# A to Z of Excel Functions: The NEGBINOMDIST Function

24 October 2022

*Welcome
back to our regular A to Z of Excel Functions blog. Today we look at the NEGBINOMDIST function. *

** **

**The
NEGBINOMDIST function**

In probability theory and statistics, the negative
binomial distribution is a discrete probability distribution that models the
number of successes in a sequence of **n **independent success / failure experiments, each of which yields success with
probability **p, **before a specified number of failures (denoted **r**) occur. For the record, a
success / failure experiment is also called a Bernoulli experiment or Bernoulli
trial.

You’re probably seeing the similarities between
this article and __the last one__. This function also returns the negative
binomial distribution, the probability that there will be a **number_f **failures before the **number_s**-th success, with **probability_s **probability of a success. The **NEG****BINOMDIST** function should be used in
problems with a fixed number of successes, when the outcomes of any trial are
only success or failure, when trials are independent and when the probability
of success is constant throughout the experiment. For example, **NEG****BINOMDIST** can calculate the probability that exactly two babies
born are male before one female baby is born.

The **NEG****BINOMDIST **function employs the following syntax to operate:

**NEGBINOMDIST(number_f,
number_s, probability_s)**

The **NEG****BINOMDIST **function has the following arguments:

**number_f:**this is required and represents the number of failures in trials**number_s:**this is also required. This is the threshold number of successes**probability_s:**again, this is required. This is the probability of success on each trial.

Unlike ** NEGBINOM.DIST**, this
function does not have the

**cumulative**argument.

It should be further noted that:

**number_f**and**number_s**are truncated to integers- if
**number_f**,**number_s**, or**probability_s**is / are non-numeric,**NEGBINOMDIST**returns the*#VALUE!*error value - if
**number_f**< 0 or**number_s**< 1,**NEGBINOMDIST**returns the*#NUM!*error value - if
**probability_s**< 0 or**probability_s**> 1,**NEGBINOMDIST**returns the*#NUM!*error value - the equation for the negative binomial distribution is:

where:

**x** is **number_f**, **r** is **number_s** and **p** is **probability_s**.

Please see my example below:

Essentially, **NEG****BINOMDIST **is a slightly
less flexible version of **NEGBINOM.DIST** and represents the version of the function used before its
successor was introduced in Excel 2010.
It is still recognised in Excel for legacy reasons. Although this function is still available for
backward compatibility, you should consider using the new functions from now
on, because this function may not be available in future versions of Excel.

* *

We’ll continue our A to Z of Excel Functions soon. Keep checking back – there’s a new blog post
every other business day.

*A full page of the function articles can be found **here.*