Probability Calculator (Two Events)
Enter the probability of events A and B (as percentages) to see combined probabilities for independent events.
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Probability Calculator (Two Events) by TheCalcTools
How the Probability Calculator (Two Events) works
Enter each event’s probability as a percentage.
For independent events, the probability of both is the product of the two.
The probability of at least one is found by inclusion-exclusion.
The formula
Worked example
Using the default values shown in the calculator:
| P(A) (%) | 40 |
|---|---|
| P(B) (%) | 25 |
- P(A and B) = 40% × 25% = 10.0%.
- P(A or B) = 40% + 25% − 10% = 55.0%.
- P(neither) = 60% × 75% = 45.0%.
Result:
| A and B | 10.00% |
|---|---|
| A or B (at least one) | 55.00% |
| Neither A nor B | 45.00% |
| A but not B | 30.00% |
| Exactly one of A, B | 45.00% |
Frequently asked questions
What does independent mean?
Knowing that A happened does not change the chance of B. Two separate coin flips are independent.
What if the events are not independent?
Then P(A and B) needs the conditional probability. See the Bayes’ theorem calculator.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.