- Event probability
- 18.1818 %
- Complement probability
- 81.8182 %
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Enter odds for the event
Odds for an event of 2 to 9 mean a favourable weight of 2 and an unfavourable weight of 9. The total weight is 11, not 9. The event probability is 2/11, approximately 18.1818%, and the complement probability is 9/11, approximately 81.8182%. The default weights illustrate the conversion; they are not a forecast.
Reverse the weights for an odds-against quote
If the quotation is 9 to 1 against an event, enter favourable weight 1 and unfavourable weight 9. Its event probability is 10%. Keep the event label and the direction of the quotation explicit before entering the numbers.
Check the same ratio at a different scale
Weights 20 and 90 produce the same probabilities as 2 and 9 because both weights were multiplied by ten. A zero favourable weight gives event probability zero; a zero unfavourable weight gives event probability one. Both weights cannot be zero because there is then no positive total to normalize.
Separate conversion from evidence
This calculator converts a supplied ratio. It does not establish whether that ratio is a reliable estimate of a default, rate change or other event. Assess the source and assumptions behind an estimate separately from its arithmetic representation.