Fair odds calculator: remove the bookmaker margin
Fair odds are the odds with the bookmaker margin removed: fair odds = 1 ÷ probability. To get them from a bookmaker's prices, turn each price into a probability (1 ÷ odds), divide each one by the sum of all of them and convert back to odds. Example: 2.10 / 3.40 / 3.60 add up to 104.8%, so the fair home odds are 1 ÷ (47.6% ÷ 104.8%) = 2.20. Work it out with your odds ↓ No sign-up: everything runs in your browser.
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Does the price you are offered have value?
What fair odds are
The odds a bookmaker would pay if it made nothing: the price that matches the probability of the outcome exactly. If something happens 50% of the time, its fair odds are 2.00.
Fair odds = 1 ÷ probability
Why bookmaker odds don't add up to 100%
Turn each price into a probability (1 ÷ odds) and add them up. A 1X2 at 2.10 / 3.40 / 3.60 gives 47.6% + 29.4% + 27.8% = 104.8%. That extra 4.8% is the margin: what the bookmaker keeps on average. The calculator removes it and gives you probabilities that add up to 100%.
Proportional or power
The proportional method spreads the margin in line with each probability. It is the most common and works for nearly everything.
Bookmakers tend to load more margin on the least likely outcome (the favourite-longshot bias). The power method allows for that: it makes the favourite a little shorter and the outsider a little longer. On low-margin markets the two give almost the same answer.
What it is for
Comparing prices. If the fair odds from an efficient market are 2.00 and another bookmaker offers 2.15, that price has value. It is the same thing CLV measures, only before kick-off.
If you want our model's probability instead of the market's, MatchScan calculates it for any match in 31 leagues: analyse a match. How we do it is in the methodology.
Frequently asked questions
How do you calculate fair odds? Turn each price into a probability (1 ÷ odds), divide each one by the total, and turn it back into odds with 1 ÷ probability.
What margin is normal? In the big leagues a 1X2 usually carries 3% to 7%. In smaller leagues and specials it can go above 10%.
Are fair odds the true probability? They are the market's probability with the margin removed. A good estimate, especially in markets with a lot of money, but not absolute truth.
Does betting above fair odds guarantee a profit? No. A price with value makes money on average over many bets, but any single bet can lose.
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