Unlike traditional approaches to project management, the critical path method (CPM), also known as critical path analysis, makes use of algorithms to schedule tasks. Ensuring the timely completion of a project is an ever-present challenge, and the critical path method optimizes the process by turning it into a science. CPM sets its sights on determining the series of interconnected tasks that dictate the project’s minimum completion time, which is referred to as the critical path. This blog post will serve as a comprehensive guide to understanding and implementing the critical path method as well as juxtapose it with other scheduling and budgeting tools.
The Critical Path Method was a project-modeling technique introduced in the 1950s. Creators James Kelly Jr. of Remington Rand and Morgan Walker of DuPont developed it around the same time the program evaluation and review technique (PERT) rolled out of production. With CPM, they aimed to define a project by its bare necessities.
Although the CPM created in the late 1950s differs from the model in use today, it builds on the same principles. The critical path method was devised to calculate the longest path to project completion, which was determined through task categorization. This calculation was derived by reviewing the duration of each task, dependencies, and critical achievements. This trail of tasks determines the shortest time required for project completion. The deadline is reliant upon the tasks on the critical path. If any of these tasks took more time than estimated, the corresponding deadline would automatically be pushed back.
What Is Critical Path In Project Management?
Within project management, a critical path is referred to as an uninterrupted sequence of tasks interdependent on each other that dictates and defines the minimum possible completion date for a project. The project timeline hinges on the links created by this path, if one link is weakened or not delivered on time, it will affect the entire schedule.
The critical path method offers a structured approach to project scheduling and analysis. Following are some of the ways in which project managers and teams can benefit from the said analysis:
As mentioned above, the critical path method basically offers managers an algorithm to streamline the scheduling process. CPM uses a variety of specific calculations to identify the critical path. To explain the formula in simple terms, we can break the core concept down into two main steps, namely the forward and backward pass.
Forward Pass
The forward step involves calculating the earliest possible start time, i.e., the ES, and the earliest possible finish time, the EF. Consider the possible dependencies between all tasks. In case of the forward pass, managers must assume all predecessor tasks (tasks that need to be completed before another can begin) begin at their ES.
Assuming all predecessor tasks have been completed at their EF, the forward pass then calculates the earliest time the upcoming tasks can potentially begin. This calculation is done with consideration of all task dependencies.
Backward Pass
The backward pass, inversely, calculates the latest a task can start, the LS, and the latest it can finish, the LF, given that the project completion date remains unchanged. In order to calculate these two quantities, the backward pass works backwards from the project deadline whilst keeping all dependencies under consideration. It works under a simple formula of subtracting the duration of a task from the project due date.
Managers can mediate on a critical path by comparing the earliest and latest allowable start and finish times calculated in both passes. Tasks with no affordable slack (the difference between the latest allowable start time and the earliest possible start time) constitute the critical path. The tasks with a float time (delays that can be made without affecting the total project time) will constitute the non-critical path and are called sub-critical.
Finding a project’s critical path can be done in two ways; manual calculation or using a project management software. Each method offers its own steps for calculating a critical path.
Manual calculations fare better for small-scale projects, ones that do not have a long list of task dependencies. This method begins with first calculating the forward and backward pass for each task. This is followed by identifying the slack allowed in total. Slack and buffer essentially mean the same thing and can be used interchangeably to represent the time a task can be delayed without an overall impact on the deadline. Tasks that have zero slack are determined to be the critical path.
Project management software with built-in CPM schedule functionality automate the forward and backward pass calculations, streamlining the critical analysis. Users simply have to input their project tasks, their dependencies, and an estimated duration into the software. The CPM software will then visually represent this information.
Though similar, CPM and PERT differ in their core focuses, time estimates, and project suitability. Where CPM is more concerned with calculating the minimum duration of a project and the specific sequence of tasks responsible for this timeline, PERT factors the inherent variability of project task durations and focuses on providing three time estimates for each task. While CPM takes a deterministic view, regarding what has been discussed as set in stone, PERT favors a probabilistic view. This is to say that PERT takes into account the probability of there being three different timelines
CPM is suitable, therefore, for projects that follow a path schedule and have well-defined tasks with predictable durations. PERT is ideal for projects that require flexibility and deal with a lot of variables.
CPM and Gantt charts must not be thought of as interchangeable. They are complementary tools rather than replacements for each other. Although Gantt Charts can display a critical path, it does not have the capacity to calculate it the way CPM does. Where the critical path method offers the analysis, Gantt Charts provide visual representation and progress tracking of said analysis.
A Gantt chart is a popular visual tool for scheduling tasks and tracking project progress. While a Gantt chart can display the critical path, it doesn't explicitly calculate it like CPM does. CPM provides a more in-depth analysis of task dependencies and allows for what-if scenario modeling to assess the impact of potential delays.
Consider having to launch a social media campaign for an upcoming product release. Here is an example of how you might use CPM:
- List the Tasks – Tasks for a campaign may include video development and marketing materials, i.e., images, billboards, or social media posts. Further tasks include shooting footage, securing partnerships and deals, launching paid advertisements, scheduling social media posts, and monitoring campaign performance
- Identify the Dependencies – Materials need to be procured before shooting can begin. There needs to be an official shoot before social media posts can be scheduled. Partnerships need to be secured before launching a paid campaign. Lastly, monitoring responses to the campaign may also influence posts on social media
Using the Critical Path Method will help you organize all relevant information in relation to each other and map out the most efficient way to tackle tasks. Knowing which tasks are critical and which have room for delays streamlines decision-making and reduces confusion in prioritizing where to start. Effectively using CPA can boost your project management capabilities and contribute in your journey toward project success.
