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Probability of either event calculator
Calculate union probability for two events with a stated overlap.
On this page
Probability of A or B0.6
Percentage60%
Calculator controls
How to calculate
Calculate union probability for two events with a stated overlap.
Probability of A or B = a+b-both; Percentage = (a+b-both)*100
Worked example
Probability of A: 0.4; Probability of B: 0.3; Probability of both: 0.1.
Probability of A or B: 0.6 ; Percentage: 60 %.
Assumptions and limits
Inputs must describe a consistent probability model; the overlap cannot exceed either individual probability and the union cannot exceed one.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Calculate union probability for two events with a stated overlap. The displayed figures use the inputs and formula shown on this page.
When this tool is useful
Use the probability of either event to compare a scenario, check an estimate, or verify a manual calculation.
Understanding your inputs
| Input | What to enter |
|---|---|
| Probability of A | Enter a number of at least 0 and no more than 1. |
| Probability of B | Enter a number of at least 0 and no more than 1. |
| Probability of both | Enter a number of at least 0 and no more than 1. |
Frequently asked questions
What should I check before using the probability of either event result?
Inputs must describe a consistent probability model; the overlap cannot exceed either individual probability and the union cannot exceed one.
Is this probability of either event result exact?
It is exact for the stated mathematical model and entered values. Real-world results can differ when rates, timing, fees, definitions or measurement conditions differ.