Why this tool is useful
Combine two event rates without double-counting observations that belong to both events.
Everyday Calculators · runs locally
Union Probability Calculator
Calculate the probability of A or B while subtracting an explicitly entered overlap.
Ready. Your working data stays in this browser.
How it works
It applies P(A ∪ B) = P(A) + P(B) - P(A ∩ B).
Practical example
40% plus 35% with a 10% overlap produces a 65% union.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.