Smartsheet Contributor Kate Eby
The critical path method (CPM) is a scheduling technique that project managers use to determine the minimum duration and level of flexibility in a project. Learn how to identify critical activities and find insight from experts in our guide. Included on this page, you’ll find steps for identifying critical activities and visual examples of critical vs. non-critical activities. Plus, you’ll learn about crashing activities in CPM.
A critical path in project management is the longest possible sequence of dependent tasks that stakeholders must complete on time in order to deliver a project on schedule. By identifying the critical path, you can determine the earliest project completion date. Essentially, locating the longest sequence of dependencies allows you to find the shortest project duration. Read our guide to the critical path method to learn more about this practice. “Critical activities are those that will delay the overall project duration, whereas non-critical activities won't delay a project,” said Thomas Jepsen, CEO of home-building platform Passion Plans. “Because of the nature of non-critical activities, you are more free to choose when to start a non-critical activity.”
A critical activity in project management is any task that stakeholders must complete on schedule to meet project deadlines. Delays in one activity will affect subsequent tasks and the entire project unless you can reduce the time on other tasks. The terms critical activity and critical task are often used interchangeably in project management. There are two types of critical activities:
The concept of resource constraints, or the limitations on resources you have available for a certain project, is important to understanding critical activity and critical path. Examples of resource constraints include staff hours, budget, equipment, and supplies. More resource constraints result in more dependencies, which lengthen the critical path. Suppose you’re hosting a dinner party without any assistance. If you’re preparing a main course and a dessert that will each take an hour and you can make only one dish at a time, these tasks become dependencies because they’re constrained by your time. The availability of your kitchen equipment may be another constraint. But if you enlist a friend to bring dessert, you turn the two responsibilities into parallel tasks. By reducing the constraints on time and kitchen space, you’ve shortened the critical path.
Critical path activities are often important because they can throw the entire project off schedule. The key distinction between critical vs. non-critical activities is whether a late start or finish will push back the project completion date. For example, a task may be an important part of a project, but it isn’t considered a critical activity unless completing it late will delay the entire project.
Most projects include both dependent and parallel tasks. To develop a schedule, project managers typically identify the following for each activity:
Project managers assign each task a float (also referred to as slack), which is the amount of time the task can be delayed without impacting the project schedule. Activities on the critical path will have zero float. CPM works best when there’s a high level of certainty about how long critical path activities will take to complete. When project managers aren’t sure of the duration of some tasks, they’ll often use CPM in tandem with the project analysis and review technique (PERT), another approach to project management. In PERT, you calculate three durations: the optimistic duration, the most likely duration, and the pessimistic duration. Using a weighted average of the three durations, PERT creates an estimated duration.
Before you apply the critical path method, you’ll need to have a well-defined project scope. Use a critical path tracking template to help you plan and adjust the project schedule. Once you’ve established the goals, budget, and schedule, these following six steps can help you find critical activities in CPM:
Seek feedback when scheduling tasks using CPM. “Reviewing your critical activities with key stakeholders is crucial,” says Jepsen. “While the underlying ideas may be rather simple to follow in a diagram, it's important to understand that you're working with human beings. In the real world, you're operating in a dynamic situation where initial project detail assumption may not hold. Perhaps your main engineer falls sick. What do you do then?”
These examples demonstrate easy visual examples of critical path activities/tasks versus non-critical path activities/tasks. We’ve broken out the tasks that must happen in a particular sequence (critical) vs. those that don’t (non-critical). Example #1: Baking a Birthday Cake Critical activities:
Non-critical activities:
A: Mixing the batter B: Pouring the batter into the pan C: Preheating the oven for 15 minutes D: Baking the cake for 20 minutes E: Making the frosting F: Counting the candles G: Frosting the cake H: Adding and lighting the candles The critical path for baking a cake is A, B, D, G, H. Example #2: Publishing a Book Critical activities:
Non-critical activities:
The critical path for publishing a book is A, B, D, G, H. Example #3: Building a Website Critical activities:
Non-critical activities:
The critical path for building a website is A, B, C, F, G, I.
A crashing activity in critical path management is a strategy of adding resources to an activity, potentially resulting in a new critical path. Project managers may use crashing to speed up the timeline or when a project is behind schedule. For example, if a storm delays a critical task in a construction project, you may crash an activity by hiring additional contractors, reallocating staff who are working on a different activity or project, or paying overtime to stay on schedule. An alternative to project crashing is fast tracking, in which the team completes activities in parallel. Project managers typically use crashing after fast tracking has failed.
A project’s critical activities are those that have zero float, meaning any delay in completion delays the entire project. In contrast, the critical path maps the longest path through all critical activities from start to finish in a project. Returning to the cake-baking example, mixing the cake batter and baking the cake are activities with zero float. Any delay in either task would delay the completion of the cake. For a real-world example in project management, suppose you are obtaining permits for a construction project. You need to obtain permits to begin site work, so if permitting takes longer than you expected, the entire project schedule will be thrown off track. As an example of critical activities, say you are planning an event budget. Until you make the budget, you can’t book a venue, sign contracts with vendors, or market the event.
A critical task in project management is an activity that must be completed on schedule to avoid delaying a project. This is the same as a critical activity.
A critical flag is a mark applied to tasks that you deem critical using project management software. You can apply a critical flag to a task if it affects the duration of the overall project. Otherwise, the task is considered non-critical.
Apply a critical flag to any task with a total float of zero or a negative float, which occurs when a task’s schedule must be compressed in order to complete the project on time. Project managers will often create multiple critical paths during a project because delays may make tasks that were originally non-critical activities into critical activities. It’s essential that you closely monitor critical tasks, along with any linked non-critical tasks that are at risk of becoming critical.
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