🔀 Conditional Probability Calculator
Enter the probability of event A, event B, and both A and B happening together to calculate the conditional probabilities P(A|B) and P(B|A).
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What is Conditional Probability?
Conditional probability measures how likely event A is, given that event B has already happened. It’s written P(A|B) and is used constantly in statistics, risk analysis, and everyday reasoning about uncertain events.
The Formula
P(A|B) = P(A and B) / P(B), and symmetrically P(B|A) = P(A and B) / P(A). If P(A|B) is equal to P(A), the two events are considered statistically independent, meaning knowing B happened doesn’t change the odds of A.
- All probabilities are entered as percentages between 0 and 100.
- If P(B) is 0, P(A|B) is reported as 0 to avoid dividing by zero.
This tool is intended for general educational use, not for professional statistical, legal, or medical decision-making.
Last reviewed August 2026