# PERT Calculator

How much of a resource will be required to complete a project?

## What Is the PERT?

This formula, developed by the American Navy, was commonly used to estimate the time required for a task with several unknowns. There is no reason, however, that it can't also be used for estimating project costs - especially for projects in which time is a primary driver of project expense.

## Why Is it Important?

• There are many unknowns that can affect project execution times and associated costs. Many models simply ignore them, but PERT adjusts its output to account for them.

## Formula(s) to Calculate PERT

• ESTIMATE = (OPTIMISTIC ESTIMATE + (4 * MOST LIKELY ESTIMATE) + PESSIMISTIC ESTIMATE) / 6

## Common Mistakes

• Assuming that the optimistic and pessimistic estimates should be equidistant to the most likely estimate. Positive and negative risks are rarely equal.
• Not accurately identifying all positive and negative risks that can affect a project.
• Intentionally downplaying negative risks, due to political pressure.
• Using too little data to support the estimates used as inputs into the formula.

## Also Known As

• Program evaluation and review technique