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Brief Overview of PERT

For those of you interested in learning more about the statistical tool used in project management, Program Evaluation and Review Technique (PERT), please see the below information on how to calculate a project’s duration and its shortcomings. For the algebraic representations and formulas please see the attached PDF handout (PERT Presentation Handout). For an example using the Startup Project, please see the attached excel document. Both documents are available under “Downloads” at the bottom of this page.

  1. For each task in a project, we identify :
  • a- minimum duration
  • b- most likely duration
  • c - maximum duration
  1. Calculate mean and variance of each task’s duration

  2. Identify project’s critical path.

  3. Calculate the project’s mean by summing up expected durations of critical path tasks.

  4. Calculate the project’s variance by summing up the variances of critical path tasks.

  5. Assume that the project’s overall duration follows a normal distribution with mean and variance.

  6. Calculate the chance of completing the project by time T using the normal distribution.


Critical Path

  • may be several (near-) critical paths
  • may differ from what was initially expected
  • may change during project execution

Assumes tasks’ durations are independent

However, a project delay will often affect many activities simultaneously: for instance, weather delays in construction projects, new technology failure in project development, cash flow problems in business start-up, etc.

Project duration might not be Normally distributed

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This article is from the free online course:

Fundamentals of Project Planning and Management

Darden School of Business, University of Virginia