Odds to probability calculator
Convert odds in favour, odds against and decimal odds to probability. See percentages and the difference between these formats.
How to use this page
- Load an example or enter your own data.
- Choose the calculation type and units where available.
- Read the result, additional measures and substituted formula.
What this page does not do: Components a and b must be nonnegative and cannot both be zero. Decimal odds must be at least 1. The result converts notation; it is not a forecast or a betting recommendation.
Further reading
Formula
p = a/(a+b); p = b/(a+b); p = 1/d Odds in favour of 1:4 mean one favourable part to four unfavourable parts: p = 1/(1+4) = 20%. Odds against of 1:4 reverse the interpretation: p = 4/(1+4) = 80%. Neither means “1 in 4”, which is 25%.
Decimal odds of 2.5 imply 1/2.5 = 40%. A quoted price is not evidence of the true probability and may include a margin. This tool does not remove margin; that would require prices for every mutually exclusive outcome.
Frequently asked questions
How can I check the example?
Odds in favour 1:4 give 20%; decimal odds 2.5 give 40%.
What should I check before interpreting the result?
Components a and b must be nonnegative and cannot both be zero. Decimal odds must be at least 1. The result converts notation; it is not a forecast or a betting recommendation.
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