Probability to odds calculator
A 20% chance equals odds of 1 : 4 in favour and 4 : 1 against. Enter the probability to get both forms.
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How to use it
- Enter probability.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Odds in favour = p : (100 - p), simplified; odds against = (100 - p) : p. Odds ratio = p ÷ (100 - p).
Example
Inputs: Probability = 20 %. Result: Odds in favour: 1 : 4; Odds against: 4 : 1; Odds ratio: 0.25.
Limits and caveats
- When the odds do not simplify to small whole numbers they are shown as 1 : x rounded to 4 decimals.
Questions about this tool
What are the odds of a 50% event?
1 : 1, the event is as likely to happen as not.
Why are 0% and 100% not accepted?
The odds would need a division by zero: an impossible or certain event has no finite odds.
What is the odds ratio shown?
The odds in favour as one number, so 75% gives 75 ÷ 25 = 3.