Difference Between CPM and PERT


There are many techniques for faster and more efficient completion of complex projects. CPM and PERT are two powerful tools to achieve this objective. There are similarities in the two techniques as they serve the same basic purpose. However, there are many differences that will be explained in this article for the benefit of those who may have doubts regarding their differences.

Due to complexity of projects, it is often difficult to eliminate time delays and cost overruns. However, if suitable techniques of planning, controlling and organizing are used, it is possible to reduce these cost overruns and project delays by a considerable margin. Problem with many tools lies in the cost of implementing and executing which makes them more of a liability than an asset. Such programs, because they require a large amount of reporting and monitoring far outweigh the benefits that accrue because of their use. These problems are very much done away with when a project manager uses either CPM or PERT. Let us see what these techniques stand for and how they differ.


There is high degree of uncertainty pertaining to completion time of certain activities. Particularly in research and development projects, it is difficult to gauge the time the project will take to complete. In such cases we can take probabilistic approach for each activity and define optimistic time estimate, most likely time estimate and pessimistic time estimate. With expected time for each activity, it is possible to determine the critical path. Thus PERT is a probabilistic tool that makes use of 3 estimates for completion of activities and is a tool for planning and control of time for completion of a project.


CPM on the other hand is a deterministic tool taking only a single estimate of time for completion of any activity in a project. It also allows for estimate of costs, thereby being a tool that can control both time as well as costs.

CPM vs PERT Summary

• Where the estimation of time for each activity is difficult such as R&D, PERT is a more suitable method

• In routine projects where estimated time for each activity is known, CPM is a better tool to control both time and cost.

• While PERT is probabilistic in nature, CPM is a deterministic tool.