What bookmaker margin is and how to find fair odds
Updated 13 Nov 2026 · 3 min read
Every betting market is priced so that the bookmaker earns on average, whatever the result. That built-in cut is the margin. It is never printed next to the prices, but two minutes of arithmetic bring it out.
Where the margin sits in a set of prices
Turn each price into an implied chance: one divided by the decimal price. In a market with no cut, the chances of all outcomes would add up to exactly 100%. They never do. The amount above 100% is the margin.
Prices in another format go through the odds format converter first. Reading decimal, fractional and American odds explains the three formats.
A two-way market worked through
Both sides of a market are priced 1.91. Each implies 52.36%. Together that is 104.71%, so the margin is 4.71%.
Scale the two chances back down so that they add up to 100% and each side is an even chance. The fair price is 2.00. You are offered 1.91 instead.
Three outcomes follow the same steps
A match with a draw has three prices, say 2.10, 3.40 and 3.60. The implied chances add up to 104.81%, a margin of 4.81%. With the margin removed, the first outcome has a chance of 45.43% and a fair price of 2.20.
The margin calculator takes two or three prices and lists the fair price of each outcome.
What the margin costs over time
A book of 104.71% pays back 95.50% of the money staked, on average and across all outcomes. Out of every 100 staked, about 4.50 stays with the bookmaker.
This is the house edge under another name. A crash game at an RTP of 97% keeps 3% of every stake, and what RTP means in crash games covers that side. The expected loss calculator turns either figure into an amount for a given turnover.
Fair odds are an estimate, not a fact
Removing the margin in proportion assumes the bookmaker loaded every outcome equally. Often outsiders carry more of it than favourites, so the fair price of a long shot is usually a little shorter than this method says.
When the best prices from different bookmakers bring the total under 100%, the margin has turned negative. That is an arbitrage, and the arbitrage calculator shows the stakes.
Questions about margin and fair odds
How do I find the margin of a market?
Add up one divided by each decimal price, for every outcome of the market, and subtract one. Two sides at 1.91 give 4.71%.
What is a fair price?
The price an outcome would have with the margin taken out. For two equal sides offered at 1.91 it is 2.00.
Is a margin under 5% good?
It is on the low side for most sports markets, but what counts is the comparison: the same event can carry very different margins from one bookmaker to the next.
Does the margin work like RTP?
Yes. The payout rate of a market, 95.50% in the example, plays the part of the RTP of a casino game, and the margin plays the part of the house edge.
Tools that measure a margin
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