The critical path method in project management: Your complete CPM guide

The critical path is the longest sequence of dependent tasks in a project. It sets the minimum possible duration, and any delay to a task on the critical path delays the end date by the same amount. 

That’s what separates a critical task from a non-critical one: critical tasks sit on this path and have zero float, meaning they can’t slip, while non-critical tasks have positive float and some room to move. Knowing which is which answers three questions:

• Which tasks can and can’t slip?
• Where can your team reallocate resources?
• How long will the project take at a minimum?

This guide covers how the critical path method works, the formulas behind the forward and backward pass, when to use it over a Gantt chart or PERT chart, and how Wrike automates the calculations for you.

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 run at the same time. 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 can help project managers turn those estimates into an actual schedule: the forward pass and the backward pass.

The forward pass calculates the earliest each task can start (early start, or ES) and finish (early finish, or EF), working left to right through the network:

EF = ES + duration

The earliest start time of a task equals the earliest finish of its latest-finishing predecessor. For the very first task in the project, ES = 0. When a task has multiple predecessors, take the largest EF among them as its ES, since a task can’t start until every predecessor feeding into it is completed.

The backward pass works right-to-left from the project end date, finding the latest each task can start (late start, or LS) and finish (late finish, or LF) without delaying the project.

LS = LF − duration

The latest finish of the final task equals the project duration, which is the EF you calculated in the forward pass. When a task has multiple successors, take the smallest LS among them as its LF, since the task has to finish in time for the earliest of those successors to start on schedule.

Together, the forward and backward passes give you every task’s ES, EF, LS, and LF, which is what you need to calculate float in Step 6.

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. 

You can see the critical path displayed on this diagram:

Here are the task dependencies based on the example above:

• Tasks A and B can run in parallel
• Task D is dependent on A
• Task C is dependent on B 
• Tasks C and D can run in parallel
• Task E is dependent on D
• Task F is dependent on E

The critical path in the example above is 10 days because tasks A–F will take 10 days to complete. If two paths tie on duration, both are critical paths, and must be monitored with equal attention. 

Step 6: Calculate the float

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

You calculate total float from the ES, EF, LS, and LF you found in Step 3:

Total float = LF − EF (or equivalently, LS − ES)

This calculation asks a simple question: how much later could this task finish than its scheduled finish time before it delays the project? 

Say a task has an earliest finish (EF) of day 5, but the backward pass shows its latest finish (LF) can be as late as day 8. That’s 8 − 5 = 3 days of total float. The task could run three days behind its earliest possible finish, and the project would still land on time.

Free float is a narrower version of the same idea. Instead of asking how much delay the whole project can absorb, it asks how much delay the very next task can absorb before its own start gets pushed back.

Free float = ES (next task) − EF (current task)

Take that same task finishing on day 5. If the next task in the sequence has an earliest start (ES) of day 6, the free float is 6 − 5 = 1 day. You could delay the first task by one day without affecting when the next task starts, even though the total float showed three days available before the whole project felt it.

That gap between the two numbers is important. A task can have three days of total float but only one day of free float, because delaying it further would still be fine for the project’s overall deadline, but it would start bumping into the next task’s schedule. Zero float on either measure means no room to move.

A quick way to read the result once you’ve calculated it:

• Zero float means the task is on the critical path and can’t slip.
• Positive float means the task has room to move without affecting things downstream (free float) or the whole project (total float).
• Negative float means the task is already behind schedule, and something needs to change now.

Step 7: Monitor the critical path

Once the project is underway, closely monitoring the critical path tasks 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 further augment this process. This prestructured template simplifies identifying your project’s critical path, saving time and enhancing your project planning efficiency.

Examples of the critical path method in action

Now we’ll demonstrate with a simple, real-life critical path method schedule and example: planning a party. How should someone plan and execute this project?

1. Define the project scope

First, define all the tasks that must be finished to complete the project. For example, if you were throwing a party, your task list 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 you look at these tasks individually, you realize that some cannot be started until others are completed. 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 to ensure a successful result. Such tasks are called sequential activities.

Together with the start of the project (“Choose a date and venue”), these tasks are the most critical steps in completing the project, so they are included on the critical path. 

2. Define different project paths

You can have multiple critical paths in a project and several paths running concurrently. This can result from multiple task dependencies or separate sequences that run for the same duration.

Various project paths surface that need to be completed when planning a party. 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 catering, which includes deciding the menu, finding a caterer, and arranging delivery. Another path could target entertainment, including tasks such as 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.

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 considered, such as calculating load in resource planning. These limitations will create more dependencies, often referred to as resource constraints.

If you work on a team, you can 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 in parallel. However, if you’re the only person responsible for the project, you face a resource constraint because you can’t be in two places at once. 

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 you add up the duration of all the critical tasks to find the project duration, you’ll get the approximate time you need to complete the whole project – in this case, three days and six hours, since “Make the ultimate playlist” and “Set up the sound system” are not on the critical path. 

5. Leave space for flexibility

The critical path method was developed in the late 1950s for complex but fairly predictable projects. However, we rarely manage such projects in real life. 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 current 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” at any time before the end of your project. The curtains task, which has flexible start and end dates, is 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 significantly delayed, it would prevent our entire 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 initially expected. This will delay the project’s completion.

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

To monitor your non-critical tasks, your project schedule must be up to date. 

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 need 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 to shorten the project duration. Fast-tracking can potentially increase project risk due to dependencies between tasks.
• Crashing: This involves allocating additional resources (such as people or equipment) to critical activities to accelerate their completion. Crashes often lead to increased costs, so it’s important to inform stakeholders of any budget changes.

The party planning example works well for walking through the mechanics of CPM step by step. But the method looks a little different when applied to the kinds of projects most teams are actually running. Here’s how the critical path shows up in three common professional contexts.

Critical path method in construction

On a construction project, the critical path typically runs straight through the structural sequence: excavation, foundation, framing, and roof. Each of those tasks depends on the one before it, and none of them can be compressed much without added cost or risk. A delayed concrete pour pushes every subsequent structural task back by the same number of days, and the project’s finish date moves with it.

Interior finishing work often sits off the critical path instead. Tasks like painting, flooring, and fixture installation still need to happen, but they typically have float, since they can be resequenced or run in parallel without affecting the handover date. A delayed tile delivery is a good example. It’s a real problem for the finishing crew’s schedule, but it usually doesn’t affect the project’s overall deadline as much as a delayed pour. 

Critical path method in IT/software

A system migration or software rollout usually has three tracks running at once: development, infrastructure setup, and user training. Each track has its own internal sequence, but they don’t all carry the same weight when it comes to the project’s finish date.

The critical path usually runs through whichever track takes the longest, which is often data migration or the core build. Training tends to have float, since it can’t meaningfully start until the system is ready, but the training team can usually compress or shift their own schedule within that window without delaying go-live. If infrastructure setup or data migration slips, though, the whole project slips with it, since nothing downstream can start until that track finishes.

Critical path method in marketing campaign management

A campaign launch typically runs creative production, media buying, and legal review in parallel. Creative and media buying tend to get the most planning attention, since they’re the visible, deadline-driven parts of the work.

Legal review is the one that quietly becomes the critical path bottleneck. It’s often estimated optimistically or scheduled as an afterthought, only to become the task that determines when the campaign can actually go live. Building legal review into the critical path from the start, rather than rushing it in at the end, gives the team an honest view of whether the launch date is realistic.

Critical path vs. PERT vs. Gantt charts

CPM, the program evaluation and review technique (PERT), and Gantt charts are valuable project management tools. However, each has distinct characteristics and is 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.

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 CPM in that both are used to visualize the project timeline and the work to be done. 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 longest 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 it easier to manage and control tasks critical to the project’s timeline.

Gantt charts, on the other hand, are primarily visual tools used for illustrating the project schedule. Rather than analyzing time variability or task dependencies in depth, as in PERT or CPM, Gantt charts provide a clear timeline that maps tasks along a horizontal time axis. 

They make it easy to track progress, understand overlaps, and see who is responsible for what, especially in team settings. When paired with CPM, a Gantt chart tool can help visualize the critical path and make complex schedules more accessible to stakeholders.

The choice between CPM, PERT, or Gantt charts should be based on the nature of your project and the level of certainty or uncertainty in task durations.

Tools and templates

You don’t need to build a critical path diagram from scratch to benefit from CPM. Today’s project management platforms offer built-in tools and templates that make it easy to map dependencies, identify the critical path, and adjust timelines as work evolves.

Look for tools that offer:

• Visual timeline views (like Gantt charts)
• Dependency mapping
• Task duration tracking
• Automated critical path calculation
• Real-time updates across teams

Modern platforms are also incorporating artificial intelligence to streamline CPM-based planning. For example, some AI project management tools can analyze task data to suggest dependencies, flag bottlenecks, or recommend timeline adjustments based on workload and progress.

If you’re exploring options, here are a few types of solutions to consider:

• Wrike: Our platform offers an advanced Gantt chart tool, dynamic timelines, and built-in critical path visualization. With features like task dependencies, real-time updates, and AI-powered Work Intelligence®, Wrike makes it easy to manage complex workflows with clarity and precision.
• Microsoft Project: A longtime staple in enterprise project management, it provides robust scheduling tools and detailed critical path analysis.
• Smartsheet: Smartsheet combines spreadsheet-style project tracking with Gantt views and dependency management suitable for CPM planning.
• AI-enhanced planning tools: Emerging platforms now include AI agents with capabilities that support smart scheduling, risk prediction, and task reallocation.
• CPM templates: You can also find downloadable or built-in CPM templates that help teams get started quickly, especially for recurring project types like product launches or cross-functional implementations.

Using the right tools not only makes CPM easier to implement but also helps teams stay aligned, adapt faster, and deliver with greater confidence.

CPM success stories

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

The Hoover Dam

The Hoover Dam, constructed between 1931 and 1936, is a testament to the power of effective project management. While James E. Kelley and Morgan R. Walker hadn’t formally defined the critical path method at the time the dam was built, the principles of its essential algorithm were applied during construction. 

The project had many activities, each with dependent tasks and timelines. The project managers had to coordinate these activities 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 a project’s critical path isn’t exactly a quick process. That’s why Wrike has a feature that automatically determines your critical path. To use this feature, all you have to do is input these essential elements in your project 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 to help you progress through the steps of building your critical path. 

Our project scheduling template helps you quickly visualize the critical path on a Gantt chart, assign tasks to team members, and drag and drop activities to ensure proper resource management throughout your project. 

Find out more about how Wrike can help your team find the critical path to a successful project. Book a demo today, or try Wrike free.