Probability Calculator

How the Probability Calculator Works

This calculator takes the probabilities of two independent events, A and B, and works out the common combinations: both happening, at least one happening, neither happening, and exactly one happening. Independent means one event does not affect the other — like two separate coin flips or dice rolls.

For independent events, the chance of both is the product of their probabilities; the chance of at least one is their sum minus that overlap; and the chance of neither is the product of their complements. Enter each probability as a percentage from 0 to 100.

P(A and B) = P(A) × P(B)   P(A or B) = P(A) + P(B) − P(A and B)