Critical Path Project Management (CPM)

A simplified example of critical path project management is this project plan for building a house. All the tasks in the project are listed in the Work Breakdown Structure (WBS), then the dependencies between the tasks are determined and the duration of each task is calculated.

Most project management software programs will calculate a critical path for you. This may be necessary if your project is complex. However, you can often determine the critical path yourself in simple cases.

Start with the earliest task, then determine which tasks can't start until that one is complete. The longest of these tasks is the next task in the critical path. Next, figure out what tasks depend on completion of that second task and the longest task among these becomes the third step in the critical path. Continue this process until you reach the end of the project.

The tasks, their dependencies, and durations are shown in the chart above. The critical path is outlined in red. Using this task list, you can see that the tasks that make up the critical path are 1, 2, 3, 4, 10, 11, 12, and 13. You'll have some extra time to complete the other tasks (5, 6, 7, 8, and 9) if necessary. This extra time is called "float." It's important to keep an eye on the other tasks, as well, because they could become critical path tasks if something happens to extend them.

If one of them slips and takes longer, the project timeline may be extended. For example, if the installation of insulation in task number eight is not properly supervised and is done in the wrong places first, it might make the installation of the electrical wiring (task number five), take longer. This places it on the critical path instead of task number four, making the entire project take longer.

You may be able to shorten the overall project timeline by compressing a task on the critical path. For example, task number four, installing the plumbing, is on the critical path. You can shorten that task by hiring another plumber or by having the scheduled plumber work overtime if you have the budget for it.  

Maximize your chances of completing your project on time by calculating the critical path and managing the tasks that make it up. Just remember that Critical Path Project Management can't be placed on auto-pilot. You need to make sure that no other task slips to point that it becomes a critical path task.