Probability Calculator
Calculate probabilities for single and combined events.
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Frequently asked questions
For equally likely outcomes, divide the number of favorable outcomes by the total number of outcomes. Rolling a 4 on a fair six-sided die is 1 favorable outcome out of 6, so the probability is 1/6, or about 16.67%.
Independent events don't affect each other, so both can happen: P(A and B) = P(A) × P(B). Mutually exclusive events can't happen together, so P(A and B) = 0 and P(A or B) = P(A) + P(B). Pick the option that matches your scenario before reading the combined results.
For independent events, P(A or B) = P(A) + P(B) − P(A) × P(B), which subtracts the overlap so it isn't double-counted. P(neither) is just 1 − P(A or B). The calculator also shows P(exactly one), the chance that one event happens but not the other.
No. Every calculation runs in your browser with JavaScript. The numbers you type stay on this page and are never uploaded to a server.
Last updated 2026-06-23.