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Bookmaker Margin Calculator

See exactly how much margin a bookmaker has built into their odds.

How it is calculated

Each decimal price implies a probability of 1 ÷ odds. The tool adds these for the outcomes you enter: sum = 1/home + 1/draw + 1/away. Leave the draw empty for a two-way market and only home and away are summed. The margin (overround) is (sum − 1) × 100 in percent. The payout ratio is 100 ÷ sum, which is the share of stakes returned if bets were spread across all outcomes. Every odds value must be above 1.00; otherwise there is no result. The tool gives these two figures only. It does not show margin-free odds. It does not check that the outcomes cover the whole market, so a missing outcome gives a misleadingly low or even negative margin.

Worked example

A football match is priced 2.10 home, 3.40 draw and 3.60 away. Implied probabilities: 1 ÷ 2.10 = 0.4762, 1 ÷ 3.40 = 0.2941 and 1 ÷ 3.60 = 0.2778. Their sum is 1.0481. The overround is 1.0481 − 1 = 0.0481, shown as 4.81%. The payout ratio is 100 ÷ 1.0481 = 95.41%. The tool displays a margin of 4.81% and a payout ratio of 95.41%.

Try this example →

Common mistakes

  • Leaving out the draw on a football 1X2 market. With only 2.10 and 3.60 the tool reports a margin of −24.60%, because the missing outcome removes about a quarter of the probability.
  • Adding the draw to a market that has only two outcomes, such as tennis. A made-up third price distorts the margin.
  • Entering odds from different bookmakers and reading the result as one bookmaker's margin. The figure only describes the set of prices you typed in.
  • Typing fractional or American odds. Only decimal odds work, and values of 1.00 or below return no result.
  • Reading the margin as the bookmaker's profit. It is the built-in edge on a balanced book, and the actual profit depends on how the stakes are spread.

About this calculator

Every set of decimal betting odds implies a probability, simply 1 divided by the odds, and if a market were perfectly fair, the implied probabilities of all outcomes would sum to exactly 100%. Bookmakers instead price markets so those implied probabilities sum to more than 100%; the excess is the overround, or bookmaker margin, and it is how bookmakers guarantee themselves an edge regardless of the actual result.

Bettors and odds comparison sites calculate the overround to see which bookmaker is offering the tightest, most favorable, margin on a given match, and professional and arbitrage bettors use it to spot mispriced markets where the true, margin-free odds diverge enough from a bookmaker's posted price to represent value.

Enter the decimal odds for each outcome in a two-way or three-way market and this calculator sums the implied probabilities to show the overround percentage along with the payout ratio. It does not output fair, margin-free odds.

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