GAMMADIST in WPS Spreadsheet: Gamma Cumulative Probabilities and Densities

=GAMMADIST(x,alpha,beta,cumulative)

alpha is the positive shape and beta is the positive scale. The printed official density uses exp(−x/beta) divided by beta raised to alpha; that establishes scale rather than rate. For a rate λ, the corresponding scale is 1/λ, not λ.

TRUE requests the lower cumulative probability P(X ≤ x). FALSE requests the density at x. Always supply the logical mode explicitly in these examples. They use positive x and positive integer shape, also called the Erlang case in the lesson.

If x is measured in minutes, beta is in minutes, shape is dimensionless, the CDF is dimensionless and the density has units per minute. A density at one point is not the probability of that exact point.

In a fresh sheet enter A2 = 4, B2 = 2 and C2 = 2, all numeric. Label them x, Shape and Scale. Enter:

• D2: =GAMMADIST(A2,B2,C2,TRUE); expected approximately 0.5939941503.
• E2: =GAMMADIST(A2,B2,C2,FALSE); expected approximately 0.1353352832.

For shape 2 and scale 2, the density is x×exp(−x/2)/4, and the CDF is 1−exp(−x/2)×(1+x/2). At x = 4 these become exp(−2) and 1−3exp(−2), respectively. The density is therefore approximately 0.1353352832.

For the shape-2, scale-2 model, the probability between 2 and 4 is the CDF difference: 0.5939941503 − 0.2642411177 = 0.3297530326 approximately. It is not the difference between the two densities. The probability above 4 is the complement of the CDF, approximately 0.4060058497.

These calculations assume that a gamma model with these parameters has already been chosen. The function does not estimate parameters, test fit or certify a queueing model. Shape 1 reduces mathematically to an exponential distribution with rate 1/beta, providing the final table row as a separate check.

The lesson documents #VALUE! for nonnumeric x, alpha or beta; #NUM! for x < 0, alpha ≤ 0 or beta ≤ 0. Two bounded documented controls are =GAMMADIST(-1,2,2,TRUE) and =GAMMADIST(4,0,2,TRUE), both expected #NUM!.

The examples do not establish the density at x = 0 for every shape, omitted-mode behavior, Boolean coercion or extreme-tail accuracy. The walkthrough displays a CDF of 1 at a very large positive x; a rounded display does not prove that the exact mathematical tail is zero. The lesson’s shorthand CHIDIST relationship is not needed for the original calculations here, and no dotted-name alias is presumed.

The official WPS Academy GAMMADIST lesson, published 2019-06-19, was rechecked on October 19, 2026. The lesson explicitly labels WPS Office for Windows Personal. The publication date is evidence that the function was documented by that date, not its introduction date. Exact numeric builds, first and last supported versions remain unknown. The lesson does not establish retirement or deprecation, or parity across platforms and editions.

These are original documentation-based examples with independently calculated expected values. They were not executed in WPS. Vendor demonstrations are historical documentation, not our application tests. Display rounding, client precision and workbook interchange remain unverified; the extra digits in this guide are mathematical reference values. English function names and comma separators follow the lesson.

• EXP: evaluate the exponential in the closed-form checks.
• LN: work with logarithms in related model calculations.
• AVERAGE: summarize observations without fitting a gamma model.