Critical Path is a project scheduling technique that determines the shortest time that the current project plan can be completed.
When to use
Critical path is used when a project is schedule driven. In that case the critical path is the prioritization for project tasks. A critical path requires that a complete network diagram is developed with all tasks included and that each task has a duration estimate. With those two elements of project planning complete, the critical path can then be calculated.
Critical path is very useful when there are multiple parallel project paths. If the project is a sequential waterfall schedule, critical path provides no useful information since every task is critical. However, with multiple parallel paths, normally one path will be longer than all of the others – that is the critical path.
Critical path is often recalculated when project changes occur or if non-critical path tasks become very early or late to determine whether the critical path may have changed.
The critical path is the most important sequence of tasks for schedule-driven projects. A delay on the critical path immediately translates into a delay to the end of the project. The only way to shorten the time on a project is to shorten the critical path. Reducing time on any tasks that are not on the critical path will not impact the end date of the project.
I normally calculate the critical path when the planning for a phase is being completed. If the total time is longer than I had allocated for that phase, I investigate the tasks on the critical path and determine how they can be changed to shorten the duration (reduce scope, add resources, change task relationships). I also will increase the duration estimate of tasks with technical or resource risks that are on the critical path since a problem with that task immediately creates a schedule problem in addition to the technical or resource risk.
There can be multiple critical paths within a project – when that occurs, the overall schedule risk on the project is increased since either path could lead to a delay in the project completion.
Critical Path: “The sequence of activities that represents the longest path through a project, which determines the shortest possible duration.” PMBOK®Guide
This definition is taken from the Glossary of the Project Management Institute, A Guide to the Project Management Body of Knowledge, (PMBOK®Guide) – Fifth Edition, Project Management Institute, Inc., 2013.
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