## Summary

The Excel TRIMMEAN function returns the mean of the interior of a data set. The function calculates the mean by excluding a percentage of data points from the top and bottom tails of a data set. Use this function when you need to exclude outlying data from your analysis.

## Syntax

=TRIMMEAN (array, percent)

## Syntax Breakdown

Array
Required. Array or range of values to trim and average.

Percent
Required. Fractional number of data points to exclude from the calculation. For example, if percent = 0.3, 15 points are trimmed from a data set of 50 points (50 * 0.3).

If the percent argument is < 0 or > 1, the function returns the #NUM! error.

## Usage Notes

TRIMMEAN calculates the mean, or average, of a set of numbers while removing outliers. The number of data points to be excluded is provided in the percent argument. The function will first exclude values from the top and bottom of the data set prior to calculating the mean.

The function will round excluded data points down to the nearest multiple of 2. For example, in our prior example with percent = 0.3 and 50 data points, a total of 15 points should be excluded. Excel will round 15 down to 14, then exclude seven values from the top and seven values from the bottom of the data set.