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.
June 20, 2023 · 9 min read

What is a PERT chart? How to use PERT to plan your projects

What is a PERT chart? How to use PERT to plan your projects

Projects fail for many reasons — but one of the most common is poor planning. In fact, studies have shown that around 27% of projects fail because of inaccurate task estimates, with another 11% failing due to undefined task dependencies.

If you want to run successful projects, you need a system in place that helps you avoid these massive issues. That’s where PERT comes in.

Founded by the U.S. navy in the 1950s, the Program Evaluation Review Technique (or PERT) helps project managers worldwide estimate, plan, and visualize their projects in a way that allows them to succeed.

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In this guide, we’ll explain how PERT works, compare it to other more modern project planning methods, and give you a six-step guide on how to create your first PERT chart.

What is PERT in project management? Why would you use it?

The Program Evaluation Review Technique (PERT) is a statistical-based project management technique designed to identify, analyze, and plan the activities that make up a project.

In many instances, the first time you’ll come across PERT is when you see the output of the PERT process — better known as a PERT chart.

Similar to a Gantt chart or a Critical Path map, a PERT chart makes it easy to visualize the total duration of your project by mapping out each task, their minimum durations, and the dependencies between them.

Example of a PERT chart

If you’re new to the world of PERT, that chart might seem overly complicated. But there’s a reason why project managers continue to use PERT charts 70+ years after they were first invented.

Here are a few of the benefits you can expect to see from using PERT to manage your project’s timeline:

A PERT chart might seem complicated, but there’s a reason why project managers continue to use it 70+ years after they were first invented.

Ultimately, a PERT chart can help you get a high-level view of all of the steps required to successfully complete a project. But is it still a viable option for project managers in 2023?

The essential elements of PERT

To see the true benefits of PERT, you first need to understand the elements that go into creating a PERT chart and planning your project.

The PERT process starts with the day-to-day tasks and then builds up step-by-step until you get a complete understanding of your timeline and the tasks that fill it up.

Here’s a breakdown of the essential elements used in PERT:

Activities: What needs to be done

Within PERT, the actual doing of a task is called the “activity”.

The easiest way to remember this is because, like any other activity, that’s when things are actually happening. All activities require resources to complete them, such as human labor, materials, or technology.

Events: When you’ll be doing them

An “event” in PERT refers to a point in time that an activity (or a group of activities) starts or finishes.

Crucially, events don’t take up any time, or use any resources, they’re simply markers within your project plan. If we use the analogy of running a race, you can view events as the start and finish line for each activity.

Dependencies: What needs to come first

Like all project planning techniques, PERT relies on identifying dependencies between different activities.

While you’ll complete your planning by identifying dependencies between activities, in practice, the events rely on each other. For example, you cannot pass the start line for Task B, until you’ve passed the finish line for Task A.

Time: How long everything will take

Lastly, to make a project plan a project plan, you need to estimate the amount of time each activity will take.

This is where PERT is more advanced than other estimating techniques. This is because it uses a formula to average the shortest, the most likely, and the longest estimate of each task to provide a weighted view.

We’ll explore the full formula and how to use it in our guide later on.

Bringing all of these elements together

PERT takes all of these elements and makes sense of them in a way that’s easy to track and share with stakeholders. Here’s what the process looks like at a high level:

PERT chart pros and cons (and when to use one)

Given PERT has been around for a while, it’s proved itself to be an easy-to-use and reliable method of planning projects. But, like all techniques, it’s not without its flaws.

Here are some of the pros and cons of the PERT technique, and when you might decide to use it as a project manager:

Pros and Cons of the PERT chart

Based on these pros and cons, we’d recommend using PERT in the following situations:

6 steps to create a PERT chart (including real-life case study)

Now that you have all the information you need, it’s time to start planning your next project using PERT. To walk you through the process, we’ve put together a 6-step guide to help you create an accurate, easy-to-understand PERT chart that you and your team can use to deliver.

1. Identify and gather all of your project activities

The PERT process begins by identifying all of the tasks, known as ‘activities’ in PERT, for your project. This helps you start the project planning process and uncover your project’s scope of work, resource requirements, and budget.

Planio issue list

Top tips:

Real-life case study:

Jack’s a Project Manager at ZeroLimits, a software development agency specializing in website builds for start-up companies.

Jack’s client, a cyber security recruitment agency, needs an MVP of their website completed within 15 working days. Jack decides to use PERT to plan the project and starts by mapping out the activities.

Here’s what that looks like:

PERT table showing mapped activities

2. Define the project activities’ dependencies

With your activities laid out, the next step is to identify and record any dependencies between the tasks. This is important as it will help you see your critical path and identify any bottlenecks or pinch points.

Top tips:

Real-life case study:

Jack works through his list of activities and maps out the dependencies between the tasks.

He works to reduce the dependencies as much as possible, challenging the team to work on the back end development while the UI/UX design is still underway. He records everything in the table and shares it with the team.

PERT table showing the dependencies of the tasks

3. Connect the dots, highlight the events, and visualize your project’s flow

At this point, you can create the first visualization of your PERT chart by connecting the activities. While tables and lists work well, nothing beats seeing a simple visualization to begin bringing your project to life, especially as you can clearly see your project’s PERT events.

Top tips:

When visualizing any project plan, we’d always recommend doing this within a project management software tool. Tools like Planio help you get stuff done and allow project team members to collaborate, exchange ideas, and store crucial documents all in one place.

Gantt chart planning in Planio

If you’d like to learn more about how we do it at Planio, head over to our task management and planning workflows page here.

Real-life case study:

Jack connects the dots in his PERT activities to map out the beginning of his project plan. He’s relieved that it’s a reasonably linear project with room for flexibility around tasks B-F. Given that task F, “Testing”, relies on both D & E to be completed, he identifies this as a pinch point and logs it on the risk register.

Here’s what Jack’s project would look like on a PERT chart:

PERT chart mapped out

4. Estimate each activity with the PERT formula

Estimating is where PERT separates itself from other planning techniques thanks to its scientific formula approach.

To estimate each activity, you complete a weighted estimate, adding together your most optimistic time estimate (best case), your most likely estimate, and your most pessimistic estimate (worst case).

The estimate is weighted by multiplying your best case by four before dividing the total number by six to provide a final PERT activity estimate:

PERT formula

Repeat this process for each task until you’ve estimated the entire project.

Top tips:

Real-life case study:

With his activities and dependencies mapped out, Jack begins estimating the duration of each task in days. He goes through one-by-one, inputting a best-case, most likely, and worst-case estimate for each activity. Using the weighted estimate formula, he calculates the final PERT estimate for each activity and records them in the table.

PERT table fully filled out

5. Create your end-to-end timeline and align with stakeholders

Now that you have all of the components of your PERT chart, it’s time to put them all together to fully visualize your end-to-end timeline. The benefit of a PERT chart is that it creates an easy document for you to align your stakeholders with and discuss the wider plan for the project.

Top tips:

Real-life case study:

Jack finishes his PERT chart by overlaying his activity estimates and re-formatting for simplicity. He arranges a meeting with his key development team members to align on the plan.

Then, he arranges a meeting to present it to the client, safe in the knowledge the project should take 13 days, well within the 15-day target.

PERT chart end-to-end timeline

6. Review, iterate, and re-align as the project progresses

All projects experience twists and turns, so you shouldn’t just complete your PERT planning once and then leave it be. The best project managers continually review their plans as things change around them. This helps them stay on the front foot, keep their stakeholders happy, and deliver the best results.

Top tips:

Real-life case study:

Jack puts a 15-minute task in his calendar to re-review his PERT chart daily. As activities progress, he updates estimates based on actual figures to assess whether the overall timeline might change. This helps him stay ahead of any hiccups to keep his client happy.

PERT charts vs. Gantt charts vs. the Critical Path Method (CPM)

PERT isn’t the only planning technique out there. Gantt charts and the Critical Path Method are two of the other most popular techniques that project managers worldwide use daily.

Estimating is where PERT separates itself from other planning techniques, thanks to its scientific formula approach.

To finish, we’ve put these three options side by side to help you understand the key differences and decide which one could be right for your next project.

Identifies project tasks
Provides simple task estimates
Provides detailed task estimates
Shows the project’s critical path

Shows project dependencies
Easy to see the project progress
Good for complex projects
Time required to create High Low High

Ultimately, the option you choose will come down to the project’s scope and your team’s comfort level. However, here’s a simple guide you can follow:

Use PERT charts to maximize your project’s success

PERT is an excellent technique for project managers that need to bring structure and accuracy to their project planning. While it’s not a one-size-fits-all, PERT is the technique to use on time-critical projects that require military levels of precision.

If you’re struggling to control your project, we recommend finding a project management tool that empowers you to deliver outstanding results.

Packed full of project planning tools, including Gantt charts, Planio could be your new best friend that’s guaranteed to help bring your team together, streamline your delivery, and maximize your chances of success.

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