Independent Event Probability Calculator
Calculate the probabilities of both, either, neither, or exactly one of two independent events.
Your result
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How to use this calculator
- Enter your values in the labeled fields, keeping the displayed units.
- Choose Calculate or press Enter in a single-line field.
- Review the result and the assumptions below before using it.
Formula and method
For independent events, P(A and B) = P(A) × P(B). P(A or B) = P(A) + P(B) − P(A and B).
Worked example
With probabilities of 50% and 25%, both occur with probability 12.5% and at least one with probability 62.5%.
What the result assumes
Independence is required. This model is not suitable for dependent events such as drawing cards without replacement.
Common question
Does “either” exclude both events occurring?
Here, at least one includes both. The separate exactly-one result excludes the overlap.