Critical Path Method (CPM)

Definition

Critical Path is the sequence of activities that must be completed on schedule for the entire project to be completed on schedule. This is the longest duration path through the work plan. The duration of the critical path determines the duration of the entire project. Each task/activity on the critical path is called a critical task. If a critical task is delayed by one day, then entire project will be delayed by one day (unless another critical task can be accelerated by one day).

The critical path may change from time to time as activities are completed ahead of or behind schedule. There may be more than one critical path depending on durations and work flow logic.

A related concept is the critical chain, which adds resource dependencies.

The Critical Path Method (CPM) is one of several related techniques for doing project planning. CPM is for projects that are made up of a number of individual "activities." If some of the activities require other activities to finish before they can start, then the project becomes a complex web of activities.

Critical Path Analysis is an effective and powerful method of assessing:

• What tasks must be carried out
• Where parallel activity can be performed
• The shortest time in which you can complete a project
• Resources needed to execute a project
• The sequence of activities, scheduling and timings involved
• Task priorities
• The most efficient way of shortening time on urgent projects
• How long your complex project will take to complete
• Which activities are "critical," meaning that they have to be done on time or else the whole project will take longer

If you put in information about the cost of each activity, and how much it costs to speed up each activity, CPM can help you figure out:

• whether you should try to speed up the project, and, if so,
• what is the least costly way to speed up the project.

An effective Critical Path Analysis can make the difference between success and failure on complex projects. It can be very useful for assessing the importance of problems faced during the implementation of the plan.

PERT is a variant of Critical Path Analysis that takes a more skeptical view of the time needed to complete each project stage.

Activities

An activity is a specific task. It gets something done. An activity can have these properties:

• names of any other activities that have to be completed before this one can start
• a projected normal time duration

If you want to do a speedup cost analysis, you also have to know these things about each activity:

• a cost to complete
• a shorter time to complete on a crash basis
• the higher cost of completing it on a crash basis

CPM analysis starts after you have figured out all the individual activities in your project.