What is Critical Path Method

Guide: Critical Path Method (CPM)

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Daniel Croft

Daniel Croft is an experienced continuous improvement manager with a Lean Six Sigma Black Belt and a Bachelor's degree in Business Management. With more than ten years of experience applying his skills across various industries, Daniel specializes in optimizing processes and improving efficiency. His approach combines practical experience with a deep understanding of business fundamentals to drive meaningful change.

The Critical Path Method (CPM) is a useful tool in modern project management, used to effectively plan, schedule, and execute complicated projects. Based on the concept of identifying the longest sequence of dependent tasks, CPM focuses on determining and managing the minimum time required for project completion.

This method is based on the concept of the ‘critical path’ a chain of tasks in which timing is important, as any delay to these directly impacts the overall project timeline. Through its structured approach, CPM provides project managers with a framework for managing complex tasks, from constructing a house to orchestrating large-scale industrial projects, ensuring efficiency and timeliness in execution.

Table of Contents

The CPM dates back to the 1950s and originated from a collaboration between chemical giant DuPont and Remington Rand Corporation. It was initially developed to manage large-scale maintenance activities in chemical plants. Over the years since then, CPMs utilisation has expanded its original scope and has been applied in a range of sectors such as aerospace, construction and even recently in software development. 

Key Components of CPM

Before getting into creating a CPM, it is useful to understand the components of a CPM. Most of these will be found as part of a project management Gantt Chart.

Activities and Tasks

In CPM, a project is made up of a range of various tasks or activities that contribute to the overall completion of the project. Such as the house example:

  • Foundation
  • Walls
  • Roof
  • Windows and Doors
  • Plumbing and electric

These activities may be broken down into sub-actions, but they all contribute to the housebuilding process.

Identifying these tasks is the first step of the CPM and is the foundation for further analysis and planning.


The next component is the duration of each task or activity. This duration is an estimate of how long will be required to complete a task. This will help for the planning and understanding of when dependent tasks can start. For example, you are unable to start the activity of putting the roof on the house until the walls are fully built.


CPM then requires an analysis of the dependencies between tasks. These dependencies will dictate the sequence of the tasks. As explained above, some tasks cannot start until others are completed. Therefore, it is important to understand the relationships between vital steps when creating a project schedule.


Finally, milestones are used in CPM to highlight significant points or events within the project’s timeline. Milestones can often represent the completion of key phases or deliverables in projects. In a DMAIC project, a milestone might be the completion of the define phase.

The Critical Path

The identification of the critical path is a combination of analyzing the components of CPM. By identifying the longest sequence of tasks, project managers can identify which activities are important to the timely completion of the project. If any of these critical activities are delayed or extended, this will result in the project duration being extended. Therefore, managing and monitoring these tasks becomes a key focus for project managers to ensure success.

Steps in the Critical Path Method Process

The Critical Path Method is a systematic approach used in project management to plan and execute complex projects efficiently. It involves a series of steps, each crucial for the method’s successful application.

Step 1: Identifying Activities and Dependencies

The first step in creating the critical path method involves creating a comprehensive list of all tasks necessary to complete the project. After listing the tasks, the next impacting consideration is to identify the dependencies of these tasks. Dependencies will determine the sequence in which tasks need to be completed. There are typically three types of dependencies:

  • Finish-to-Start: A task must be finished before the next can start.
  • Start-to-Start: A task must start before or simultaneously with another.
  • Finish-to-Finish: A task must finish simultaneously with another.

Understanding these dependencies is crucial, as it creates the foundation for creating an accurate project schedule.

Step 2: Estimating Duration

Each task identified in the first step should be assigned an estimated duration. These estimations should be based on historical data, statistical methods, or expert judgment. The accuracy of estimating the duration is important, as it significantly affects the reliability of the project schedule. It’s important to consider various factors like resource availability, working hours, and potential bottlenecks while estimating durations.

Step 3: Creating a Network Diagram

With the tasks and their dependencies identified, the next step is to create a network diagram. The network diagram will represent the project’s tasks and the sequence in which they are to be completed, similar to how a process map would show the order of a production process. There are two common types of network diagrams used in CPM: the Arrow Diagramming Method (ADM) and the Precedence Diagramming Method (PDM). These diagrams help in visualizing the flow of the project and are essential for identifying the critical path.

Step 4: Calculating the Critical Path

Following the creation of the network diagrams, the next step is to calculate the critical path, which is the longest path through the network diagram but will also represent the shortest possible duration to complete the project. 

To calculate the critical path you should determine the earliest and latest that each activity can start and finish without delaying a project. Tasks on this path cannot be delayed without affecting the project’s overall timeline. This step is crucial for prioritizing tasks and managing timelines effectively.

Step 5: Allocating Resources

After identifying the critical path, the next step is to allocate resources to the tasks. Resources include people, materials, equipment, and budget. The critical path tasks should be given priority to resources to ensure they have everything needed to avoid potential delays. This step may require some balancing of resources throughout the project to optimize both efficiency and cost.

Step 6: Monitoring

Finally, step 6 is to continue to monitor and adjust the process with resources as the project progresses. Regular reviews will be necessary as the actual duration of activities, resource availability, and other factors may differ. Continuous monitoring allows project managers to identify variances from the plan and make necessary adjustments. Tasks on the critical path are particularly closely monitored, as any delay in these tasks could extend the overall project duration.

Benefits and Limitations of CPM


The Critical Path Method (CPM) improves project management through improved planning, time management, flexibility, and risk mitigation.

Another key advantage of CPM is its focus on time-sensitive tasks. By identifying the critical path, it highlights tasks that directly impact the project’s completion time, helping in prioritize efforts and avoid delays in these crucial areas.

CPM will also highlight tasks not on the critical path, which usually have scheduling flexibility or ‘float’. This knowledge allows project managers to reallocate resources and adjust schedules without affecting the overall project timeline, providing essential adaptability in the face of project changes.

Finally, CPM serves as a valuable risk management tool. Identifying potential bottlenecks and key tasks, it offers foresight into where risks might occur, enabling proactive steps to mitigate them, such as reallocating resources or adjusting task sequences. This anticipatory approach is vital for navigating potential challenges and ensuring project success.


The effectiveness of the Critical Path Method hinges on accurate task duration estimates; errors here can lead to unrealistic schedules, causing delays and resource mismanagement.

Additionally, CPM’s complexity escalates with larger projects, where numerous tasks and dependencies complicate maintaining an accurate, current plan. Furthermore, CPM’s reliance on fixed time estimates for tasks poses inflexibility, particularly in dynamic project environments where conditions and requirements are prone to change, making it less adaptable to uncertainties and variable situations.

Practical Application of CPM

In practice, the application of CPM is often facilitated by project management software. Tools like Microsoft Project, Primavera P6, and others integrate CPM functionalities, allowing for easier management of complex projects.

These software solutions can automatically calculate the critical path, adjust schedules based on task progression, and provide visual representations of the project timeline. They also help in managing the complexities and providing the flexibility needed to adjust to changing project conditions.


The Critical Path Method is a comprehensive approach that enhances project management through meticulous planning, effective time management, adaptable scheduling, and proactive risk mitigation. While it excels in highlighting time-sensitive tasks and providing scheduling flexibility, its effectiveness is contingent upon precise task duration estimates and can become complex in larger projects.

Despite these limitations, CPM’s practical application, often aided by project management software, offers invaluable assistance in managing the intricacies of modern, dynamic projects. By allowing for the calculation of the critical path, resource allocation adjustments, and ongoing project monitoring, CPM remains an indispensable tool in the arsenal of effective project management strategies.


A: The Critical Path Method (CPM) is a project management tool used to plan and control projects. It identifies the most important tasks (the “critical path”) that directly impact the project timeline. By focusing on these tasks, project managers can ensure efficient use of resources and timely project completion.

A: The critical path is the sequence of tasks that must be completed on time for the project to finish on schedule. If any task on the critical path is delayed, the whole project will be delayed.

A: Float or slack time is the amount of time that a task can be delayed without delaying the project. It provides some flexibility in the schedule and helps project managers plan for unexpected delays or problems.

A: The critical path is calculated by adding up the durations of the tasks on each path through the project schedule. The path with the longest total duration is the critical path.

A: CPM offers several benefits in project management, including improved task coordination, better understanding of task dependencies, more effective use of resources, and the ability to identify potential delays in advance.

A: Yes, CPM can be used in any industry that involves complex projects with multiple tasks and dependencies. This includes industries like manufacturing, construction, software development, event planning, and more.

A: Both CPM and PERT are project management tools, but they are used in different scenarios. CPM is typically used for projects with well-defined tasks and time estimates, while PERT is used for projects with uncertain task durations, using probability to estimate task durations.

A: CPM itself doesn’t handle risks and uncertainties, but it can be used in conjunction with other project management tools and techniques that do, such as PERT or risk management methodologies. The float or slack time in CPM also provides some buffer for unexpected delays or problems.


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Daniel Croft

Daniel Croft is a seasoned continuous improvement manager with a Black Belt in Lean Six Sigma. With over 10 years of real-world application experience across diverse sectors, Daniel has a passion for optimizing processes and fostering a culture of efficiency. He's not just a practitioner but also an avid learner, constantly seeking to expand his knowledge. Outside of his professional life, Daniel has a keen Investing, statistics and knowledge-sharing, which led him to create the website learnleansigma.com, a platform dedicated to Lean Six Sigma and process improvement insights.

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