A guide to using the critical path method

What is the critical path method? 

If your team is like most, you have several projects competing for attention with multiple contingencies and fixes looming on the horizon. The critical path method (CPM), or critical path analysis, is a technique for scheduling complex projects that was developed in the 1950s. The technique lets you identify the most important (or critical) activities and their dependencies to keep initiatives on track and on time.

What is the critical path in project management?

Project managers for all types of projects (software development, construction, manufacturing, engineering, etc.) use CPM to prioritize critical tasks, identify dependencies, and estimate the duration of each task. This lets them create more realistic schedules for completing the overall project.

The longest sequence of these critical tasks and their dependencies represents the critical path for the project. Other activities that are important to the project, but don’t have dependencies, can be completed out of sequence or in parallel with the critical path.

How does CPM differ from PERT?

The program evaluation and review technique (PERT) is another scheduling tool that was developed in the 1950s. Like CPM, PERT is used to identify the tasks needed to complete a project, but its focus is more on estimating the amount of time needed to complete each task and the overall minimum time needed to complete the entire project.

PERT estimates the time it takes to complete each task by using the weighted average of the most optimistic estimate (O), the most pessimistic (P), and the most likely (M).

The main difference is that PERT uses uncertainty to estimate task durations while CPM is used after durations have already been estimated. So you might see PERT being used in conjunction with CPM.

Why is it so important to define the critical path?

Any given project might have multiple processes comprised of multiple tasks. If you don’t identify the project’s critical path, you might spend too much time on side activities that could be completed at any time. This could cause delays that might jeopardize your project.

For example, let’s say you have the goal of getting to work on time. The process breakdown might be as simple as:

• Wake up early enough to get ready.

• Take a shower.

• Get dressed.

• Eat breakfast.

• Get to the train station.

• Get on the right train.

• Get off at the right stop.

Each task comes with its own process and set of tasks. For example, the getting dressed process might include putting on your shirt, pants, socks, and shoes.

These are the most important tasks you need to do so you leave your house clothed. These tasks do not need to be followed in a particular order. The only dependency seems to be that the socks need to be on before the shoes. 

In this process, you have allotted a certain amount of time for getting dressed. Some days you might get dressed faster than other days. This means you might have some extra time (slack or float) to work on a parallel task, such as putting on a belt, before you need to move to the next task.  

There might be other tasks associated with getting dressed, such as putting on a tie, a hat, or a jacket. These tasks can be completed during slack time or later in the process. For example, you might put on a tie as you ride the train. But if you spend too much time picking out a tie, you might have to skip breakfast.

So, identifying a critical path is important because it helps you to:

• Prioritize tasks: Identify the tasks that need the most attention to avoid any delays in your process.

• Identify slack: This is the total amount of time an activity can be delayed without affecting the entire project’s success.

• Efficiently manage resources: Mapping a critical path reveals where you have flexibility. This allows for more strategic resource allocation. You can assign more experienced team members to high-risk, critical path items to protect the timeline, while utilizing parallel tasks as lower-risk professional development opportunities for others. 

• Visualize dependencies: Diagramming your critical path and its parallel tasks lets you easily see where the dependencies are and what needs to be done when. 

• Plan for the future: Comparing expectations against actual project benchmarks provides a critical feedback loop. These insights allow you to identify recurring bottlenecks, enabling more accurate forecasting and risk mitigation for future projects.

How to find the critical path

You can find the critical path in any type of project using the following process.

Step 1: Identify all tasks and activities

Create a master list of all of the processes, tasks, and activities that need to be completed in your project. A reliable way to do this is with a work breakdown structure. This work breakdown structure template can help you break down a large project into smaller, more manageable processes and tasks to better understand dependencies and how individual elements contribute to the overall project vision.