Calculate event probability, combinations (nCr), and permutations (nPr).
Enter the number of favorable outcomes and total possible outcomes for one or two events, and this calculator returns the probability of each event individually, along with the combined probability of both happening (independent events) or either happening.
Probability of a single event = Favorable Outcomes / Total Outcomes.
Both events happening (independent): multiply the individual probabilities together, P(A) × P(B).
At least one event happening: P(A) + P(B) − P(A and B), which avoids double-counting the overlap between the two events.
Independent events don't affect each other's outcome — the result of one has no bearing on the probability of the other, like two separate coin flips. For independent events, the combined probability is a simple product.
Probability is usually expressed as a number between 0 and 1 (or as a percentage between 0% and 100%). A probability of 0 means the event is impossible; a probability of 1 (100%) means it's certain.
Probability compares favorable outcomes to all outcomes (e.g. 1/6 for rolling a specific number on a die). Odds compare favorable outcomes to unfavorable outcomes (1-to-5 for the same roll). They describe the same likelihood in two different formats.