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GAMMA.INV Function
Summary
The GAMMA.INV function returns the inverse of the gamma cumulative distribution, solving for the value x where GAMMA.DIST(x,alpha,beta,TRUE) equals a specified probability. Ideal for statistical analysis of skewed distributions like waiting times or project durations.
Syntax
GAMMA.INV(probability,alpha,beta)Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
| probability | Number |
Yes | Probability value (0 < probability < 1) for the gamma distribution |
| alpha | Number |
Yes | Shape parameter defining distribution shape (alpha > 0) |
| beta | Number |
Yes | Scale parameter controlling spread (beta > 0). When beta=1, returns standard gamma. |
Using the GAMMA.INV Function
GAMMA.INV is essential for inverse probability calculations in gamma-distributed data analysis. Use it to find critical values for given probabilities in quality control, reliability engineering, and financial modeling of skewed datasets.
Common GAMMA.INV Examples
Basic Inverse Gamma Calculation
=GAMMA.INV(0.068094,9,2)Returns approximately 10, the value where cumulative gamma probability reaches 6.81% for alpha=9, beta=2.
Standard Gamma Distribution
=GAMMA.INV(0.5,5,1)Finds median (50th percentile) of standard gamma distribution with shape=5.
Project Management Threshold
=GAMMA.INV(0.95,3.2,4.5)Calculates 95th percentile completion time for project with gamma-distributed duration.
Frequently Asked Questions
Common Errors and Solutions
#VALUE!
Cause: Any argument contains text
Solution: Ensure all inputs are numeric values
#NUM!
Cause: probability ≤ 0 or ≥ 1, or alpha ≤ 0, or beta ≤ 0
Solution: Verify probability between 0-1 exclusive, alpha>0, beta>0
#N/A
Cause: Iterative search fails to converge after 64 iterations
Solution: Check parameter values; try different starting probability
Notes
- Uses iterative algorithm with 64-iteration convergence limit
- Precision depends on GAMMA.DIST accuracy
- Perfect complement to GAMMA.DIST for complete gamma analysis
- Available in Excel 2007 and later versions
Compatibility
Available in: Excel 2007, Excel 2010, Excel 2013, Excel 2016, Excel 2019, Excel 2021, Microsoft 365
Not available in: Excel 2003 and earlier
Content last reviewed: December 9, 2025
Update frequency: As needed
Excel versions tested: Excel 2007+