Critical Path Method for Project Management

The Critical Path Method (CPM) is a vital project management tool that represents the most extended sequence of tasks that must be accomplished to ensure the completion of the entire project.

You can determine the critical path by measuring the longest sequence of dependent activities from start to end.

It can be visually represented by using a Gantt Chart software that can help build a visual timeline of the project.

In this article, we’ll detail in depth the steps for using critical path method for project management, explain how to calculate the length of your project, explain how keeping an up-to-date project schedule allows you to have flexibility within your critical path, and share our helpful project scheduling template to get you started.

What is the critical path method?

The CPM is a sophisticated project management technique to plan, schedule, and manage complex projects. It involves identifying all the tasks needed to complete a project, determining the sequence in which these tasks must be carried out, and then calculating the most prolonged duration of time it will take to complete the project from start to finish. This most prolonged duration is known as the ‘critical path,’ and it provides a clear timeline for project completion.

In CPM, tasks are categorized as ‘critical’ and ‘non-critical.’ Critical tasks must be completed on time to ensure the project is finished on schedule. Any delay in a crucial task will result in a delay in the project. Non-critical tasks, on the other hand, have some flexibility in their scheduling so they’re less likely to cause a delay in the project completion.

CPM is especially valuable for projects with numerous interdependent activities, as it allows project managers to see where potential bottlenecks may occur and where resources can be allocated most effectively. By identifying the critical path, project managers can prioritize tasks, mitigate risks, and better ensure timely project completion.

Benefits of using critical path method in project management

CPM offers many benefits that can significantly enhance the effectiveness of project management. 

• Provide a clear visualization of the project timeline. By illustrating the sequence and duration of each task, CPM allows project managers to gain a comprehensive understanding of the project’s flow, making it easier to plan and manage resources effectively.
• CPM’s ability to identify critical tasks. This not only helps in prioritizing tasks but also allows for the proactive management of potential delays. By understanding which jobs have the flexibility to be delayed without affecting the overall timeline, project managers can better manage changes or issues that arise during the project life cycle.
• CPM aids in risk identification and mitigation. Highlighting the critical path allows project managers to foresee potential bottlenecks or delays and proactively mitigate these risks. This can lead to a significant reduction in project downtime and associated costs.
• CPM promotes better communication within the project team. With a clear visual representation of the project’s timeline, team members can better understand their roles, responsibilities, and the impact of their tasks on the overall project. This can lead to improved collaboration, efficiency, and overall project success.

In summary, the CPM is an indispensable tool in project management, offering enhanced planning, risk mitigation, resource management, and team collaboration capabilities.

How to find the critical path in a project

Step 1: Identify all tasks required to complete the project

Start by listing all the functions or activities that need to be completed for the project’s successful conclusion, also known as a work breakdown structure. When created thoroughly, the work breakdown structure is a roadmap that guides a team when completing projects — whether simple or complex. Here’s a powerful work breakdown structure example from Wrike.

Step 2: Determine the sequence of tasks

Next, identify the order in which the tasks need to be performed. Some tasks may depend on the completion of others before they can begin, while others may be carried out concurrently. This step is crucial in understanding the dependencies and relationships between tasks.

Step 3: Estimate the duration of each task

Assign a time estimate to each task. This should be the total time required to complete each task from start to finish. Make sure to account for any potential delays or issues that may arise.

Step 4: Draw a network diagram

Using the information from the previous steps, draw a network diagram. This visual representation should depict all the tasks, their sequence, and their dependencies. Each task is represented as a node on the diagram, and the arrows between nodes represent the dependencies between tasks.

Step 5: Identify the critical path

The critical path is the longest path from the start to the end of the project, passing through all the essential tasks to the project’s completion. In other words, the sequence of tasks determines the minimum time needed to complete the project. On your network diagram, the critical path is the longest from the initial to the final task.

Step 6: Calculate the float

The float or slack is how long you can delay a task without waiting for the project. Tasks on the critical path will have zero float, meaning they can only be postponed without impacting the project timeline. However, non-crucial tasks may have some float, allowing for some flexibility in scheduling.

Step 7: Monitor the critical path

Once the project is underway, closely monitoring the tasks on the critical path is essential. Any delays in these tasks will directly impact the project timeline. Regularly updating and reviewing the critical way can help identify potential issues early and keep the project on track.

Consider using Wrike’s critical path method template to augment this process further. This pre-structured template simplifies identifying your project’s critical path, saving time and enhancing project planning efficiency. 

Try our template

Critical path method example

Now we’ll try to demonstrate the concept of the critical path method with a simple, real-life example: planning a killer party. How should you plan and execute this project?

1. Define the project scope

First, we need to define all of the tasks that must be finished to complete the project. For our party example, it might look like this:

• Choose a date and venue
• Make the ultimate playlist
• Set up the sound system
• Invite your friends
• Buy the food and drinks
• Cook your famous casserole
• Host the party

When we look at these tasks individually, we realize that some of them cannot be started before the others are completed. That is, some tasks are dependent on others. We’ve designated these relationships in the table below:

The actions “invite your friends,” “buy the food and drinks,” “cook your casserole,” and “host the party” form a sequence of tasks that must be performed in a specific order, one right after the other, to ensure a successful result. Such tasks are called sequential activities.

Together with the start of our project (“choose a date and venue”), these tasks are the most critical steps in completing our project. Thus, these actions will be placed on the critical path.

2. Define different project paths

You can have more than one critical path in a project so that several paths run concurrently. This can result from multiple dependencies between tasks or separate sequences that run for the same duration.

In planning a party, various project paths will consist of tasks that need to be completed. For example, one path could involve tasks related to booking the venue, such as researching options, visiting potential locations, and finalizing the booking. Another path might focus on the catering, which includes deciding the menu, finding a caterer, and arranging the food and drink delivery. Another path could be about entertainment, involving tasks like hiring a DJ or band and planning games or activities.

While separate, each of these paths is an integral part of the overall project and must be coordinated effectively to ensure a successful party. By clearly defining these different project paths, you can better manage the tasks and timelines associated with each one.

3. Consider the resource constraints

Traditional critical path schedules in project management are based only on causal dependencies. We’ve already marked these dependencies in our plan. (e.g., it’s impossible to cook the casserole without buying the ingredients). However, a project may have limited resources that need to be taken into consideration, such as how to calculate load in resource planning. These limitations will create more dependencies, often referred to as resource constraints.

If you work on a team, you may split the project work between team members. In our example, while you’re choosing a date and venue and inviting people, one of your friends can make a playlist, and another can get the food and drinks. The tasks can be done in parallel, as in our chart above.

However, if you’re the only person responsible for the project, you have a resource constraint because you can’t be in two places at the same time. In this case, your critical path will look different.

On the chart above, we assume you first need to choose the date and venue, and only later can you make a playlist. However, depending on the project conditions, these tasks can be performed in a different order.

4. Calculate the length of your project

Let’s assume you have to do everything by yourself. We estimated the length of time each activity will take. Also, we determined the approximate start time for each task on the critical path. Here’s what we came up with:

Now, if we add up all of our critical tasks’ duration, we’ll get the approximate time we need to complete the whole project. In our case, three days and six hours, since “make the ultimate playlist” and “set up the sound system” are not on the critical path. If we add the duration to the start time, we can calculate the earliest project completion time. Understanding the CPM allows us to make this calculation quickly and accurately.

5. Leave space for flexibility

The critical path method was developed for complex but fairly predictable projects. However, in real life, we rarely get to manage such projects. Let’s say you plan to redecorate your living room with a friend.

Your task list may look like this:

1. Get rid of the old furniture
2. Paint the walls
3. Fix the ceiling
4. Install the new furniture

Your friend’s responsibilities are to:

1. Choose the new curtains
2. Hang the new curtains

The curtain tasks form a sub-project and can be treated as a non-critical path. Your friend can “choose the new curtains” and “hang the new curtains” any time before the end of your project. The curtain tasks have flexibility in the start and end date, considered float. These tasks are parallel and will not be placed on the critical path. Here’s how this project would look on a Gantt chart:

If any of the parallel tasks were to be significantly delayed, it would prevent our whole project from being completed on time. Therefore, you should always keep an eye on similar tasks.

6. Adjust to the changes in the critical path

Let’s assume that choosing the curtains took our friend longer than we initially expected. This will delay the end of the project.

Our redecoration is incomplete without the new curtains, so the path that previously was non-critical becomes critical. The initial critical path changes.

To monitor your non-critical tasks, your project schedule must be current. That’s the only way you’ll know exactly where your project is at any given moment and whether it will be delivered as initially planned.

Critical path method vs. PERT

In project management, the CPM and the Program Evaluation and Review Technique (PERT) are valuable tools. However, they each have distinct characteristics and are better suited to different types of projects.

CPM is a deterministic approach that assumes a fixed time frame for each task. This makes it ideal for projects with well-known task durations and little variability, like construction or manufacturing projects. CPM focuses on the critical path, the sequence of tasks that determines the project’s shortest duration. By identifying this path, CPM allows project managers to prioritize tasks directly impacting the project’s timeline.

PERT is similar to the critical path in that they are both used to visualize the timeline and the work that must be done for a project. However, with PERT, you create three different time estimates for the project:

• The shortest possible amount of time each task will take
• The most probable amount of time
• The most extended amount of time tasks might take if things don't go as planned

This makes PERT ideal for research and development projects or any other project with uncertain task durations. While both methods help in project planning and scheduling, PERT’s ability to handle uncertainty makes it more flexible in the face of potential changes or delays. CPM’s focus on the critical path can make managing and controlling tasks critical to the project’s timeline easier.

The choice between CPM and PERT should be based on the nature of your project and the level of certainty or uncertainty in task durations. Both methods offer valuable insights that can help drive project success.

CPM success story

The Hoover Dam, constructed between 1931 and 1936, is a testament to effective project management’s power. While the critical path method hadn’t been formally defined yet, its principles were applied during the dam’s construction. 

The project had many activities, each with dependencies and timelines. The project managers had to coordinate these activities in such a way as to ensure the project was completed on time and within budget. They effectively identified the project’s critical path, focusing resources and attention on the tasks that would cause the most significant delays if not completed on time.

The Hoover Dam was completed two years ahead of schedule despite the project’s complexity. This early completion was primarily due to the effective use of what we now know as the critical path method, making it a compelling case study for successfully implementing this technique. 

This case study provides a practical example of the critical path method in action and illustrates its potential in managing large-scale, complex projects.

How Wrike can help you with your critical path management

Determining the critical path of a project isn’t exactly a quick process. That’s why we’ve designed a pre-built template for project scheduling that will help you progress through the steps of creating your critical path. Our project scheduling template allows our customers to visualize the critical path on a Gantt chart, assign tasks to team members, and drag and drop activities to ensure proper resource management. 

Ready to use Wrike for your critical path analysis?

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Further reading:

Here are some further resources you can use to brush up on your critical path method knowledge:

• The Critical Path Method, Seminar, Stanford
• Explaining the Critical Path Method, U.S. Department of Health and Human Services
• The ABCs of the Critical Path Method by Harvard Business Review
• How to Use a Single Gantt Chart for Multiple Projects
• When to Use a Project Calendar vs. a Gantt Chart