Live Bayes calculator

Pick a scenario or build your own — the posterior updates instantly.

Posterior — what the evidence actually means
The formula working live

  

What each part means

Posterior P(A|B) What you believe AFTER seeing the evidence. This is what you want to find.
Likelihood P(B|A) How often does this evidence appear when A is actually true?
Prior P(A) Your base belief BEFORE seeing any evidence. How common is A in general?
False alarm rate How often does the evidence appear even when A is NOT true? (P(B|not-A))