EXPONDIST Function (LibreOffice Calc — Legacy)

• Introduced: Documented by LibreOffice 26.8.1.1; original introduction not established.
• Availability: Supported in LibreOffice 26.8.1.1, verified against its function registry. This identifies a supported release, not a final working version.
• Scope: Desktop Calc, using the English function name. Availability in other spreadsheet applications is separate.
• Checked: 2026-10-14 — function reference; versioned support. Documentation/source check; not a new native test. Existing example-specific test claims below retain their stated scope.

Quick answer: =EXPONDIST(0;0.5;1) has reference value 0.

EXPONDIST evaluates an exponential waiting-time model with positive rate λ. The density is λ×exp(−λX), and the lower-tail cumulative probability for X≥0 is 1−exp(−λX). The mean waiting time is 1/λ. Rate and mean are reciprocal parameters, so their units and roles must stay distinct. Pinned calculation logic.

=EXPONDIST(X; Rate; Cumulative)

Exactly three arguments are required. X is the waiting-time cutoff in a chosen unit. Rate must be strictly positive and use the reciprocal unit. Cumulative=0 selects density; a nonzero value selects the cumulative probability. For negative X the evaluator returns 0 in either mode. At X=0 the CDF is 0 and density equals Rate.

These eight formulas were recalculated through XLSX import in LibreOfficeDev 26.8.0.0.alpha0, build 2c87e51eeaa2b413ff4ae097b2705eea1995d8e5. Saved ODS values agree with independent high-precision references, rounded here to twelve decimal places. This is headless development-build evidence, not stable-release or GUI validation.

Suppose a model has mean waiting time 2 hours. Its rate is 0.5 per hour, so =EXPONDIST(2;0.5;TRUE()) gives approximately 0.632120558829, the chance of waiting at most 2 hours. Using 2 as Rate would describe a different mean of half an hour.

=EXPONDIST(2;0.5;FALSE()) returns density 0.183939720586 per hour. That is not an 18.39% probability of waiting exactly 2 hours; a continuous model assigns zero probability to one exact time. Label density columns with their units and probability columns as probabilities.

The chance of a wait between 1 and 3 hours is =EXPONDIST(3;0.5;TRUE())-EXPONDIST(1;0.5;TRUE()), approximately 0.383400499564. The survival probability beyond t is exp(−λt); for 2 hours it is approximately 0.367879441171.

For a desired cumulative probability p strictly between 0 and 1, the corresponding exponential cutoff is =-LN(1-p)/Rate. With p=0.9 and rate 0.5, the cutoff is approximately 4.605170185988 hours. The exponential model assumes a constant hazard; its memoryless property is a modeling assumption, not a fact established by the formula. A changing failure rate or arrival pattern needs a different model.

EXPONDIST and EXPON.DIST dispatch to the same evaluator in the pinned release. Both remain available. Choose a spelling that fits the workbook and exchange requirements rather than assuming that the older spelling is retired or inherently less accurate.

A zero or negative rate is rejected. A negative cutoff returns 0, while a positive rate above 1 can produce a density above 1 near zero; that does not violate the area-based probability interpretation. The numeric cumulative flag is zero-versus-nonzero, not a separate discrete count.

When changing hours to minutes, divide the rate by 60 as well as multiplying the time by 60 so λX is unchanged. For extremely small positive λX, the inspected cumulative branch computes 1−exp(−λX), which can lose digits through cancellation. The examples do not establish relative accuracy for such near-zero probabilities.

Development-build boundary checks

The following additional formulas were saved from the same headless import run. Error text is retained as an error, not converted to a successful zero result.

• EXPON.DIST
• EXP
• POISSON
• GAMMADIST

The LibreOffice 26.8.1.1 evaluator establishes the product-specific argument and domain rules. Mathematical references and composite examples were independently checked. Native evidence is limited to the eight reference formulas and listed diagnostics in the named development build. A deliberately stale SUM cache changed from 999999 to 3, and an uncached SUM returned 7 after forced recalculation. The earlier ordinary conversion failed the stale-cache control and was excluded. Composite explanatory calculations, stable releases, GUI entry and extreme-parameter accuracy were not established by this run.