Syntax
GAMMA.INV(probability, alpha, beta)
| Parameter | Description |
|---|---|
| probability | Parameter of the GAMMA.INV function. |
| alpha | Parameter of the GAMMA.INV function. |
| beta | Parameter of the GAMMA.INV function. |
Examples
90th percentile wait time
Formula
=GAMMA.INV(0.9, 3, 2)
Returns ~10.05. If customer service wait time follows a gamma with shape=3, scale=2, 90% of customers wait less than about 10 minutes.
Insurance claim threshold
Formula
=GAMMA.INV(0.95, 2, 5000)
Returns ~29,957. 95% of claims fall below about $30,000 under this gamma model — useful for setting reserve levels.
Median of gamma distribution
Formula
=GAMMA.INV(0.5, 4, 1)
Returns ~3.672. The median of a gamma(4,1) distribution is about 3.67, slightly less than the mean of 4.
Common Errors
#NUM!
Probability must be between 0 and 1 (inclusive). Alpha and beta must be positive.
#VALUE!
Occurs when arguments are non-numeric.
Tips
Inverse of GAMMA.DIST
GAMMA.INV is the inverse of GAMMA.DIST with cumulative=TRUE. That is, GAMMA.INV(GAMMA.DIST(x, a, b, TRUE), a, b) = x.
Use for simulation
Generate gamma-distributed random values with =GAMMA.INV(RAND(), alpha, beta). Useful for Monte Carlo simulations of processes with gamma-distributed durations.
Quantile-based planning
Use GAMMA.INV to set capacity or reserves. For example, GAMMA.INV(0.99, alpha, beta) gives a level that covers 99% of cases.
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