What is a Critical Path?
CPM is a mathematically based algorithm for scheduling a set of project activities, and is now included in Project Gantt 2013.
Using these tasks times and requirements, CPM calculates the longest path of planned activities to the end of the project, and the earliest and latest points that each activity can start and finish without making the project longer. This process determines which activities are “critical” (i.e., on the longest path) and which have “total float” (i.e., can be delayed without making the project longer).
You can see this working in the example below, with the critical tasks Reak, track3, lastly and Dev backend all highlighted as being critical.This also highlights how not just one path is identified, but also the task that uses resources that can impact other tasks is also highlighted. So here, Dev backend requires John, but track3 starting straight after it also requires John. So any delays in Dev backend will impact John, track3, and delay the project.
As shown above, the critical path consists of the longest sequence of activities from project start to end that should be started and completed exactly as scheduled to ensure the project is completed by a certain date in the future. If jobs on the critical path slip, immediate action should be taken to get the project back on schedule. Otherwise, completion of the whole project will slip. Imagine that you have a project that will take 300 days to complete. If the first activity on the critical path is one day late, the project will take 301 days to complete, unless another activity on the critical path can be completed one day earlier. So the critical path is simply all the tasks that determine the end date in your project schedule.