How to use this calculator
Choose an event calculation and enter probabilities from 0 to 1.
Formula and method
Union P(A∪B)=P(A)+P(B)−P(A∩B); binomial P(X=k)=C(n,k)p^k(1−p)^(n−k).
Worked example
P(A)=0.4, P(B)=0.5, P(both)=0.2 gives union probability 0.7.
Assumptions and supported scope
Probabilities must be coherent. Repeated-event mode assumes independent identical trials, n≤500; table shows at most 51 outcomes. Ordinary floating-point precision applies near extreme tails.
Method references
Method and worked example checked against the calculator implementation. About our methods · Report a correction