EXPONDIST Function (OpenOffice Calc)

• Introduced: First release not established; documented by OpenOffice.org 3.3.
• Supported in: Apache OpenOffice 4.1.16; this is not a final supported version.
• Scope: Desktop Calc with English semicolon-separated formulas. Locale and other-product contracts may differ.
• Checked: October 14, 2026. Eight reference formulas and 1 boundary case were recalculated in Apache OpenOffice 4.1.16 on Linux x86-64, Build 9816 after XLSX import; other explanatory calculations are independent references.

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. Release implementation.

=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.

Values below are rounded to twelve decimal places. These eight formulas were also recalculated in Apache OpenOffice 4.1.16 on Linux x86-64, Build 9816 after XLSX import. Saved results agree with the independent references to the checked precision.

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.

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.

Observed boundary checks

These additional cases were saved from the same 4.1.16 import session. Error displays are errors even where the ODS numeric attribute is zero.

• Function-specific official evidence
• Pinned evaluator and domain checks

The saved import workbook retained the stated formula identities. A deliberately stale SUM cache became 3 and an uncached SUM became 7, confirming recalculation. The observed scope is the named release and method only; explanatory composite formulas are independently calculated unless specifically listed among the native cases. Other releases, locales and extreme-value limits were not established by these ordinary examples.