Bayes Theorem Calculator
Enter a prior probability and the likelihood of evidence under each hypothesis; the result uses Bayes’ theorem with explicit inputs.
A QUICK WALKTHROUGH
How to use this tool
- Enter P(H), the prior probability of the hypothesis.
- Enter P(E|H) and P(E|not H), the evidence likelihoods.
- Calculate the posterior and review the assumptions.
Explicit assumptions
The calculator treats H and not H as the only two mutually exclusive, exhaustive hypotheses. It treats E and not E as complementary evidence outcomes and uses only the probabilities you enter.
Bounded probabilities
Every input is a percentage from 0 to 100. The denominator must be positive; rounding is for display only.
GOOD TO KNOW
Common questions
Does it choose a prior for me?
No. Enter the prior probability that matches your context.
What does the second likelihood mean?
It is P(E|not H): the probability of seeing the same evidence when the hypothesis is false.
Can I enter percentages?
Yes. Enter values from 0 to 100; the calculator converts them to probabilities locally.