Probability Calculator
Find the probability of an event from its favourable and total outcomes.
What is Probability?
Probability measures how likely an event is on a scale from 0 (impossible) to 1 (certain): P(A) = favourable outcomes ÷ total outcomes, when every outcome is equally likely. The complement P(not A) is 1 − P(A), which is often the easier calculation.
How it works
The two counts are divided and the result is shown three ways — decimal, percentage and reduced fraction — because a mark scheme may ask for any of them. The odds for and against are derived from the same counts; they are not probabilities, and mixing the two up is the commonest error in the topic.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.