Probability Calculator
Calculate probabilities for independent events: combined probability of A and B, A or B, neither, and conditional probability.
Inputs
Enter 0.5 or 50 for 50%.
P(A AND B)
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P(A OR B)
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P(NEITHER A NOR B)
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P(exactly one)
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P(NOT A)
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Odds of A AND B
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About Probability Calculator
Assuming independence
These formulas assume A and B are independent — one doesn’t affect the other. If events are dependent (e.g., card draws without replacement), use conditional probability: P(A AND B) = P(A) × P(B|A).
P(A OR B) — why subtract?
P(A) + P(B) double-counts the overlap. Subtracting P(A AND B) removes the double-count. This is the inclusion-exclusion principle.
Common applications
Reliability engineering (probability a system fails). Disease screening (true positive rates). Insurance (probability of multiple claims). Games (chance of getting at least one specific card in N draws).