In this article
POISSON returns the Poisson probability. It is a compatibility function: Excel keeps it so workbooks from Excel 2007 and earlier still calculate, but Microsoft recommends POISSON.DIST for new work. Both give the same result.
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Syntax
=POISSON(x, mean, cumulative)| Argument | What it means |
|---|---|
x |
Events |
mean |
Average |
cumulative |
TRUE/FALSE |
Examples
Example 1
=ROUND(POISSON(A2,B2,FALSE),4)Result: 0.1804. See the worked example table below for more cases.
💡 For new workbooks use POISSON.DIST: it gives the same answer and is the name Microsoft keeps documenting.
POISSON in practice
Where you will use it
- Opening and checking older workbooks that use POISSON
- Understanding formulas shared by colleagues on older Excel versions
- Knowing when to swap in POISSON.DIST for clarity
Worked example
| k | Mean | Formula | Result |
|---|---|---|---|
| 3 | 2 | =ROUND(POISSON(A2,B2,FALSE),4) | 0.1804 |
| 0 | 2 | =ROUND(POISSON(A3,B3,FALSE),4) | 0.1353 |
| 5 | 4 | =ROUND(POISSON(A4,B4,FALSE),4) | 0.1563 |
Results calculated in Excel. Same result as POISSON.DIST.
Mistakes people make
| Mistake | What to do instead |
|---|---|
| Using POISSON in new files | Prefer POISSON.DIST: same result, clearer name, and the function Microsoft keeps improving |
| Mixing old and new names in one model | Pick one style per workbook so formulas are easy to audit |
Related functions
📚 Part of the free Excel course: Beginner → Expert · Try it in the Formula Lab or ask the AI Helper.
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