How combined probability works
When you have two events, A and B, you often want to know the chance that both happen, or the chance that at least one of them happens. The correct formula depends on whether the events can occur at the same time.
How this calculator works
For independent events (the outcome of one doesn’t affect the other, like two separate coin flips), the probability both happen is P(A) x P(B), and the probability that either happens is P(A) + P(B) – P(A) x P(B).
For mutually exclusive events (they can never both happen at once, like rolling a 2 or a 5 on a single die), the probability both happen is 0, and the probability either happens is simply P(A) + P(B).
Enter each event’s probability as a percentage between 0 and 100. This tool is intended for general educational purposes.
Last reviewed August 2026