Critical Path Description and Overview

Project team brainstorming at a whiteboard
••• GettyImages/ThomasBarwick

Critical Path is a term from the field of project management describing a set of tools and a methodology.

The technical definition of the critical path in a sequence of networked work packages is the path with the least amount of slack. In practical terms, this path is the sequence of events that if any are delayed, will delay the entire project. And in even simpler terms, the critical path is the sequence of tasks that will take the longest to complete to deliver the project. 

Critical Path Project Management describes a methodology for managing and controlling a project using a distinct set of tools. 

Identification of the Critical Path:

Project managers work with team members to define all of the work required to complete a project or to achieve the project scope. The work is typically broken down into units called work packages. These work packages are small enough in size that they can be associated with an owner, managed for risk and controlled for time, cost and materials.

Work packages that are too small are meaningless, and work packages that are too large provide no basis for effective management and control. A commonly described benchmark is that no work package should take less than eight hours to complete or more than eighty hours. It, of course, may vary depending upon the nature of the project. 

Each work team defines and estimates the duration and cost for their work packages. The project manager pools the work packages and sequences them in the order in which they must be completed. The estimates of duration and the sequence of events are used to construct a network diagram, where several key measures are identified. These include: 

  • Early Start: the earliest a work package can start. 
  • Early Finish: the earliest a work package can be completed.
  • Late Start: the latest a work package can be started and not delay the project.
  • Late Finish: the latest a work package can be finished and not delay the project.
  • Slack (Float): the amount of time a work package can be delayed and not impact the project.

These metrics are used to calculate the various paths through the network, producing a duration and identifying available slack for individual work packages. The project manager and project team members typically adjust the sequencing of the events and look at different options. Once resources are defined the work packages are sequenced yet again, looking for the most efficient, timely and least risky project plan. 

The project team can view the actual paths through the network, and the one (or more) that has the least amount of available slack (sometimes zero), meaning if any item on that path is delayed even by one day, the project will be delayed correspondingly. 

It is important to note the following:

  • There can be more than one critical path in a network diagram.
  • The critical path can change based on resource scheduling. 
  • The critical path can change during the execution of a project. 

Uses of the Critical Path:

The critical path is an important project management tool that allows the project manager and team to focus their efforts on the most important work packages. Common actions focused on the critical path include: 

  • Ensuring that resources are available when needed 
  • Borrowing resources from non-critical work packages to ensure completion of the critical items.
  • Careful monitoring and reporting for critical activities.
  • Smoothing or leveling of resources to most efficiently complete tasks on the critical path.
  • Crashing the schedule by adding resources to those items where the most cost-effective reduction in duration can be achieved. 
  • Identification of work that can be completed simultaneously (fast tracking) to ensure that there are no delays along the critical path. 
  • Use of the network diagram to assess the overall risk of the project. If the network has multiple critical paths or one critical path and several near-critical paths, it is said to be sensitive. The more sensitive a project network, the larger the risk of delays and the harder the job of the project manager and team for monitoring task completion. 

Computer Software and the Critical Path:

While very small projects lend themselves to a manual calculation of the critical path, for larger initiatives with thousands or tens of thousands of work packages, project managers rely on project management software programs to calculate and describe the project network diagram and critical path(s). Nonetheless, it is important that the project manager understands how to develop, refine and manage to the critical path. 


Updated by Art Petty