Difference Between Pert & CPM

by Mike Evans; Updated September 26, 2017

The program evaluation and review technique (PERT) and the critical path method (CPM) are project management techniques used to coordinate activities that contribute to the completion of a complex project. While they are similar, there are key differences relating to the amount of time each technique allocates to each task.

Core Difference

CPM is used for projects that assume deterministic activity times; the times at which each activity will be carried out are known. PERT, on the other hand, allows for stochastic activity times; the times at which each activity will be carried out are uncertain or varied. Because of this core difference, CPM and PERT are used in different contexts.


PERT is used for projects in which activity times are unknown. For example, take a research and development project (R&D). In an R&D project, the amount of time to complete a given task is unpredictable. In such a case, PERT is the best choice, since it allows planners to allocate three estimates for completion times – the most likely, the most optimistic and the most pessimistic.


The activities involved in a construction project, on the other hand, are much more predictable, and may not need three estimated completion times. If this is the case, CPM may be more appropriate, since unlike PERT, CPM also allows for planners to make trade-offs between the cost of the project and the amount of time needed to complete it.

About the Author

Mike Evans has written policies and press releases since 2008. He is particularly interested in writing on politics, law, ethics, church-state separation and science. Evans holds a Master of Arts in philosophy from York University and an Honors Bachelor of Arts with a double-major in philosophy and law and society.

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