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Conditional Probability P(A | B) Calculator

P(A | B) = P(A ∩ B) / P(B).

Compute the conditional probability P(A | B) from the joint probability P(A ∩ B) and the marginal P(B). Reports P(B | A) by Bayes' rule when both marginals are supplied.

Daniel Oh By Daniel Oh
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

P(A | B) = P(A ∩ B) / P(B); Bayes: P(B | A) = P(A ∩ B) / P(A).

In depth

Compute the conditional probability P(A | B) from the joint probability P(A ∩ B) and the marginal P(B). Reports P(B | A) by Bayes' rule when both marginals are supplied.