Returns the inverse of the gamma cumulative distribution. If p = GAMMADIST(x,...), then GAMMAINV(p,...) = x.
You can use this function to study a variable whose distribution may be skewed.
Important This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. Although this function is still available for backward compatibility, you should consider using the new functions from now on, because this function may not be available in future versions of Excel.
For more information about the new function, see GAMMA.INV function.
Syntax
GAMMAINV(probability,alpha,beta)
The GAMMAINV function syntax has the following arguments (argument: A value that provides information to an action, an event, a method, a property, a function, or a procedure.):
 Probability Required. The probability associated with the gamma distribution.
 Alpha Required. A parameter to the distribution.
 Beta Required. A parameter to the distribution. If beta = 1, GAMMAINV returns the standard gamma distribution.
Remarks
 If any argument is text, GAMMAINV returns the #VALUE! error value.
 If probability < 0 or probability > 1, GAMMAINV returns the #NUM! error value.
 If alpha ≤ 0 or if beta ≤ 0, GAMMAINV returns the #NUM! error value.
Given a value for probability, GAMMAINV seeks that value x such that GAMMADIST(x, alpha, beta, TRUE) = probability. Thus, precision of GAMMAINV depends on precision of GAMMADIST. GAMMAINV uses an iterative search technique. If the search has not converged after 100 iterations, the function returns the #N/A error value.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How do I copy an example?
 Select the example in this article. If you are copying the example in Excel Online, copy and paste one cell at a time.
Important: Do not select the row or column headers.
Selecting an example from Help
 Press CTRL+C.
 Create a blank workbook or worksheet.
 In the worksheet, select cell A1, and press CTRL+V. If you are working in Excel Online, repeat copying and pasting for each cell in the example.
Important: For the example to work properly, you must paste it into cell A1 of the worksheet.
 To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.
After you copy the example to a blank worksheet, you can adapt it to suit your needs.

A 
B 
Data 
Description 
0.068094 
Probability associated with the gamma distribution 
9 
Alpha parameter to the distribution 
2 
Beta parameter to the distribution 
Formula 
Description (Result) 
=GAMMAINV(A2,A3,A4) 
Inverse of the gamma cumulative distribution for the above terms (10.00001131) 
