How it works
Estimate the probability of exactly k events under a Poisson model with a constant rate and independent occurrences.
P(X=k) = e⁻λ λᵏ/k!
Worked example
Show example inputs and result
Expected events: 3 · Exact events: 2.
- Result
- 0.22404181
Questions and answers
Why are some results rounded?
Results display up to 8 decimal places. Calculations use the unrounded values; very small values use scientific notation. JavaScript floating-point arithmetic can introduce tiny rounding differences.
Are my inputs sent to a server?
The calculator processes inputs in your browser. Its code does not send your values to a server.
Method reviewed: October 8, 2026 · Methods & accuracy