PlanMaker GAMMA.DIST Function: Gamma densities and cumulative probabilities

=GAMMA.DIST(X, Alpha, Beta, Cumulative)
=GAMMADIST(X, Alpha, Beta, Cumulative)

All four arguments are required. The official domain is X≥0 and both parameters greater than 0. TRUE selects the left-tail cumulative distribution; FALSE selects density.

The short reference calls both Alpha and Beta shape parameters, without explaining their distinct roles. In the standard shape-scale gamma parameterization used for these checks, Alpha is dimensionless shape and Beta is scale in the same units as X. A rate parameter is instead 1/Beta. The native scaled examples agree with the shape-scale interpretation, resolving that distinction for the tested cases rather than relying on the ambiguous wording.

For shape a and scale b, the independent mean is a×b and variance a×b². Thus shape 2, scale 2 gives mean 4 and variance 8. Those are model properties, not extra function arguments.

Enter 4 in B2, 2 in B3, and 2 in B4. Use =GAMMA.DIST(B2,B3,B4,TRUE) in B6 and the FALSE version in B7.

For shape 2 and scale 2, the independent equations simplify to:

CDF(x) = 1-exp(-x/2)*(1+x/2)
PDF(x) = (x/4)*exp(-x/2)

At x=4, these give CDF≈0.5939941503 and density≈0.1353352832. The legacy GAMMADIST calls are paired with both calculations. These closed forms are mathematical controls for the stated shape; they are not a trace of proprietary implementation code.

With shape 1 and scale 2, the model becomes exponential with rate 1/2. =GAMMA.DIST(2,1,2,TRUE) is therefore independently 1−exp(−1)≈0.6321205588. If Beta were a rate 2 instead, this result would differ substantially; the example checks the scale interpretation directly.

For shape 2 and scale 2, the probability between 2 and 4 is the difference of cumulative values. The independent CDF at 2 is 1−2/e≈0.2642411177, so the interval probability is approximately 0.3297530326.

=GAMMA.DIST(4,2,2,TRUE)-GAMMA.DIST(2,2,2,TRUE)

Do not subtract densities to obtain an interval probability. A density has inverse measurement units; its integral over an interval gives probability. At an exact point, a continuous model assigns probability zero even when its density is positive.

The probability above 4 is the complementary value 3×exp(−2)≈0.4060058497. For more extreme tails, subtracting a CDF very near 1 can lose significant digits. The moderate controls here do not establish all tail precision or underflow behavior.

For shape 1 and scale 2, the right-hand density at 0 is 0.5. For shape 2, density at 0 is 0. The independent origin checks are:

When 0<Alpha<1, density diverges as X approaches 0 from the right. In this build, =GAMMA.DIST(0,0.5,2,FALSE) returns #NUM!. That is an application observation; the mathematical singularity alone would not determine the error token.

Negative X or nonpositive Alpha/Beta violates the documented domain. The tested calls =GAMMA.DIST(-1,2,2,TRUE) and =GAMMA.DIST(4,0,2,TRUE) both return #NUM!. Text coercion, omitted flags, and arbitrary nonlogical cumulative arguments are not established by the bounded examples.

A gamma model may describe positive observations, but this function neither estimates the parameters nor verifies that the model fits a dataset. Do not interpret a density as a failure probability or an individual-outcome prediction. Keep the units of X and Beta consistent and do not substitute a rate without taking its reciprocal.

The official GAMMADIST page explicitly calls GAMMA.DIST identical. The legacy name is not declared retired. The Excel compatibility note for the dotted spelling does not date PlanMaker’s introduction of the function.

GAMMA.INV converts a left-tail gamma probability into a quantile. EXP expresses the simple shape 1 and shape 2 controls. WEIBULL.DIST is a different positive distribution whose shape and scale must not be reused without changing the model. Use your locale’s argument separators.

The native shape 2/scale 2 CDF at 4 is approximately 0.593994150290162, and its density approximately 0.135335283236613. GAMMADIST returns the same saved values. The shape 1/scale 2 CDF at 2 is approximately 0.632120548780792, close to the independent 1−exp(−1) reference rather than identical at every digit. The three origin controls returned 0.5, 0, 0 as listed.

FreeOffice PlanMaker 2024 rev F1238.1005: selected cell J2 contains =GAMMA.DIST(4,2,2,TRUE) and displays 0.59399. Raw saved values retain more digits; rounded display values are not asserted as exact mathematical equality.

Official FreeOffice PlanMaker 2024 references checked October 18, 2026: reference 1, reference 2. The first introduction release is unknown from these references. Current documentation does not imply retirement or identical behavior in every other edition.

The 11 selected formula cells for this function were tested on October 18, 2026 in FreeOffice PlanMaker 2024 rev F1238.1005, 64-bit, then saved in PMDX format and reopened with calculation meaning preserved. Paired legacy calls were included. Native observations remain distinct from independent mathematical references, teaching layouts, and advanced examples not individually executed. The proprietary implementation has not been inspected; the bounded results do not establish every tail, parameter, input type, edition, or export behavior.