Probability Calculator
Combine two independent event probabilities: and, or, neither.
Results update as you type.
About this calculator
This calculator takes the probability of two independent events A and B and works out the key combined probabilities: both happening (A and B), at least one happening (A or B), and neither happening. It assumes the events are independent, meaning one occurring does not change the chance of the other. Enter each probability as a percentage between 0 and 100.
Frequently asked questions
How do I find the probability of two events both happening?
For independent events, multiply their probabilities: P(A and B) = P(A) · P(B). A 50% event and a 30% event both occurring is 0.5 × 0.3 = 0.15, or 15%.
What does independent mean here?
Independent means the outcome of one event has no effect on the other — like two separate coin flips. If the events influence each other (are dependent), these formulas do not apply and you need conditional probabilities.
How is "A or B" calculated?
P(A or B) = P(A) + P(B) − P(A and B). Subtracting the overlap prevents the shared outcome from being counted twice, so the result never exceeds 100%.
Results are estimates for general guidance only, not financial, medical or tax advice.