How do you calculate implied probability?

For decimal odds, divide one by the price: 4.00 implies 25%. For fractional odds, divide the denominator by the sum of both numbers, so 6/4 implies 40%. For American odds the method depends on the sign: for a negative price such as -150, divide 150 by 250 to get 60%; for a positive price such as +200, divide 100 by 300 to get 33.3%.

Why do implied probabilities add up to more than 100%?

Every price carries the bookmaker's margin, so the probabilities implied by the odds on all outcomes in a market sum to more than 100%. The excess is the overround. Removing it proportionally produces the fair, or de-vigged, probabilities that betting models are judged against, and that bettors compare with their own estimates.

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Implied Probability

Last reviewed 24 September 2026

What is Implied Probability?

The probability of an outcome implied by its odds. Derived by inverting the price, it is the bridge between a bookmaker quote and a percentage chance.

Key takeaways

Implied probability is the chance of an outcome implied by its odds; for decimal odds it is one divided by the price.
Because every price carries margin, implied probabilities across a market sum to more than 100%, and the excess is the overround.
A bettor who judges the fair chance to be higher than the implied probability after margin has found value.

Why it matters

Implied probability turns a price into something a bettor can reason about. For decimal odds it is one divided by the price, so 4.00 implies 25%. For fractional odds it is the denominator over the sum of both numbers, and for American odds it depends on the sign. The figure is not the bookmaker's true estimate of the chance, because every price carries margin, so implied probabilities across a market always sum to more than 100%.

That gap is the whole commercial point. The excess over 100% is the overround, and removing it proportionally produces the "fair" or de-vigged probabilities that models are judged against. A bettor who believes the fair chance of an outcome is higher than the implied probability after margin has, by definition, found value. This is also how closing lines are used as a benchmark: the market's implied probabilities at kick-off are treated as the most efficient available estimate, which is why beating them consistently is the standard test of a genuine edge.