The PERT Formula and Its Benefits

By using the PERT Formula combined with bottom-up estimating in project management, a savvy project manager can then determine the estimated completion date for a project. The way this date is calculated is by adding up the cumulative task durations that have been estimated utilizing the PERT Formula or other estimation methods. For more information on how this process works using Microsoft Project 2007, see Deanna's series, "Project 2007: Estimating Task Durations Using the PERT Formula."

...the PERT Formula can help determine what chance the project has of being completed by that date. If the date lies within the standard deviation of the formula, there is a better chance of completion by that date the closer the date is to the pessimistic estimated date, and a smaller probability for completion if the requested date is closer to the optimistic estimate for completion.

Items with a large range between the optimistic estimate and the pessimistic estimate for completion are flexible. Because of this, if a project manager needs to crash the project schedule or fast track the project schedule, the PERT formula can help them determine which action items contain this flexibility. In this case, the PERT Formula has a distinct advantage for project managers.

By estimating the time it will take to complete tasks using the PERT Formula and the Standard Deviation formula, project managers can schedule start and finish times for tasks in a more accurate manner. This is a great benefit, especially in complex projects where start and finish dates might not be clear. Using the task estimation method, the project manager would schedule all tasks due to their estimated completion time, and then use the start time of the first scheduled task and the end time of the final scheduled task as the start and finish dates of the project.