How do I combine two independent events?

For independent events, P(A and B) is P(A) times P(B). P(A or B) is P(A) plus P(B) minus P(A and B), which avoids double-counting the overlap.

What does the Bayes mode calculate?

It computes the posterior P(A given B) from the likelihood P(B given A), the prior P(A) and the false-positive rate P(B given not A), using Bayes theorem. This is the classic test-accuracy calculation.

Are my inputs stored?

No. All probabilities are processed in your browser and nothing is transmitted.

Probability Calculator

Complement, AND/OR for independent events, and Bayes.

Probability calculator

Three calculations in one tool: the complement of an event (1 − P), the combined probability of two independent events using AND (P(A)·P(B)) and OR (P(A)+P(B)−P(A)·P(B)), and Bayes’ theorem for a conditional probability P(A|B).

Enter probabilities as decimals between 0 and 1 — everything runs locally in your browser.