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Bayes' Theorem Calculator

Compute the posterior probability P(A|B) using Bayes' theorem. Use it when you want to update a prior belief about event A after observing new evidence B — common in medical testing, spam filtering, and risk analysis.

Prior Probability P(A)

P(B|A) - Likelihood

P(B) - Evidence

Fill in the required fields to see your result.

Probability

Bayes' Theorem Calculator

Compute the posterior probability P(A|B) from a prior belief, a likelihood, and a false-positive rate. Use it for medical testing, spam filtering, or any scenario where you update beliefs with new evidence.

Prior Probability P(A)

Likelihood P(B|A)

Likelihood P(B|¬A)

Fill in the required fields to see your result.

Key differences

	Bayes' Theorem Calculator	Bayes' Theorem Calculator
Category	Probability	Probability
Inputs required	3	3
Result	P(A\|B) Posterior Probability	Posterior Probability P(A\|B)
What it does	Compute the posterior probability P(A\|B) using Bayes' theorem. Use it when you want to update a prior belief about event A after observing new evidence B — common in medical testing, spam filtering, and risk analysis.	Compute the posterior probability P(A\|B) from a prior belief, a likelihood, and a false-positive rate. Use it for medical testing, spam filtering, or any scenario where you update beliefs with new evidence.