How probability calculator works
Probability measures how likely an outcome is, from 0 (impossible) to 1 (certain). This calculator handles three classic scenarios: coin flips (the binomial probability of exactly k heads in n flips), dice rolls (the chance of an exact, at-least, or at-most result on a die), and drawing without replacement (the hypergeometric probability of drawing k successes from a bag of N items containing K successes).
For coins it uses P(k heads in n) = C(n,k) / 2^n, where C(n,k) is the binomial coefficient. For dice it counts the favourable outcomes over the total sides — exactly one for an exact roll, (sides − target + 1) for "at least", and target for "at most". For marbles it uses the hypergeometric formula C(K,k) × C(N−K, n−k) / C(N,n).
Choose a scenario and enter the parameters. The tool returns the probability as a fraction, a decimal, a percentage, and odds (1 in N). Use it for homework, games, statistics, and any "what are the chances" question.