Bayes' Theorem Calculator

Calculate conditional probability P(A|B) using Bayes' Theorem

P(A) - Prior probability of A (0 to 1):

P(B|A) - Probability of B given A (0 to 1):

P(B|¬A) - Probability of B given not A (0 to 1):

Bayes' Theorem describes the probability of an event based on prior knowledge of conditions related to the event.

Formula: P(A|B) = [P(B|A) × P(A)] / P(B)

Where P(B) = P(B|A) × P(A) + P(B|¬A) × P(¬A)

Example: Medical diagnosis - given a positive test result, what's the probability of having the disease?

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Formula Source: Standard Mathematical References

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ðŸ”„Last reviewed: May 2026

âœ“Formula checks are based on standard references and internal QA review.