Programme Evaluation and Review Techniques or PERT and Critical Path Method or CPM are the network techniques or models which are widely used in project management. These techniques are very useful for planning, scheduling and executing large-time bound projects which involve careful co-ordination of variety of complex and interrelated activities, estimating resource requirements and time for each activity and establishing inter-relationship amongst the activities. Scheduling requires the details of starting and finishing date times of each activity.

Generally we are always interested to know the important aspects of any project such as:

1. Expected completion time

2. Effect of any delay in any activity

3. How to use additional resources if projects are to be completed before time

4. Probability of completing the project in time

Programme Evaluation and Review Techniques (PERT) and CPM are two, popular quantitative analysis techniques that help managers to plan, schedule, monitor and control large and complex projects.


Prior to the development of PERT and CPM the most popular techniques for project scheduling was the Bar and Gantt chart. These charts show a graphic representation of work or a time scale. The main limitation of this technique is its inability to show the inter-relationship and inter dependencies among the many activities. To overcome such limitations PERT and CPM were proposed in the late 1950s.

PERT was developed in the 1950s by the U.S. Navy special projects office in co-operation with Booz, Allen and Hamiltan, a management consulting firm. It was directed at planning and controlling the Polarisis missile programme, a massive project which had 250 prime contractors and over 9000 subcontractors. Since then both these, assembly have been successfully applied to problems involving construction work, assembly line scheduling, maintenance operations, bid preparation submitting of project proposals, market penetration programmes, manpower planning etc. at about the same time in 1957 Critical Path Method (CPM) was developed by J.E. Kelly of Remington Raud and M.R. Walker of Dupont. CPM was used to assist in the building and maintenance of chemical plants at Dupont.

Critical Path Method (CPM)

It is observed that in a network one can enumerate many sequences of activities from starting event to end event. Each sequence will contain different combination of activities  with different duration. One of the important object to network analysis is to know the minimum possible time by which the project can be completed. This is done by determining the critical path i.e. the sequence of activities with longest duration. It is known as critical path because any delay in activities lying on this path would cause a delay in the whole project. To quicken the process, the activities lying on the critical path should be taken first.

The activities lying o non-critical path have some flexibility in their starting time and their extension or delay in start is not likely to affect the final completion date. These are known as Stack activities and should be given priority in order of their float value. Development of Critical Path Method (CPM) has provided a basis for more formal and general approach towards project management. This technique can be used situations where duration of various activities can be accurately visualized form path experience, CPM provides interrelationship among the elements of the project and identifies the relative importance of each in the overall schedule.


1. To determine a route between two or more operations which optimizes some measures of performance.

2. To locate the obstacles and difficulties involved in a production process.

3. To assign the starting and finishing times for each operation or activity.

4. To determine the float associated with each non-critical activity.


1. It is an important tool for effective project management.

2. It shows critical and non-critical activities in the project.

3. It estimates project completion time.

4. It is suitable for any project with interdependent activities.

5. It is the simplest form of network technique.

Steps involved in CPM

1. Calculate the time schedule for each activity

It involves the determination of the time by which an activity must begin and the time before which it must be completed. The time schedule data for each activity include the calculation of the earliest start, the earliest finish, the latest start, the latest finish times and the float.

2. Calculate the time schedule for the completion of the entire project

It involves the calculation of project completion time.

3. Identify the critical activities and find the critical path

Critical activities are the ones which must be started and completed on schedule or else the project may get delayed. The path containing these activities is the critical path and is the longest path in term of duration.

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