Free probability calculator: instantly find P(A and B), P(A or B) and conditional probabilities for independent or dependent events with clear results.
Probability questions show up everywhere: the chance it rains and traffic is heavy, the odds of drawing an ace, or the chance at least one of two independent events happens. The common mistakes are double-counting overlaps and confusing independent with conditional events.
This probability calculator handles two events, A and B, and returns P(A and B), P(A or B) and both conditional probabilities. Switch between independent and dependent events — for dependent events, enter P(B|A), the probability of B given that A has already happened.
Students use it for statistics homework, while anyone making everyday forecasts can check their intuition against the numbers.
Enter both probabilities as percentages (0-100) and choose the relationship between the events; all results update instantly.
Add the two probabilities, then subtract the overlap: P(A or B) = P(A) + P(B) − P(A and B). Without subtracting, the overlap is counted twice.
Events are independent when one does not change the probability of the other: P(A|B) = P(A), so P(A and B) = P(A) × P(B). Two coin flips are a classic example.
P(A|B) = P(A and B) / P(B): the probability that A happens given that B has already happened. It only makes sense when P(B) > 0.
For independent events, multiply: P(A and B and C) = P(A) × P(B) × P(C). For the union of three events use inclusion-exclusion: P(A∪B∪C) = P(A)+P(B)+P(C) − P(A∩B) − P(A∩C) − P(B∩C) + P(A∩B∩C).