Critical Path Method (CPM) in Project Management

The critical path method

The critical path method
The critical path method - CPM

The critical path method (CPM) is a project modeling technique developed in the late 1950s by Morgan R. Walker of DuPont and James E. Kelley Jr. of Remington Rand.[1]
According to The Project Management Body of Knowledge (PMBOK), The Critical Path is “the sequence of scheduled activities that determines the duration of the project.”
Briefly in this method, activities are listed, activity durations are determined, dependencies between the activities are established and the longest path is identified by making forward and backward calculations.

Critical Path

In a schedule network diagram, many paths can be seen starting from a point and ending at a point. These paths consist of activities which have durations and dependencies. Every path have some duration but the critical path is the longest path of the network diagram. In other words it is the shortest time possible to complete the project

Key Steps in the Critical Path Method

1. List the Activities
Activities can be determined by using the work breakdown structure and project scope.
2. Establish Dependencies
Predecessor and Successor activities should be determined in this step. Below questions should be answered;
Which activity will start before this activity ends?
Which activity will finish at the same time as this activity ?
Which activity will start after this activity ends?
3. Draw the Network Diagram
After the identification of activities and their dependencies, a network diagram can be drawn.

Critical Path Method-Network Diagram
Critical Path Method-Network Diagram

4. Estimate Activity Completion Time
Activity durations can be estimated by using past experiences, productivity analysis and three- point estimation method.
In three-point estimation, activity durations can be determined by making the estimations below;
– Most Likely Estimate: The most likely estimate
– Optimistic Estimate: The best-case estimate
– Pessimistic Estimate: The worst-case estimate

5. Identify the Critical Path

By the help of Forward Pass and Backward Pass calculations, The earliest start and finish dates, and the latest start and finish dates for each activity can be identified and The Critical Path of the network diagram can be determined.

Critical Path
Critical Path

Advantages of the Critical Path Method

The following are a few benefits of the critical path method:
– It is a visual technique which enables to show activities, activity dependencies and durations in the same diagram
– It enables to manage and organize large and complex projects
– It enables to calculate The Earliest Start/Finish and The Latest Start/Finish dates in order to manage activities and procurement tasks.
– It enables the project team to make time optimizations.

Disadvantages of the Critical Path Method

– It is hard to manage activities in large and complex projects without softwares.
– It does not consider resource allocations.
– Activity durations should be determined correctly orherwise, the critical path of the project will be wrong
– It will be hard to determine the critical path if there are many other similar duration paths in the project.


The critical path method (CPM) is a strong tool in project time management. It is used widely in project planning and updating phases by specialists. This method gives the project management teams correct completion dates of their projects.

[1] Kelley, James; Walker, Morgan. Critical-Path Planning and Scheduling. 1959 Proceedings of the Eastern Joint Computer Conference.


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