Odds calculator converts between probability and odds in both directions.
About this calculator
Odds calculator converts between probability and odds in both directions. Enter decimal odds like 3 (meaning 3:1 in favor) or type 3:1 directly — the implied probability is 75%. Switch modes to start from a percentage like 25% and get decimal odds 0.333 (1:3 in favor).
Sports books and poker players think in odds; statisticians and doctors think in probabilities. The formulas link them: odds in favor = p/(1−p), so probability = odds/(1+odds).
A fair coin has 50% probability and 1:1 odds. A 10% chance event has 0.111 decimal odds, written as 1:9 against.
Use [[probability]] for union and intersection rules, [[percentage]] for general percent math, and [[z-score]] when comparing outcomes to a normal distribution.
Common uses
- Convert betting decimal odds to implied win probability
- Translate a medical risk percentage into odds for a patient discussion
- Check whether implied probabilities across outcomes sum to 100%
- Homework problems converting between odds ratios and percentages
- Compare two candidates
Frequently asked questions
What probability do 3:1 odds in favor imply?
3:1 in favor means O = 3. Probability = 3/(3+1) = 0.75 = 75%. You expect three wins for every one loss at fair odds.
What are the odds for a 25% probability?
O = 0.25/(1−0.25) = 0.333, written as 1:3 in favor or 3:1 against. The event happens once in every four trials on average.
What is the difference between odds for and odds against?
Odds for use wins per loss: 3:1 for means three wins per one loss. Odds against flip the ratio: 3:1 against means one win per three losses. They are reciprocals.
Can probability be exactly 0% or 100%?
No for this converter — odds are undefined at 0% and infinite at 100%. Enter values strictly between 0 and 100 when converting probability to odds.