▣ CALCULATORS Updated July 25, 2026
Probability Calculator
Single-event and repeated-trial probability.
Favourable outcomes
Total outcomes
Trials
Result
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How it works
Single-event probability is favourable outcomes divided by total outcomes. The repeated-trial figure uses 1 − (1 − p)^n, the chance of at least one success.
Frequently asked questions
What are odds against?
The ratio of failures to successes, so a 1-in-4 chance is 3:1 against.
What does 'at least once' mean?
The probability that the event happens one or more times over the number of trials you enter.
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