Time Management: How to Determine the Critical Path

4/12/2012 Carsten Howitz Project Management

Critical Path in Time Management

You may have heard about the critical path in a project and how the development of the project schedule is dependent on the critical path. As a project manager the critical path is essential to determine potential issues in our project schedule.

So what is the critical path and how do we determine it? Well, let’s first take a look at a network logic diagram for a simple sample project.

Each activity has a duration measured in weeks and the arrows show how each activity is depending on other activities to finish before they can start themselves. In the sample activity: A must finish before C can start and D can only start once C has finished etc. We can also see that activity C can only start once both A and B has finished.

From the diagram we can determine three separate paths:

Start – A – C – D – Finish: 8 weeks
Start – B – C – D – Finish: 9 weeks
Start – B – E – F – Finish: 7 weeks

The critical path is defined as the longest path in the diagram and in our example it is path B-C-D, which is the critical path of 9 weeks. What’s so critical about it? If one of the activities on the critical path is delayed the entire project is delayed!

If for instance activity D is delayed 1 week, the project will be delayed with 1 week.

But if activity E is delayed 1 week it will not delay the project because path E is on will just be 8 weeks and still be done one week ahead of the BCD path.

So the critical path is made up of activities that cannot be delayed without delaying the finish of the entire project.

What happens if activity E suddenly is delayed 3 weeks? In that case the B-E-F path becomes the new critical path of 10 weeks and the finish of the project is delayed. The project manager must now determine how to handle this delay or accept it as the new critical path.

Will a project only have one critical path? A project can easily have more than one critical path and in that case the project manager must know all of them.

So now that we know what the critical path is and how we determine it; how do we use it practically when managing a project?

We use it to determine if the project will be delayed if an activity is delayed. If the activity is on any critical path the answer is Yes! If not, it depends on if the delay makes the activity create a new critical path. If not, the answer is No!

Projects usually have hundreds of activities and much more complex dependencies than our example. So project managers usually use software to set up the activities and dependencies and let the software calculate the critical path(s). If an activity is delayed the project manager can enter the delay in the software and see how it affects the overall finish of the project. It the project is delayed, the project manager can use the software to rearrange activities, dependencies or suggest additional activities as needed to bring the project back on track.

The critical path is critical to the Time Management knowledge area. Make sure you know how to use it correctly next time you manage a project.

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