# WorksheetFunction.Poisson Method (Excel)

Office 2013

Returns the Poisson distribution. A common application of the Poisson distribution is predicting the number of events over a specific time, such as the number of cars arriving at a toll plaza in 1 minute.

Important

This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. This function is still available for compatibility with earlier versions of Excel. However, if backward compatibility is not required, you should consider using the new functions from now on, because they more accurately describe their functionality.

## Syntax

expression .Poisson(Arg1, Arg2, Arg3)

expression A variable that represents a WorksheetFunction object.

### Parameters

Name

Required/Optional

Data Type

Description

Arg1

Required

Double

X - the number of events.

Arg2

Required

Double

Mean - the expected numeric value.

Arg3

Required

Boolean

Cumulative - a logical value that determines the form of the probability distribution returned. If cumulative is TRUE, POISSON returns the cumulative Poisson probability that the number of random events occurring will be between zero and x inclusive; if FALSE, it returns the Poisson probability mass function that the number of events occurring will be exactly x.

Double

## Remarks

• If x is not an integer, it is truncated.

• If x or mean is nonnumeric, POISSON returns the #VALUE! error value.

• If x < 0, POISSON returns the #NUM! error value.

• If mean ≤ 0, POISSON returns the #NUM! error value.

• POISSON is calculated as follows. For cumulative = FALSE: For cumulative = TRUE: