Key Critical Path Method Steps
The Critical Path Method (CPM) is a project scheduling method that breaks the project into tasks and depicts them in sequence. It lets you estimate the duration of each project activity and calculate the total duration of the project.
Crucially, it enables you to identify the critical activities–those activities that cannot be delayed if the project is to be completed on time. CPM helps you and your team know exactly what the critical tasks are, plan ahead timelines and contingencies, and, once the project is underway, compare planned progress with actual progress.
In this brief guide, we’ll take a closer look at the key steps in the Critical Path Method. Let’s get started.
Critical Path Method Steps
1. Identify Each Activity
Determine each higher-level task (the main deliverables) using a work breakdown structure. For this step, you can use outlines, tables, or lists.
Once you have listed the high-level tasks, break them down into subtasks.
Be specific but not overly detailed. Detailed activities can bog down your analysis of the critical path later on.
2. Define the Activity Sequence
During this step, you establish which activities depend on other activities to determine the order in which you need to complete them. This is the activity sequence and it’s an important step.
List the predecessors of each activity. A simple way to figure this out is to look at your list of higher-level tasks and ask yourself, “What task do I need to complete before this task can be completed?”
Some tasks can be finished at the same time as other tasks, while others can only be done after predecessor tasks are completed.
3. Create the Critical Path Analysis Chart
The critical path diagram is a network diagram or visual representation of the order of activities according to their dependencies.
Place each task in a square or rectangular box and draw an arrow from tasks that need to be completed before connected tasks can be completed in their turn.
While you can draw a critical path diagram by hand, it’s quicker and easier to use software to generate and edit it.
4. Estimate Completion Time for Activities
Depending on the scale of the project, you can estimate completion time in days or weeks. During this step, you’ll have to draw on your experience.
For safer estimates, you can use the three-point estimation method.
Come up with three estimates for every task including best-case estimate (a), most likely estimate (m), and worst-case estimate (b).
You can then use the Triangular Distribution formula in which E represents Estimate and 3 the standard method:
E = (a + m + b) / 3
Note: Alternatively, you can give more weight to the most likely value using the Weighted Average formula. In this formula, E stands for Estimate, and 4 and 6 the standard method to give the most likely value more weight. The formula is:
E = (a + 4m + b) / 6
5. Define the Critical Path
The simplest way to find the critical path is to look at your diagram and identify the longest sequence of activities on it—that is the critical path.
A more elaborate approach to defining the critical path is by using the Forward Pass and Backward Pass technique.
With this technique, you identify the earliest start and finish times and the latest start and finish times for each activity. CPM software simplifies this part of the process.
6. Update the Critical Path
You want to continue updating your critical analysis diagram as your project progresses. This way, you will be working with real completion times rather than estimates. And you will be able to tell whether you’re on track. More than that, you’ll be able to recalculate the critical path if necessary.
In the end, using the Critical Path Method becomes simpler if you use project management software that supports this method. After inputting your data, CPM software can identify the critical path with just one click.
Key Critical Path Method Steps – Summary
Here is a quick summary of the key critical path method steps in your project management plan:
- Identify Each Activity
- Define the Activity Sequence
- Create the Critical Path Analysis Chart
- Estimate Completion Time for Activities
- Define the Critical Path
- Update the Critical Path