Bayes' Theorem Calculator

Calculate P(A|B) step by step

P(A|B) = P(B|A) × P(A) P(B)

1 Prior Probability

P(A) — Probability that A is true (before considering B)

Example: What's the base rate of having a disease?

P(B|A) — Probability of B, given A is true

Example: Probability of positive test if you have the disease

P(B|¬A) — Probability of B, given A is false

Example: Probability of positive test if you don't have the disease (false positive rate)

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

P(¬A) = 1 - P(A) —

P(B|A) × P(A) —

P(B|¬A) × P(¬A) —

P(B) = —

P(A|B) — Probability of A given B

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