Critical Path Method (CPM)

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by StarAgile

December 22, 2020
Category Project Management


Critical Path in Project Management

What is Critical Path?

Managing project can be accomplished by various tools for a successful completion. There is a key project modeling technique to accomplish the project deliverables. It is the longest path that is required to complete the tasks with their duration for a project. It is also the longest path from the start of the project to the finish of the project. It provides you the actual schedule of the project considering all the tasks with their durations. We call that as Critical Path Method/CPM.

CPM method can be done by doing it manually or by using softwares.

Typically both PERT and CPM are used in the projects to determine the project schedule and the tasks with duration to accomplish the deliverables. CPM is discussed in detail with hands-on and by taking real-world examples in the PMP certification training online conducted by StarAgile institute.

What are the Critical Path and common terms used? 

There are important terms to consider while doing CPM. 

Earliest Start Date - You need to first know what are the dependencies for this task and also the constraints for the start date.

Earliest Finish Date - This is nothing but the earliest date by which any tasks can be finished after considering the constraints and the dependencies.

Latest Start Date - Knowing when the project needs to be finished as per the schedule and working backward from the date of finish you arrive at this date. Extending this date may cause the project schedule may become upset.

Latest finish date - You need to evaluate the latest finish date after which the schedule can be upset or the project may be extended causing the project to miss the deadline.

Float - This is also called a slack period it describes how long you can delay the tasks before which it crashes the schedule of the projects and causing to miss the deadline. Remember the critical path has zero floats.

Crash duration - This describes the shortest quantity of time a task can be scheduled. This can be done by adding more resources and decrease the time needed to finish the task. It mainly depends on the cost and time constraints.

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Advantages of Critical Path Method in Project Management

The advantages of CPM are as follows,

• It is a great visualization tool that helps to know the key tasks, dependencies, and constraints and helps to plan the project schedule.

• It is a great tool to identify the critical and non-critical tool

• It helps to set the milestones and key deadlines for each task and project.

• It saves time and helps in the management of the project.

• It provides the real-time status of the project and helps in tracking progress

• It helps in evaluating the project's timeline

• It helps in identifying the critical activities that need attention

• It makes the dependencies transparent and clear.

• Finally, it ensures you know the critical path or longest path to accomplish the project completion.

Project Critical Path Analysis and CPM Project Management

By mapping the tasks with duration and the estimated time you can do the critical path analysis. This includes mapping out the dependencies of resources and tasks and knowing the cost and time constraints to finish each task.

The necessary rules for the critical path analysis are as follows,

• It makes clear the task dependencies on other tasks for their timely completion.

• It maps the duration of each task with the earliest and latest finish and starts dates.

• It is also helpful in making the appropriate decision on the constraints such as time, cost, and scope.

• By understanding the dependencies of every task we will know and set the realistic deadline for the projects.

• Critical Path Analysis is generally used in a complex and large project where there are a lot of tasks and helps in making complex and informed decisions.

CPA was first used in 1950 by Morgan Walker of DuPont and James Kelley of Remington Rand also called a critical path method. The first version of this was used in the Manhattan project a secret project to develop an atomic bomb to end World War 2.

It is used to identify the dependencies used to map the tasks from start to finish. It is also needed to find out the critical tasks and non-critical tasks to focus on the critical tasks first and prioritize the tasks to complete the project successfully. 

The critical path method represents the understanding of the risks and bottlenecks in completing the tasks as there may be some tasks that are dependent on other tasks completion before which it cannot start.

To arrive at the reasonable deadline date the tasks can have slack time or float and CPM is used to calculate the critical and non-critical tasks with the maximum and minimum amount of time the tasks can be completed. The timeline in CPA can be used in the Gantt chart to map the key dependencies of the projects. The project plan is tracked in CPA to ensure that there are no needs for any adjustments and if the adjustments are needed can be made in the CPA and updated in the project plan.  

How to find the Critical Path - Critical Path Method Examples 

The following are the steps to use the critical path method.

• Identify the requirements of the project.

• Break down the requirements of the project into tasks.

• Estimate the duration of each task.

• Create a CPM network diagram.

• Create a Gantt chart or bar chart.

• Perform resource-leveling.

• Adjust the schedule or compress it if required.

CPM Example

There are four elements in the CPM let us see the example.

First is Critical Path Analysis - This is represented in the following diagram.

 

Now from the diagram, we can evaluate the critical path    

Start >Activity1 > Activity3 >Activity4 > Finish

Start > Activity2 >Activity3 >Activity4 >Finish  > Critical Path

Start >Activity2 >Activity5 >Finish

Float determination – Here the critical path will have zero floats and to calculate the float of the other tasks is very easy which is to subtract duration from the duration of the critical path do this for all the paths.

For Example


Early Start, Early Finish and Latest Start, Latest Finish – Read the diagram carefully,


To calculate the Early Start and Early Finish consider the forward pass beginning with the first activity.

In this case, the ES of acitvity1 is one. EF is ES+duration-1.

For activity3 The ES is EF+1 and ES is 5+1 = 6

If the activity has more than 1 predecessor you will consider the largest of the EF.

Similarly,

To calculate the Late Start and Late Finish consider the backward pass. That is beginning with the last activity.

The late finish for the last activity is the same as the Last activity's EF in the critical path. The LS is the LF-duration+1

For activity 4 in the critical path, the LF is the same as EF and LS is LF-duration+1

For activity3 in the critical path, the LF is activity 4 LS-1. Activity3 LS is LF-duration+1.

Conclusion

StarAgile institute conducts project management certification that covers the CPM tool method in detail. StarAgile is the training partner for Project Management Institute (PMI) in conducting the online PMP training. Register now for PMP training at StarAgile and lift your career to new heights.