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What is the critical path method?

Simplify your worklife with the critical path method so you can ensure your project is always on time and on budget.


Critical path method explained

When you’re managing a complex project with lots of moving parts and evolving deadlines, it can be difficult to deliver on time and on budget. There are a broad range of project management tools that can help you achieve these goals, one of which is the critical path method (CPM).

So what is a critical path?

CPM is a project modeling technique that you can use to analyze, plan, and schedule complex projects. In essence, the critical path method requires you to list all the activities that need to be finished to complete a project, the length of time each activity will take, and the dependencies between these activities. The critical path itself is the longest amount of time it will take you to complete the overall project, giving you an insight into how best to structure your project schedule to ensure it’s delivered on time and at minimum cost. Put simply, the critical path method helps you to understand the optimum timeline for completing your project.

The history of critical path analysis

CPM was developed in the late 1950s by James E. Kelley of Remington Rand and Morgan R. Walker of DuPont. They were attempting to find ways to reduce the costs associated with plant shutdowns and restarts that were being caused by inefficient scheduling. By ensuring that the right tasks were performed at the right times, instead of simply saturating the problem with additional labor, they found that excess costs could be avoided.

Kelley and Walker published a paper on their research in 1959, although DuPont moved away from the technique after the management team that was responsible for it changed. Around the same time, the U.S. Navy and Booz Allen Hamilton developed a similar technique⁠—PERT (Program Evaluation and Review Technique)⁠—which is where the term “critical path” originated. In fact, critical path analysis had its roots in some DuPont techniques dating back to the early 1940s, where it contributed to the success of the Manhattan Project.

Although DuPont’s interest in the critical path method had diminished by the early 1960s, a couple of other companies began to use it to oversee large projects, including Mauchly Associates and Catalytic Construction. Initially, access to bulky, specialist mainframe computers was needed to use CPM. As a result, the cost of critical path project management was a significant barrier to entry. However, after the PC revolution and innovations in computer hardware/software made it possible to conduct schedule management on a standard desktop computer, usage of critical path became much more widespread.

How does critical path project management work?

The first stage of the critical path method has four basic steps. Here’s how they work in a little more detail:


  1. List all tasks/activities: First off, you’ll need to list all the tasks and activities that are necessary for the completion of the project in a Work Breakdown Structure (WBS). Generally speaking, this should only include critical tasks and higher-level activities (rather than granular detail), as it’s possible for critical path analysis to become too complex to manage if a detailed overview of all activities is included.

  2. Calculate duration of each task: Secondly, you’re going to need to calculate the longest time that each critical path task will need to be completed. Of course, an activity duration will need to be an estimate, so use your experience, as well as the knowledge of your colleagues, to make an informed guess. You’ll also need to list each task according to the earliest date that it can start and end without making the project late.

  3. Establish task dependencies: Next, you should collect any task dependencies, where a first activity or predecessor task determines the start date of the successor task. To work out your project’s dependent tasks, ask yourself the following questions when you’re listing activities:
    a. Which task needs to be completed before this task can begin?
    b. Which task should happen immediately after this task?
    c. Which task should finish at the same time as this task?

  4. Note project milestones: Finally, it’s important to make a note of major project milestones, as well as the project deliverables.

Once you’ve gathered all this data, you’ll need to construct a model to visualize your project activities. There are several different models that you can use, from simple graphs and network diagrams to Gantt chart views. Then, using this model, you can work out the critical path of the project itself. Just to refresh, that’s the longest path of your planned activities to the end of the project, as well as the earliest and latest dates/times that each activity can start without making the project late. This will also show you the longest duration of the project required for completion.

After you’ve worked out the critical path, you can identify which items are “critical activities” and which have “total float” (can be delayed without extending the project). You can then use this information for fast tracking the start times of certain tasks, shortening the project time if required, and manage resource constraints more effectively.

Advantages of the critical path method

There are several important benefits associated with critical path project management. First and foremost, it helps project managers identify the most important tasks within your project. If any of your critical path activities have a late start time or take more time than expected, the whole project will be affected. As such, it’s helpful for project managers to have a project plan that identifies which tasks need to be managed more closely than others. It’s also important to consider the fact that critical path analysis can help reduce project timelines. After you conduct your analysis, you’ll have visibility into the tasks that are best suited to duration reduction.

In addition, critical path project management can make the risk assessment process much easier. Once you’ve established task dependencies, it’s relatively simple to work out what the effect of a missed deadline is going to be on the next deliverable. Furthermore, critical path analysis provides project managers with the perfect framework to measure the actual progress of the project against the expected progress. By tracking your results against the original baseline, you can work out where the inefficiencies are and take steps to eliminate them from your workflow.

Is critical path right for me?

Critical path analysis can be used for virtually any type of project, including research, engineering, product development, software development, construction, and so on. If the following statements are true of the project that you’re embarking on, then the critical path method may be appropriate:

  • Activities are well-defined and when finished, will signal the completion of the project.
  • Activities are ordered and must be performed in sequence. For example, materials for a construction project need to be sourced before the actual construction can begin.
  • Activities can be stopped and started independently within a given sequence (counting out continuous-flow process activities like oil refining).

As you can see, critical path project management can be suitable for a broad range of industries and projects. But you don’t need to fully adopt critical path to benefit from its effects. If there’s an element of CPM that works for you, it may be beneficial to integrate that into your project management process. Ultimately, adaptability is one of the key qualities of a successful project manager.

Using critical path with your team

Now that you know a little more about the critical path method, it’s worth thinking about how you can make use of it within your organization. Dropbox offers a few tools that can help you implement critical path analysis. For example, Dropbox Paper can help you manage your whole project roadmap from one location, making it an ideal way to model critical path project management. First, use the project plan template to guide your team members through the project, every step of the way. Then, delegate tasks to the appropriate team members, create to-do lists to ensure your project moves along at an optimum pace, and use task management tools for a high-level perspective on your team’s assigned tasks. You can also present the critical path to your project team with tools like Dropbox Capture. Record yourself and your screen to clearly highlight critical activities, then share this with the team so they have a record to reference.

Final thoughts

Ultimately, the critical path method provides you with clarity, offering a visual depiction of your entire project workflow, from start to finish. By identifying the “critical path,” you can ensure that resources are allocated to the most important tasks and optimize the speed with which critical projects are completed and delivered.

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