In project management, the “critical path” refers to a sequence of dependent or floating tasks that have to be completed in order to get the project done (according to the plan). People sometimes think that the tasks on the this “path” are the most important (or difficult or maybe expensive), the critical path only refers to time required to complete the tasks. You can identify a task being on the critical path if, delayed by one day, can influence the duration of the entire project.
In the Gantt Chart above, we have 5 tasks on the critical path (“Client meeting”, “Project report”, “Wireframing”, “Design” and “Front end development”). If any of these tasks is delayed by one day, the duration of the entire project will increase by one day (if the duration of the remaining tasks stays the same). The other two floating tasks (“Creating content” and “Architecture”) are not on the critical path because if they are delayed, they do not influence the duration of the entire project (they might become critical though if there’s a huge delay and their duration exceeds the duration of the entire project – a 7 or 6 day delay in this scenario).
The importance of the Critical Path
In the first place, the critical path is an indicator of the earliest date a project is planned to complete. When the critical path is highlighted, the project manager knows exactly what are the critical tasks he has to keep an eye on. When a delay occurs he has two options: automatically reschedule the remaining activities keeping their initial duration (this will result in delaying the whole project) or reduce the estimated time of one or multiple tasks in order to keep the initial project completion date.
There are some situations when lag is present between dependent tasks and this might change the way critical path is displayed.
In this case we have a sequence of tasks but the critical path is represented only by the “Front end development task”. Why so? The explanation is simple: there’s a one day lag between “Design” and “Front end development”. This means that precedent tasks are not considered critical (yet) because if there’s just a one day delay it won’t affect the end date of the entire project. If the “Design” task is delayed by one day though, and the lag is removed, the design task becomes critical, because any other delay will have an impact on the finishing date of the entire project.
Another scenario is when you specifically define the lag duration between two dependent tasks. In this case, the precedent tasks will be on the critical path too, because any delay of the precedent tasks will reflect on the finishing date of the project.
If the lag is longer than the one set by the project manager, the precedent tasks will appear as critical when the lag duration matches the one set by the manager.