PMI defines projects as “A Temporary endeavor undertaken to create unique products, services, or results.” The term “temporary” highlights that projects have a definite start and end date. Do you know there are specific project management tools and techniques that help project managers monitor the project timeline? The Critical Path Method is one such tool.
As a project manager, you must constantly be aware of all the project management methodologies and associated tools and techniques. In this blog, we cover the critical path method in detail. By the end of this blog, you will have a solid understanding of the key concepts of the critical path method and the process of using the CPM.
What is the Critical Path Method in Project Management?
The Critical Path Method (CPM) is a project management technique that outlines all the tasks necessary to complete a project. The outlined data is used to track the longest series of dependent tasks and the time it will take to finish them. CPM can be said to be a quantitative tool for decision-making related to scheduling.
CPM emerged in the 1950s as a way to solve scheduling problems in complex projects. James E. Kelly and Morgan R. Walker are credited with its development, driven by the need to create a more efficient and time-focused approach to managing projects. In their article “The Origins of CPM,” they mention how CPM came from a very honest place of wanting to do things the better way.
Determining an activity/event is critical in terms of its effect on the total time duration of project completion is the core principle of the Critical path method. Which means delaying that critical path is not possible. CPM provides a perspective on how best to schedule the activities to make it cost-effective and get a target date for project completion.
CPM gives project managers managing complex projects the analytical tools to determine the shortest duration possible to complete the project. It shows which activities should be completed absolutely on time to avoid the overall project delay.
Key Concepts of Critical Path Method (CPM)
Time is the ultimate constraint in effective project management. Delays, scheduling issues, and bottlenecks can turn most ambitious projects into a logistical nightmare. Critical path method offers a structured approach to ambiguities linked to project scheduling. To understand how CPM functions in the project management field, it is necessary to understand the key concepts that direct it.
Listed below are some of the primary concepts that govern the critical path method.
Critical Path
The critical path is the longest sequence of dependent activities or tasks that must be completed to finish the project on time. It tries to follow the shortest time duration route for the same. Any delay in the critical path will certainly lead to a delay in the project.
To illustrate, consider a project with multiple tasks. Some of the tasks depend on others to be completed first. Now, the critical path consists of all the dependent activities that will take longer to complete. Any delay on one of those tasks will push back the entire project.
Float
Slack or float refers to the time duration for which an activity can be delayed before it hampers any dependent tasks of the project. There are two types of float as stated below:
- Free Float: The amount of time a task can be delayed without affecting the start time of any dependent tasks.
- Total Float: The amount of time a task can be delayed without affecting the project’s finish date.
You need to understand the concept of Float as it acts as a buffer zone between consecutive activities. It is especially useful for tasks that are not part of the critical path. Float proves useful in situations when projects are facing unexpected challenges and helps in avoiding derailing the tasks on the critical path.
Dependencies
Almost all tasks in projects are interdependent, meaning that for one task to get started, the other one must be completed. The items on the dependencies list are an important factor in devising the entire project structure in terms of scheduling. Project managers commonly use the following task dependency terms in the project management field:
(We will use symbols A and B as two tasks dependent on each other to illustrate the mentioned task dependencies below)
- Finish to Start: In this case, Task A must be complete for Task B to start.
- Start to Start: Task A and Task B should start at the same time.
- Start to Finish: Task B cannot be completed unless Task A starts.
- Finish to Finish: Task B will get completed only if Task A is completed.
Activity Duration
All the Tasks or Activities to be done for a project to get completed, require a definite amount of time. The exact estimation of each task’s duration is a crucial component of CPM Project Management. To determine the activity duration, assess resource availability, task complexity, and potential challenges that may affect the timeline. While estimating activity duration and accounting for dependencies, you can schedule projects for timely completion.
Steps in CPM Project Management
You can learn a lot about the concepts and theories that shape them. But to understand the working of these concepts, you need to understand what steps they follow along with the purpose of these steps and the expected results. The process in CPM Project Management follows standard steps that ensure that the concept of the critical path method is in place to guide the entire process till the project completion.
In this section, we will provide a brief overview of the steps involved in CPM Project Management.
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Identify/Define All the Tasks To Be Done
The first step in CPM is to break down the project into all its tasks/activities. These tasks should be detailed enough to be clearly understood and measured. At this step, the project managers should focus on capturing everything that needs to be done to meet the project’s objectives. Breaking down a project into clear tasks is essential for effective scheduling. A Work Breakdown Structure (WBS) simplifies this process by organizing tasks systematically. Learn more about WBS in our detailed blog.
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Set The Task In Order of Their Sequence
The next step is to get all the tasks in order and in their sequence. In this phase, you need to identify which tasks are dependent on others. Afterwards, arrange the sequence in a way that avoids any miscommunication or miscalculation. Organizing the task into a logical order is essential for creating a workable schedule and ultimately a clear project path.
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Estimate Duration of Each Task
One of the important steps in the CPM process is the correct estimation of each task duration. At this stage, consider things like resources, availability, complexity, and potential risks. The more accurate the time estimation is the better the chances of getting the project timeline right.
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Make The Project Network Diagram
The Project Network Diagram is an essential metric in CPM Project Management. Once you identify, organize, and schedule all tasks, the next step is to create the project network diagram. This visual representation consists of all the tasks, their interdependencies, and their respective sequences. The focal point of this diagram is to easily identify and monitor the critical path.
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Define The Critical Path
Once the network diagram is in place, it guides the process of identifying the critical path. The critical path is the longest path of dependent tasks that determines the shortest possible time for completing the project. It is necessary to recognize and define the critical path, as any delay in the task on this path can affect the project finish date.
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Calculate Project Duration & Float
With all the calculations sorted out, calculate the entire project duration. Afterwards, calculate the float (or slack) for non-critical tasks. Understanding float helps in managing resources more flexibly and mitigating risks if delays occur.
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Monitor the Critical Path
After the project starts, it is important to constantly monitor the critical path. Project managers should track the progress of each task and ensure timely completion of tasks on the critical path. If there are delays in any tasks, address them immediately and make necessary adjustments.
The steps outlined above can help you manage projects effectively, anticipate risks, and intervene as needed to ensure timely project completion.
How To Use The Critical Path Method (With Example)
Given below is a project activity example to demonstrate how you can use the critical path method with the steps that follow –
Example:
As the project manager for a new initiative, you have mapped out the following task & their dependencies:
- Activity A can start immediately and has a duration of 3 weeks.
- Activity B starts after Activity A is complete and takes 3 weeks to complete.
- Activity C can start after Activity A is complete and requires 6 weeks.
- Activity D starts after B is complete and spans 8 weeks.
- Activity E can only commence once both C and D are complete and has a duration of 4 weeks.
With these dependencies in place, the next step is to determine the project timeline using four key scheduling parameters: Earliest Start (ES), Earliest Finish (EF), Latest Start (LS), and Latest Finish (LF) calculations.
Earliest Start (ES): The earliest time an activity can begin, considering its dependencies.
Earliest Finish (EF): The earliest time required to complete an activity.
Latest Start (LS): The latest time an activity can begin without affecting the overall timeline.
Latest Finish (LF): The latest time required to complete an activity without delaying the project.
(Refer to the table for values)
1. Create a Network Diagram
- Identify all project activities and their dependencies.
- Represent tasks as nodes and dependencies as arrows connecting them.
Task
Estimated Duration
Dependencies ES EF LS LF Float A 3 - 0 3 0 3 0 B 3 A 3 6 3 6 0 C 6 A 3 9 8 14 5 D 8 B 6 14 6 14 0 E 4 C, D 14 18 14 18 0
(CPM Network Diagram template for reference)
2. Perform Forward Pass (Earliest Start & Finish Times)
- Begin at the project start and move towards the end.
- Calculate the Earliest Start (ES) and Earliest Finish (EF) for each activity using:
EF = ES + Activity Duration
For Example:
Calculate EF for A as:
EF(A) = 0+3 = 3 - For activities with multiple predecessors, take the latest EF as the ES of the next task.
3. Perform Backward Pass (Latest Start & Finish Times)
- Start from the project end and move backward.
- Calculate the Latest Finish (LF) and Latest Start (LS) for each activity using the:
LS = LF – Activity Duration
For Example:
Calculate LS for B as:
LS(B) = 6 – 3 = 3
- For activities with multiple successors, take the earliest LS as the LF of the preceding task.
4. Determine Float (Slack) for Each Activity
Float = LS – ES (Start Formula)
Float = LF – EF (Finish Formula)
5. Identify the Critical Path
To identify the critical path, map all project activities, define dependencies, and calculate start and finish times as mentioned above. Focus on tasks with zero float, as any delay in these directly impacts the project timeline.
Note: Activities on the critical path have zero float
(CPM network diagram based on the example)
6. Analyze & Optimize the Schedule
- Allocate resources efficiently by focusing on critical tasks.
- Identify potential delays and adjust dependencies if needed.
- Use float in non-critical activities to manage resource allocation.
The structured approach ensures optimized project timelines, thus identifying bottlenecks before they impact completion.
Conclusion
Projects should follow a timeline to get completed at the rate at which they are started and not left halfway. Tools like the Critical Path Method, as part of the entire project management tools and techniques, are efficient to achieve just that. With the foreseen knowledge of all the tasks and dependencies, and then using the critical path method to estimate the float and the sequence of tasks on the critical path, you can complete the projects on time.
