The Excel GAMMAINV function returns the inverse of the gamma cumulative distribution — given a probability, it finds the x value. It is a legacy function; Microsoft replaced it in Excel 2010 with GAMMA.INV, which takes the same arguments.
Syntax
| Argument | Description | |
|---|---|---|
probability | Required | A probability associated with the gamma distribution, between 0 and 1. |
alpha | Required | The shape parameter (must be > 0). |
beta | Required | The scale parameter (must be > 0). Use beta = 1 for the standard gamma distribution. |
How to use it
GAMMAINV is the reverse of GAMMADIST (cumulative form): you supply a probability and the shape and scale parameters, and it returns the x at which the cumulative gamma distribution reaches that probability.
Because it inverts the CDF, feeding the output of GAMMADIST(...,TRUE) back into GAMMAINV returns your original x (within rounding). The probability argument must be between 0 and 1.
Use GAMMA.INV in Excel 2010 and later. GAMMAINV is retained only for backward compatibility. Microsoft recommends GAMMA.INV, which has the same three arguments and better precision.
Try it: interactive demo
Pick a GAMMAINV example to see the formula and its result.
Practice workbook
Frequently asked questions
Should I use GAMMAINV or GAMMA.INV?
GAMMA.INV in Excel 2010 or later. It takes the same probability, alpha, beta arguments and is the supported function; GAMMAINV is kept only for older workbooks.How does GAMMAINV relate to GAMMADIST?
GAMMADIST(x,alpha,beta,TRUE) turns an x into a probability; GAMMAINV(probability,alpha,beta) turns that probability back into x.What range must the probability be in?
probability argument must be between 0 and 1. Values outside that range, or non-numeric inputs, return an error.Does GAMMAINV solve iteratively?
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