; margin is one minus the reciprocal of that total, and fair odds are each price multiplied by the book total.

Why does this matter?

A 5% margin means the market pays back only 95 units per 100 staked over time, which is the hurdle every betting strategy has to clear before it can win.

What do I need to enter?

Enter odds on outcome a, odds on outcome b, odds on outcome c (0 if none). The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

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