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Excel POISSON Function

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The Excel POISSON function returns the Poisson distribution which is used to predict the number of events occurring over a specific time, e.g., the number of people arriving at the market in 10 minutes.

Note: This function has been replaced with POISSON.DIST function that may provide improved accuracy after Excel 2010 version. This function is still can be available but considering it may be not available in the future, you should better study to use the new function from now.

Formula syntax



  • X: Required, the number of events.
  • Mean: Required, the expected numeric value.
  • Cumulative: Required, a logical value that determines the form of the probability distribution returned.
    TRUE: returns the cumulative Poisson probability that the number of random events occurring will be between 0 and x inclusive;
    FALSE: returns the Poisson probability mass function that the number of events occurring will be exactly x.


POISSON function returns a numeric value.


1. If x is not an integer, it will be truncated.

2. If x or mean is non-numeric, the #VALUE! error value will be returned.

3. If x < 0 or mean < 0, the #NUM! error value will be returned.

4. POISSON.DIST is calculated as the following equations:

For cumulative = TRUE
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for cumulative = FALSE
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Excel 2007

Usage and Examples

Basic usage

Based on the given number of events and expected mean in cells B3 and B5, you can get the cumulative Poisson probability (cumulative as TRUE) and Poisson probability mass function (cumulative as FALSE) by using the POISSON function as below:


Or directly use numbers in the function

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Or directly use numbers in the function

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Press Enter key to get result.

Other Functions:

  • Excel F.INV Function
    The Excel F.INV function returns the inverse of F probability distribution. If p (probability) = F.DIST(x,…), then F.INV(p,…)= x.

  • Excel FDIST Function
    The Excel FDIST Function returns the (right-tailed) F probability distribution which is usually used to measure the degree of diversity between two data sets.

  • Excel EXPON.DIST Function
    EXPON.DIST function used in Excel 2010, returns the exponential distribution based on the given x value and the parameter of the distribution.

  • Excel F.DIST Function
    The Excel F.DIST function returns the F probability distribution which is usually used to measure the degree of diversity between two data sets.


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