The critical path method in project management: Your guide

The critical path method (CPM) is a sophisticated project management technique for planning, scheduling, and managing the tasks necessary to complete a project from start to finish. It is also sometimes referred to as critical path analysis (CPA). 

The critical path method does two main things:

1. It helps project managers find the most important tasks in a project that critically affect how long a project will take. 
2. It helps project managers make an efficient schedule so they can finish the entire project on time and within budget.

Any team in any industry can use critical path methodology to manage complex projects. What’s more, a good project management software platform will be able to take the CPM data of a project and turn it into a visual representation, displaying the tasks, their dependencies, and the critical path to make it easy to understand and manage the project at a glance. 

In this article, we’ll tell you everything you need to know about the critical path method, and answer questions such as:

• What is the critical path in project management?
• What are the steps for using CPM for project management?
• How do you calculate the length of your project?
• How do you maintain a project schedule that provides flexibility within your critical path?

We’ll also show how Wrike’s project scheduling template and Gantt chart software will help you visualize and manage your project’s critical path. 



What is the critical path method?

The critical path definition

The critical path method involves identifying all the tasks that are 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. 

The most prolonged project duration is known as the critical path, and it provides a clear timeline for project completion.

In the 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 critical 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.

The 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 a project progresses and is completed on time.

Benefits of using the critical path method in project management

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

• CPM provides a clear visualization of the project timeline. It usually looks like a flowchart. By illustrating the sequence and duration of each task, the CPM allows project managers to gain a comprehensive understanding of the project’s flow, making it easier to plan and manage resources effectively.

• CPM clearly identifies 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, CPM is an indispensable tool in project management. It gives you enhanced planning, risk mitigation, resource management, and team collaboration capabilities.

How to calculate the critical path of 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 by incorporating buffers or contingency time into your estimates.

Two techniques that can help project managers accurately determine each task’s duration are the forward and backward pass techniques: 

• Forward pass: Starting from the beginning of the project and moving forward through the critical path diagram, calculate the earliest start time and finish time for each activity. This helps determine the earliest possible project completion date for the entire project.
• Backward pass: Work your way backward from the project’s end date through the CPM chart, calculating the latest start time and finish time for each activity. This helps identify the latest possible project completion date for the project and determines the amount of scheduling flexibility or slack time available for each activity.

Step 4: Draw a network diagram of the critical path

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 task dependencies.

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 longest sequence of tasks determines the minimum time needed to complete the project. On your network diagram, this is your critical path, the longest duration from the initial to the final task.

Step 6: Calculate the float

The total float or slack is how long you can delay a task without postponing the project’s completion. Tasks on the critical path will have zero float, meaning they can’t be delayed without impacting the project timeline. However, non-crucial tasks may have some float, allowing for some flexibility in scheduling.

Within the overall float calculation is also free float, which is the amount of time an activity can be delayed without delaying the start of its successor activity. 

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 update and review the critical path to help identify potential issues early and keep the project on track.

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

Example of the critical path method in action

Now we’ll demonstrate with a simple, real-life critical path method schedule and example: planning a killer party. How should someone 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 famous 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 multiple critical paths 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.

In the table 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 activity duration of each task. 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 in the late 1950s 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 subproject 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 date 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 parallel tasks.

6. Adjust to 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.

7. Compress the schedule (if necessary)

If a project deadline is moved up, you might have to find a way to expedite tasks. While this is not an optimal scenario, there are two ways to accomplish schedule compression within the CPM framework:

• Fast-tracking: This involves overlapping parallel tasks originally planned to be done sequentially in order to shorten the project duration. Fast-tracking can potentially increase project risk due to dependencies between tasks.
• Crashing: This involves the allocation of additional resources (such as manpower or equipment) to critical activities in order to accelerate their completion. Crashing often results in increased costs, so it’s important to let stakeholders know of any budget changes.

Critical path method vs. PERT

CPM and the program evaluation and review technique (PERT) are valuable project management 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. The CPM focuses on the critical path, meaning the sequence of activities or tasks that determines the project’s shortest possible duration. Identifying this path allows project managers to prioritize tasks directly impacting the project’s critical path timeline.

PERT is similar to the CPM 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. The 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 stories

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

The Hoover Dam

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, the principles of its essential algorithm were applied during the dam’s construction. 

The project had many activities, each with dependent tasks 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. 

How Wrike can help you implement the critical path method 

Manually determining the critical path of a project isn’t exactly a quick process. That’s why Wrike has a feature that automatically determines your critical path for you. To use this feature, all you have to do is input these essential elements in your schedule on Wrike:

• Start and end dates of all project tasks
• Duration of each task
• Task relationships or dependencies 

To further facilitate the process, we’ve also designed a prebuilt template for project scheduling that will help you progress through the steps of building out 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 project activities to ensure proper resource management.

If an issue comes up, you’ll have a clear view of how to alter your project schedule without causing delays and missing deadlines. 

Ready to use Wrike for your critical path analysis? Start a free trial now.

Further reading on the critical path method

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

• Critical Path Method, U.S. Department of Health and Human Services
• The ABCs of the Critical Path Method, Harvard Business Review
• How To Use a Critical Path Analysis
• When To Use a Project Calendar vs. a Gantt Chart