Probability Calculator

For independent events, 'and' multiplies: P(A)×P(B). 'Or' adds but removes the double-counted overlap: P(A)+P(B)−P(A)P(B). Everything here derives from those two rules plus complements (P(not A) = 1 − P(A)).

These formulas require that A doesn't influence B. Rain and umbrella-carrying aren't independent; coin flips are. When events are linked, you need conditional probability — P(A and B) = P(A)×P(B given A) — and the numbers can shift dramatically.