The Excel EXPONDIST function returns the exponential distribution — useful for modelling the time between events. It is the legacy name of EXPON.DIST, introduced in Excel 2010.
Syntax
| Argument | Description | |
|---|---|---|
x | Required | The value of the function (a time or distance, must be ≥ 0). |
lambda | Required | The rate parameter of the distribution (must be > 0). |
cumulative | Required | TRUE for the cumulative distribution function; FALSE for the probability density function. |
How to use it
The exponential distribution models the waiting time until the next event in a process that happens at a constant average rate lambda. With cumulative set to TRUE you get the probability the event occurs by time x; with FALSE you get the density.
A rate of 10 means 10 events per unit time on average, so most waits are short — hence the high cumulative probability already by x = 0.2. It is common in reliability and queueing analysis.
Use EXPON.DIST instead: =EXPON.DIST(0.2,10,TRUE) in Excel 2010+ returns the same value with identical arguments. EXPONDIST remains only for backward compatibility.
Try it: interactive demo
Pick a EXPONDIST example to see the formula and its result.
Practice workbook
Frequently asked questions
What is the modern replacement for EXPONDIST?
EXPON.DIST, added in Excel 2010, with the same three arguments. =EXPON.DIST(0.2,10,TRUE) equals =EXPONDIST(0.2,10,TRUE).What does the cumulative argument control?
TRUE returns the cumulative distribution — the probability the event has occurred by time x. FALSE returns the probability density at x.What does lambda represent?
When is the exponential distribution used?
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