What is the Critical Path?

Phil De Gruchy

Jun 11 2020 5 min read

The activities in a project plan are driven by requirements gathered from the client and the agreed-upon scope of the project. While each task is important to the success of the project, not all are considered critical. The way that certain tasks are deemed critical is through a specific process and formula for calculating the shortest route through the project using the longest duration tasks. This route is called the Critical Path.

In summary, the tasks on the critical path are the ones that must be completed on time if the overall schedule of the project is not to slip. The key task details that are required for finding the critical path are:

Start Date
End Date
Duration
Dependencies

In this image, we see a project displayed using a Gantt chart with the critical path highlighted in red. Important information is being displayed about each individual task, it’s placement in the project, and how it is nested and related to other work. With the critical path highlighted in this way, it is easy to see which tasks are included on that path and which are not. The placement of a task on the critical path might influence how change is managed.

With these details established for every task, a project manager is able to map then calculate the total duration of the project. The project-wide implications of risks and issues are amplified when associated with critical tasks than with other tasks. If a delay or change occurs on a task that is not on the critical path, downstream impact is possible and will depend on the task’s successor relationships. However, a delay or change to a critical task will certainly have downstream impact on successor tasks and cause a delay or change to the project itself.

When tasks are late to start or finish, compressing the schedule is a way to get it back on track. We do this at the task level by either moving up a start date and working out of sequence or by adding more resources to complete the same amount of hours in a shorter duration. These schedule compression techniques are not limited to the Critical Path and can be applied to any task in the project, but risk or cost are likely to be increased as a direct result and schedule compression should be used with caution.

Managing changes on and off the critical path means the Triple Constraints are being impacted; schedule, scope, or cost. Decisions around how much additional cost is appropriate, how much schedule slippage is acceptable, or how scope must be cut to all require application of different techniques to manage those tasks. For critical path tasks, it becomes not a question of if changes will occur, but rather a question of the degree of changes required. Simply put, tasks on the Critical Path have the individual power to make or break project success. All tasks are important, but the Critical Path gives project managers more insight to individuate a response strategy.