A worked example
Decimal 2.50 = fractional 3/2 = American +150, an implied probability of 40%. Decimal 1.50 = fractional 1/2 = American −200, an implied probability of 66.7%.
How the calculation works
Implied probability = 1 / decimal odds. Fractional a/b equals decimal 1 + a/b. American: for decimal odds of 2.00 or more, +100 × (decimal − 1); below 2.00, −100 / (decimal − 1). The implied probability is also the win rate needed to break even at those odds.
What this result does not tell you
An implied probability includes the bookmaker's margin: across the three outcomes of a match the implied probabilities add up to more than 100%. To get fair probabilities, remove the margin with the no-vig calculator.
Common questions
How do I convert American odds to decimal?
For positive American odds, decimal = 1 + odds / 100, so +150 = 2.50. For negative odds, decimal = 1 + 100 / |odds|, so −200 = 1.50.
What does an implied probability of 40% mean?
That the odds would be fair if the outcome happened 40% of the time. Bookmakers add a margin, so the fair probability, after removing the margin, is a little lower.
Is the implied probability the same as the chance of winning?
No. It is what the price implies, margin included. Whether it matches the real chance is exactly what fair odds and closing line value measure.
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