Critical Path Method
▪ Scheduling and Project Management tool developed in the 1950’s
▪ Allow us to plan all tasks which must be completed in a project
▪ Aids time scheduling and resource planning
▪ They allow progress towards project goals to be tracked
Using the Critical Path Method
▪ Some activities cannot be started until previous activities have been completed
▪ Activities in a critical path method need to be completed in sequence
▪ These activities are known as sequential activities
▪ In addition to these, other tasks can be completed at any time
▪ These activities are known as non-dependent or parallel tasks
Drawing a CPM Chart: Step 1
• This can be done using a Work Breakdown Structure
• For each task state:
• The earliest start date
•The estimated time it will take
Drawing a CPM Chart: Step 2
Establish sequence by looking at:
• Which tasks should take place before this task happens.
• Which tasks should be completed at the same time as this task.
• Which tasks should happen immediately after this task.
Drawing a CPM Chart: Step 3
▪ Each circle/node should show a task within the project;
▪ Each circle/node should give start and finish times;
▪ Each circle/node should be numbered;
▪ The arrows/arcs should the sequence of the tasks;
▪ A description and duration of the task should be written under the arrows;
▪ Arrows should always run left to right
Drawing a CPM Chart: Step 4
▪ Determining the four parameters of each task in the network
Earliest start time (ES) - The earliest time an activity can start once the previous dependent
activities are over.
Earliest finish time (EF) - ES + activity duration.
Latest finish time (LF) - The latest time an activity can finish without delaying the project.
Latest start time (LS) - LF - activity duration.
▪ The float time for an activity is the time between the earliest (ES) and the latest (LS)
start time or between the earliest (EF) and latest (LF) finish times.
▪ During the float time, an activity can be delayed without delaying the project finish
▪ The activities in the critical path have an effect on the deadline of the project.
▪ If an activity of this path is delayed, the project will be delayed.
Benefits of the Critical Path Method
▪ Visual representation
▪ The project plan can be tested to ensure it is well thought out
▪ It identifies key tasks which could cause delays to the project if not completed
▪ It identifies tasks which could be delayed in order to complete other tasks which
are more time crucial
▪ It identifies the minimum amount of time a project will take to complete
▪ It identifies any project steps which can be completed faster in order to
complete the project on time
Disadvantages of Critical Path Method
▪ Can be more difficult to understand than Gantt Charts
▪ The time needed for tasks is not as clear as with Gantt Charts
More Information on Critical Path Method
This is a useful video which sums the information given in the slides and
will aid understanding of the critical path method
▪ Kelley, J. E. (1963). The critical-path method: Resources planning and
scheduling. Industrial scheduling, 347-365.
▪ Leach, L. P. (1999). Critical chain project management improves
project performance. Project Management Journal, 30, 39-51.
▪ Maylor, Project Management. Chapter 7
▪ Maylor, H., 2010. Project Management. 4th Ed. Chester: Pearson.
▪ MindTools, 2013. Critical Path Analysis and PERT Charts. [Online] Available at:
http://www.mindtools.com/critpath.html [Accessed on 07/11/13]
▪ Margaret Rouse, 2011. Critical Path Method (CPM). [Online] Available at:
▪ Tutorialspoint, 2013. Critical Path Method. [Online] Available at:
tm [Accessed on 07/11/13]