Probability Calculator
Calculate the probability of events A and B (intersection, union, either, neither, or conditional) assuming independence. Enter each probability between 0 and 1, then choose the operation.
Your Result
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| Result | What it means? |
|---|---|
| 0 | Impossible The probability is 0 — the event cannot occur. |
| < 10% | Very unlikely A probability below 10% — the event is rare but possible. |
| 10 – 40% | Unlikely A probability between 10% and 40% — the event is not expected. |
| 40 – 60% | Roughly even A probability between 40% and 60% — the event is a coin flip. |
| 60 – 90% | Likely A probability between 60% and 90% — the event is expected. |
| ≥ 90% | Very likely A probability of 90% or higher — the event is nearly certain. |
| 1 | Certain The probability is 1 — the event will occur. |
| — | No result Inputs are out of range or missing. |
Probability Formulas (independent events)
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Intersection: P(A∩B) = pA·pB. Union: P(A∪B) = pA + pB − pA·pB. Either: pA + pB − 2·pA·pB. Neither: (1−pA)·(1−pB). Conditional: pA (independent).
- All formulas assume events A and B are independent. For dependent events, supply P(A∩B) directly and use the definitions instead.
- Under independence, P(A|B) = P(A) — knowing that B occurred does not change the probability of A.
This calculator evaluates basic probability expressions assuming independent events. It does not store or transmit your inputs — every calculation runs entirely in your browser.