Enter decimal odds to calculate their implied probability. Or enter a percentage to convert probability to fair odds without margin. Fractional and American equivalents are shown too.
Short answer
The implied probability of decimal odds is 1 / odds: 2.50 corresponds to 40.00%, fractional 3/2 and American +150. In reverse, the margin-free fair odds of a probability are 1 / probability. A single price includes margin, so it does not give the true probability of the outcome.
Odds → probability
LOCAL CALCULATION
RESULT
Implied probability—
Fractional odds—
American odds—
Enter decimal odds greater than 1.00. Implied probability includes the market margin.
Probability → fair odds
LOCAL CALCULATION
RESULT
Fair odds (no margin)—
Fractional odds—
American odds—
Enter a percentage between 0 and 100. Fair odds are shown with at least two and at most four decimals; the fractional odds are calculated exactly from the percentage you typed.
Method and examples
For decimal odds of 1.50, 2.50 and 4.00, the implied probabilities are 66.67%, 40.00% and 25.00%. These are figures implied by a single price, not a prediction; the market margin is still included. Compare all three prices in a 1X2 market.
Implied probability = 100 / odds. Fair odds = 100 / probability. Fractional = odds − 1, or (100 − probability) / probability, as a reduced fraction. American: +(odds − 1) × 100 if the odds are 2.00 or more, otherwise −100 / (odds − 1).
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Implied probability = 100 / odds. For example, odds of 2.50 imply 40.00% and odds of 1.85 imply 54.05%. This figure includes the market margin.
What are fair odds? +
Fair odds carry no margin and are simply the inverse of the probability: fair odds = 100 / probability. A 40% probability gives fair odds of 2.50; a 55% probability gives 1.8182 (fractional 9/11).
How are fractional and American odds calculated? +
Fractional odds are the decimal odds minus 1: 2.50 → 3/2. For American odds, use +(odds − 1) × 100 when the decimal odds are 2.00 or more (2.50 → +150), and −100 / (odds − 1) below that (1.80 → −125).
Is implied probability the true probability? +
No. Prices include a margin, so the probabilities across a market add up to more than 100%, and a single price does not give the true probability of the outcome. Use the 1X2 probability and margin tool to see the margin.
Last updated: 4 November 2026 · Responsible: Cortenscore editorial team · Spotted an error? Report a correction. This page is for statistics education; it is not a prediction or betting advice.
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