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GAMMAINV Function
Summary
The GAMMAINV function calculates the inverse of the gamma cumulative distribution, returning the value x where the cumulative probability equals a specified value. Ideal for statistical analysis of skewed distributions.
Syntax
GAMMAINV(probability, alpha, beta)Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
| probability | Number |
Yes | Probability value (0 < probability < 1) for which to find the inverse gamma value |
| alpha | Number |
Yes | Alpha shape parameter (> 0) |
| beta | Number |
Yes | Beta scale parameter (> 0). If beta=1, returns standard gamma distribution |
Using the GAMMAINV Function
GAMMAINV is used in statistical modeling to find critical values in gamma distributions, commonly applied in quality control, reliability analysis, and waiting time studies where data shows right-skewness.
Common GAMMAINV Examples
Basic Inverse Gamma Calculation
=GAMMAINV(0.068094, 9, 2)Returns approximately 10, finding the value where gamma cumulative distribution equals 0.068094 with alpha=9, beta=2.
Standard Gamma Distribution
=GAMMAINV(0.5, 5, 1)Finds median of standard gamma distribution (beta=1) with shape parameter 5.
Error Handling Example
=IFERROR(GAMMAINV(A1,B1,C1), "Invalid input")Safely handles invalid probability, alpha, or beta values.
Frequently Asked Questions
Common Errors and Solutions
#VALUE!
Cause: Any argument is non-numeric or text
Solution: Ensure all inputs are valid numbers
#NUM!
Cause: Probability <0 or >1, or alpha≤0, or beta≤0
Solution: Verify probability between 0-1 and parameters positive
#N/A
Cause: Iterative search fails to converge after 100 iterations
Solution: Check parameter values and precision requirements
Notes
- Deprecated function - prefer GAMMA.INV for new workbooks
- Uses iterative algorithm with maximum 100 iterations
- Precision depends on GAMMADIST function accuracy
- If p = GAMMADIST(x,alpha,beta,TRUE), then GAMMAINV(p,alpha,beta) ≈ x
Compatibility
Available in: Excel 2007, Excel 2010, Excel 2013, Excel 2016
Not available in: Excel 2021, Microsoft 365, Excel 2019 (prefer GAMMA.INV)
Content last reviewed: December 9, 2025
Update frequency: As needed
Excel versions tested: Excel 2007, Excel 2010, Excel 2013, Excel 2016