BetaPERT Distribution

The BetaPERT distribution is a specialized version of the Beta distribution and is often used for project risk analysis. Mathematically, it is a Beta distribution. While a Generalized Beta Distribution requires four parameters, a BetaPERT requires only three. A particular formula (inherent to the BetaPERT) determines the mean of the distribution (and hence its shape).

By default, it is defined by specifying either a Minimum (0^th percentile), Most Likely and Maximum (100^th percentile):

Alternatively, if you check the 10% / 90% checkbox, you can specify the 10^th percentile, Most Likely and 90^th percentile.