Implied probability and bookmaker margin explained
How to turn decimal odds into probabilities and remove the bookmaker's margin, with a worked example.
Decimal odds convert to a probability with one division: probability = 1 / odds. Odds of 2.00 mean 50%, 4.00 means 25%.
The margin (overround)
Add up the three 1X2 probabilities and you get more than 100%. The extra is the bookmaker's margin. For 2.10 / 3.40 / 3.50: 1/2.10 = 47.6%, 1/3.40 = 29.4%, 1/3.50 = 28.6%, total 105.6%, so the margin is about 5.6%.
Removing the margin
Divide each probability by the total: 47.6 / 105.6 = 45.1% home, 27.9% draw, 27.1% away. SameOdds shows these fair probabilities next to the real results so you can see whether a price level has historically over- or under-delivered.
Why compare
If teams priced around 45% have actually won 50% of the time over thousands of matches, that price range has been generous. Over a handful of matches the same gap means very little.