Probability Calculator
Find the probability of two independent events both happening, or at least one happening.
The formulas (independent events)
P(A and B) = P(A) × P(B) — the chance both independent events occur.
P(A or B) = P(A) + P(B) − P(A and B) — the chance at least one occurs. The overlap is subtracted once so it isn't double-counted.
Worked example
If P(A) = 0.3 and P(B) = 0.4, then P(A and B) = 0.3 × 0.4 = 0.12, and P(A or B) = 0.3 + 0.4 − 0.12 = 0.58.
Frequently asked questions
What does 'independent events' mean?
Two events are independent if the outcome of one doesn't affect the probability of the other — like two separate coin flips, or drawing a card and rolling a die.
Does this work for dependent events?
No. This calculator assumes independence. For dependent events (like drawing two cards from a deck without replacement), the second probability changes based on the first outcome, which needs a different calculation.