The probability that A or B (or both) occur: P(A∪B) = P(A) + P(B) − P(A∩B).

The probability that both A and B occur. For independent events, P(A∩B) = P(A)·P(B). For mutually exclusive events, it is 0.

What is conditional probability?

P(A|B) = P(A∩B) / P(B) — the probability of A given that B has occurred.

How do I model mutually exclusive events?

Enter P(A∩B) = 0 (or uncheck independent and set the field to 0). The union then simplifies to P(A) + P(B).

No — everything is computed locally in your browser.

P(A), P(A∪B), P(A∩B) — single and joint event probability.

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Follow these steps — everything happens instantly in your browser.

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Step 1. Enter P(A) and P(B) as decimals between 0 and 1 (e.g. 0.5 for 50%).
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Step 2. Enter P(A∩B) directly, or check 'independent' to compute it as P(A)·P(B).
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Step 3. See union, complement and conditional probabilities update instantly.

Everything you might want to know about probability calculator.

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