About the Conditional Probability Calculator
Compute P(A|B) from P(A and B) and P(B), or use Bayes’ theorem with P(B|A), P(A) and P(B).
Also known as: bayes theorem calculator, p(a given b), bayes rule, conditional probability formula.
How to use this calculator
- Enter method, p(b) and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
P(A|B) = P(A∩B)/P(B) = P(B|A)·P(A)/P(B)
Worked example
Using the values pre-filled in the calculator above:
- Method: Bayes' theorem
- P(B|A) = 0.9
- P(A) = 0.01
- P(B) = 0.3
the calculator returns:
- P(A|B): 0.03
- As a percentage: 3%
- Odds (1 in …): 1 in 33.3333