The GAMMA.DIST function returns the gamma distribution. You can use this function to study variables that may have a skewed distribution. The gamma distribution is commonly used in queuing analysis.
Syntax:= GAMMADIST(x,alpha,beta,cumulative)
The GAMMA.DIST function syntax has the following arguments:
 X Required. The value at which you want to evaluate the distribution.
 Alpha Required. A parameter to the distribution.
 Beta Required. A parameter to the distribution. If beta = 1, GAMMA.DIST returns the standard gamma distribution.

Cumulative Required. A logical value that determines the form of the function. If cumulative is TRUE, GAMMA.DIST returns the cumulative distribution function; if FALSE, it returns the probability density function.
Example: Let’s look at some Excel GAMMA.DIST function examples and explore how to use the GAMMA.DIST function as a worksheet function in Microsoft Excel:
Syntax: =GAMMA.DIST(B1,B2,B3,FALSE)
Result: 0.112020904
Based on the Excel spreadsheet above, the following GAMMA.DIST examples would return:
Syntax: =GAMMA.DIST(B1,B2,B3,FALSE)
Result: 0.112020904
Syntax: =GAMMA.DIST(B1,B2,B3,TRUE)
Result: 0.576809919
Note:
 If x, alpha, or beta is nonnumeric, GAMMA.DIST returns the #VALUE! error value.
 If x < 0, GAMMA.DIST returns the #NUM! error value.
 If alpha ≤ 0 or if beta ≤ 0, GAMMA.DIST returns the #NUM! error value.

The equation for the gamma probability density function is:
The standard gamma probability density function is:  When alpha = 1, GAMMADIST returns the exponential distribution with:
 For a positive integer n, when alpha = n/2, beta = 2, and cumulative = TRUE, GAMMA.DIST returns (1 – CHISQ.DIST.RT(x)) with n degrees of freedom.

When alpha is a positive integer, GAMMA.DIST is also known as the Erlang distribution.