Bookmaker Margin Explained: How to Calculate the Overround

What information do you need?

You need prices for the same market at the same time, with outcomes that do not overlap and cover every case in the example. For an over/under 2.5-goals market on a completed match, that means both the over and under prices.

A 1X2 market needs three prices: first-team win, draw and second-team win. Do not mix a first-half price with a full-match price, or prices captured at different times, and label the sum the margin of a single market.

Example: over 2.5 at 2.37 and under 2.5 at 1.65

This is a mathematical example from the channel lesson, not a current price quotation:

(100 ÷ 2.37) + (100 ÷ 1.65) − 100 ≈ 2.80 percentage points

The implied probabilities total approximately 102.80%. The excess above 100% is the overround, commonly referred to as the quoted market margin. Keep full precision during calculation and round the final result.

Why does 2.80% not mean guaranteed bookmaker profit?

The figure describes pricing. Actual profit depends on the distribution of stakes, outcomes and liabilities; adding implied probabilities alone does not reveal it. Nor does it establish that every customer will lose the same percentage.

For mathematical illustration only, in a balanced-book model where stakes are arranged to make the payout liability equal for every outcome, the share retained from total stakes is 1 − 1 ÷ 1.0280015 ≈ 2.724%. Its difference from 2.80 percentage points shows why the meaning of “margin” needs to be specified.

Why can’t you add 1X, X2 and 12 in the same way?

Double-chance outcomes overlap. A draw satisfies both 1X and X2; a first-team win satisfies both 1X and 12. They are not three mutually exclusive outcomes. Adding their implied probabilities and subtracting 100% does not give a valid overround using the ordinary 1X2 method.

Markets with refunds or partial settlements also require treatment of their possible returns rather than copying the over/under 2.5 example without adjustment.

How should you interpret the result?

When comparing equivalent markets, a smaller overround describes a lower aggregate pricing margin. It does not prove that a particular selection offers value. The margin may be distributed differently across outcomes, and the true probabilities remain uncertain.

When comparing prices from 1xBet or another operator, retain the capture time and market scope, and keep the arithmetic separate from a match prediction. Read expected value explained for the distinction between price and estimated probability.

Can removing the margin reveal the true probabilities?

Dividing each implied probability by their sum produces percentages totalling 100%, but assumes a particular distribution of the margin. It is a mathematical normalisation, not a guaranteed discovery of the true probabilities.