Jory MacKay
Jory is a writer, content strategist and award-winning editor of the Unsplash Book. He contributes to Inc., Fast Company, Quartz, and more.
January 03, 2023 · 10 min read

How to Plan Successful Projects With The Critical Path Method

How to Plan Successful Projects With The Critical Path Method

For most project managers, it’s not the beginning or end of a project that’s difficult to plan for - it’s the “messy middle.” Even with the best scope of work and an actionable project plan, it’s impossible to know what might happen once you start working towards your goals.

The critical path method - commonly known as CPM - is one of the best ways to remove uncertainty and clearly identify and plan out the essential steps of your project.

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It can be a lot of work to plan out your critical path, but the result is often less risk and time wasted on non-value-adding tasks, and ultimately a greater chance of project success.

In this guide, we’ll explain the essential steps of the critical path method, what makes it so effective, and how to use it on your own projects.

What is the critical path method (CPM)?

The Association for Project Management (APM) defines the critical path method as:

“A technique used to predict project duration by analysing which sequence of activities has the least amount of scheduling flexibility.”

But, what does that really mean?

In simple terms, the critical path method is a technique used by project managers to identify and schedule the most time-critical tasks for their projects. This is essential because if any critical tasks are delayed, the whole project will be delayed, too.

For this reason, project managers have used CPM for over 50 years to manage project risk by identifying the tasks that need the most attention and oversight.

It’s not the beginning or end of a project that’s difficult to plan for - it’s the “messy middle.”

Famously, CPM has been used to plan and deliver projects such as the World Trade Center and the Manhattan Project, and has even been featured in fictional books such as Odds On by Michael Crichton.

But CPM isn’t just a fancy planning technique.

The critical path method delivers a whole host of benefits, such as:

The essential elements of the CPM (+ definitions)

Before diving into the somewhat complicated process of critical path analysis, it’s important to first understand the main elements that underpin CPM.

When defining your CPM, you’ll need to understand the following terms:

Creating your WBS, calculating your task durations, and identifying dependencies are key prep work items for your critical path analysis and will be set up like this:

How to prepare the Critical path method boxes

On the other hand, the exact task timings and float are worked out as part of the CPM process.

It’s key to remember that CPM helps you identify your critical tasks, you won’t know which tasks are critical beforehand. That’s because no two projects are the same. The same task can be critical in one project, but not necessarily critical in another. It all depends on the unique scheduling of that project.

To bring CPM to life, let’s move on to look at how you can execute your own critical path analysis.

The Critical Path Method isn’t just a fancy planning technique.

How to identify your project’s critical path (6-step guide)

The good news is that identifying your project’s critical path isn’t rocket science. If you follow these six simple steps, you’ll be able to create your own critical path in a matter of hours.

1. Create your Work Breakdown Structure

To adequately plan the project you first need to understand all the work and tasks required to deliver it. This granularity will help you map out your critical path.

How to do it:

Practical example:

John is Project Manager at Web4U, a Website Development Agency. John is given a new project to build a website for a client. He starts by building a Work Breakdown Structure, breaking down the tasks he’ll need to complete to deliver the project. To make it easier, he divides the work into three phases: Design, Build, and Test & Launch.

Create your Work Breakdown Structure

2. Estimate your task durations

How will you ever know the duration of your project if you don’t know how long each work item takes?

Understanding your task durations (D) will allow you to map your critical path and understand where the pinch points and bottlenecks may be.

How to do it:

At this stage, it’s all about asking the experts and learning from people who have been where you are now. Here are a few different ways you can properly estimate task duration:

Pro tip: Especially in Government projects, there are often great resources online that explain the estimating techniques behind a publicly funded project.

Practical example:

First, John puts each task into a table, giving them a unique ID number. He then estimates how long each task will take to complete in the number of days. John is an experienced web development Project Manager, so he uses data from previous projects to estimate this one.

Estimate your task durations

3. Identify task dependencies

Your most critical tasks will be the tasks that either enable or block progression. So, you need to understand where the dependencies lie. Once you do this, your end-to-end scheduling will come to life.

How to do it:

Practical example:

John sits down with another Project Manager, Sarah, at Web4U and brainstorms the dependencies for his project tasks.

Even though John has completed many projects before, Sarah has more recent experience, so she provides some input. They agree on the project dependencies and map them against the tasks in the critical path planning boxes.

Identify task dependencies

4. Map your tasks (forward pass)

Now that you know the tasks, durations, and dependencies, it’s time to plan them formally. This will give you your project schedule and begin to show how and when you’ll get from start to finish.

How to do it:

Begin with your ‘Forward Pass’, inputting the following for each task:

Complete these boxes for all tasks from start to finish. As you input your data, remember these critical facts:

Practical example:

John begins mapping out his schedule by completing his forward pass. Task A starts on Day 0, with the durations moving forward for each task. At Task E, John takes the highest Earliest Finish (day 15 from Task D) to account for the double dependency.

Map your tasks (forward pass)

5. Review your tasks (backwards pass)

Once the forward pass is complete, you need to head backwards to fully assess the criticality of each task. This is the stage where the critical path really comes to life, and you’ll be able to see the key differences between tasks.

How to do it:

To begin, start with the final task in your schedule. The Earliest Finish (EF) becomes the Latest Finish (EF), as you can’t finish at two different times.

Next, work backward in the opposite way you did for step 4, filling out the following boxes as you go:

Complete these boxes for all tasks from start to finish. As you go through them, remember these critical facts:

Practical example:

John completes the backward pass for his project tasks. For this, he starts by taking the Earliest Finish (EF) from Task F and making it the Latest Finish (EF). From there, he subtracts backward. Where Task E has two pre-requisite tasks, both Task C & D take the same value of 15.

Review your tasks (backwards pass)

6. Calculate float and identify your critical path

With your task, dependencies, and durations mapped out, it’s now time to identify whether each task has a float. Crucially, the tasks with no float have no room for error, and as such, they’re your critical ones.

How to do it:

Practical example:

Now that John has completed his backward pass, he calculates the Float for each task. John realizes only one task, Task C, has any Float, meaning Tasks A, B, D, E, and F make up his critical path. John now knows which tasks are critical, and if any of them are delayed, the entire project will be too.

Calculate float and identify your critical path

Examples of how to use CPM on your projects

CPM is a powerful tool for helping you identify the risky tasks in your project. Here are some other key ways CPM can help you and your project succeed.

The Critical Path Method is one of the best ways to remove uncertainty from your project.

Critical path method (CPM) vs. PERT vs. Gantt charts

Critical Path Method isn’t the only way to estimate projects. PERT and Gantt are two of the other most popular scheduling techniques available to project managers.

Let’s look at how they compare to CPM.


What is PERT?

Program Evaluation Review Technique (PERT) is a planning tool used to calculate the time it will take to complete a project when the task durations are unknown. With PERT, project managers create three different estimates of their project based on:

Then, working backward from a fixed point, PERT is used to determine if a project is achievable and the most likely timeline.

What’s the difference between PERT and CPM?

PERT is often used when project managers don’t know how long tasks will take, or they need to work backward from a fixed delivery deadline.

While PERT charts look similar to CPM, the CPM technique is used to schedule known project tasks and surface any critical dependencies by identifying float.

What is PERT?

Gantt charts vs. CPM

What is a Gantt chart?

The Gantt chart is the most popular planning tool used in project management, showing tasks displayed against time. Typically, tasks are listed on the left, with task bars going left to right to show their sequencing, start and end dates, and duration.

What’s the difference between a Gantt chart and CPM?

Typically, Gantt charts don’t show how different tasks and activities relate to one another, instead, they simply show how they happen over time. This is the key difference to CPM, where a project manager can identify their project’s critical path of interdependent tasks.

Gannt Chart showing progress

Let Planio help you stay focused on your most critical tasks

The Critical Path Method is one of the most commonly used planning tools, helping project managers identify the tasks that really matter. Understand those tasks, and you’ll be able to prioritize better, solve problems faster, and use your resources more efficiently.

And while many think that critical path analysis is hard, if you link it with other project techniques, such as a Work Breakdown Structure, it’s easy to granulate, define, and schedule your project’s work.

Gannt Chart showing finely granulated tasks

And if you need an extra helping hand, tools like Planio are ready to become the center of your project planning universe. With features for creating, linking, and mapping tasks, Planio helps you gain visibility of your work and bring your entire team onto one page.

Try Planio for yourself free for 30 days (no credit card required!)