GAMMADIST Function (OpenOffice Calc)

• Introduced: First release not established. The OpenOffice.org 3.3 function appendix documents this name; historical presence does not prove introduction.
• Supported in: Apache OpenOffice 4.1.16. No final supported release has been established.
• Scope: Desktop Calc. Current argument defaults are stated for the cited release, not inferred for every older version.
• Checked: October 14, 2026. Official documentation/source and independent mathematics checked; Apache OpenOffice Calc was not run for this guide.

A gamma distribution models a nonnegative continuous quantity with positive shape Alpha and positive scale Beta. Scale uses the same units as Number. It is not a rate: a rate λ corresponds to scale 1/λ. The mean is Alpha×Beta and the variance is Alpha×Beta². Official reference.

For x>0, density is x^(Alpha−1)×exp(−x/Beta)/(Γ(Alpha)×Beta^Alpha). Cumulative probability is the integral from zero to x. A density describes curve height per measurement unit, not the probability of observing exactly x.

=GAMMADIST(Number; Alpha; Beta [; Cumulative])

The first three arguments are required. Alpha and Beta must be strictly positive. The pinned evaluator allows three or four arguments and defaults to cumulative probability. Use 1 for cumulative probability and 0 for density. The wiki presents the four-argument form, while the release implementation also permits the three-argument default shown here.

Enter each formula in a separate cell. Expected values are independent mathematical references rounded to twelve decimal places.

Put elapsed time 3 in A2, shape 2 in B2 and scale 2 in C2. In D2 enter =GAMMADIST(A2;B2;C2;1), expected 0.442174599629. For an hours-based model that means about 44.22% probability of completion by hour three. It does not establish that a real process follows this distribution.

The corresponding density =GAMMADIST(A2;B2;C2;0) is approximately 0.167347620111 per hour. Keep probability and density in separate labeled columns. Formatting a density as a percentage does not turn it into a probability.

For the same shape and scale, =GAMMADIST(5;2;2;1)-GAMMADIST(3;2;2;1) gives approximately 0.270527905187. Keep the larger endpoint first and the parameters fixed. A negative result often signals reversed bounds rather than an impossible probability model.

To find a cutoff instead, =GAMMAINV(0.8;2.5;1.4) gives approximately 5.102493288654. Feeding that full result into GAMMADIST with shape 2.5 and scale 1.4 should recover 0.8. Inverse quantiles and densities answer different questions.

The release helpers return zero cumulative probability for x≤0 and zero density for x<0. At x=0, the Apache OpenOffice 4.1.16 density helper also returns zero for every positive shape. This source convention differs from the mathematical right-hand density limit when Alpha=1 (1/Beta) or Alpha<1 (unbounded). Do not use that endpoint as proof of the mathematical limit. These are source-derived statements, not native observations.

For an ordinary gamma model use nonnegative measurements, positive shape/scale, and check the intended density or CDF selector. Do not copy every boundary rule from Excel or another Calc version by analogy.

Shape 1 reduces to an exponential model: for Beta=2 and x=3 the CDF is 1−exp(−1.5), approximately 0.776869839852. If a reference specifies rate 0.5, enter Beta=2, not Beta=0.5.

Subtracting a CDF extremely close to 1 can erase a tiny survival probability, and very large arguments can stress intermediate arithmetic. The reference examples do not certify extreme tails, all imported types or every locale. Keep unrounded intermediate values and verify demanding ranges in the actual installed release.

• GAMMADIST documentation
• Apache OpenOffice 4.1.16 evaluator and argument contract