We know what you’re thinking: Oh no, not another project management acronym.
The US Navy initially developed the program evaluation and review technique, or PERT, in 1957 while secretly creating nuclear submarines.
But you don’t need to be working on top-secret weapons to make good use of the technique. And despite its age, it’s still a popular project management tool today.
PERT is a framework that can help you map out task dependencies and estimate how long your project will last.
In this article, we’ll cover what PERT is, how you can work with it, as well as alternatives that better suit certain use cases.
Use the links below to jump ahead:
- What does PERT mean?
- The building blocks of PERT
- How to use PERT for your project to estimate a timeline
- Why PERT charts aren’t commonly used anymore
- An easier way to visualize and estimate project timelines
What does PERT mean?
PERT stands for Program Evaluation and Review Technique, and it’s a way to estimate the total duration of a project with many moving parts.
A PERT chart helps you visualize a project schedule or timeline as a flowchart. It’s useful during the early stages of planning, when you’re still trying to figure out how all the pieces go together.
For example, a project with 7 key activities and a total project duration of 14 days, could have a chart that looks like this:
Does it feel like you’re staring at a Jackson Pollock painting?
Don’t worry, it’ll make more sense as you read on.
The numbers help you identify the tasks while the lines show you order, duration, and dependencies.
For example, you can’t start activity 6 until both 2 and 4 are completed.
So, the team responsible for that activity doesn’t need to start work until 8 days into the project (2 days for Task 1 plus 6 days for Task 2).
You can also use the PERT framework for projects on a much larger scale.
For a longer and more complex project, you can replace days with weeks or months and adjust how you split activities into larger groups. You may want to focus on deliverables rather than the required tasks so your flowchart doesn’t become a nightmare of lines and bubbles.
We promise this is all going to get clearer as we break it down. Just stay with us for a little longer.
How is it different from CPM?
In project management, CPM, or the critical path method, is a way to calculate the longest “path” or duration until a project is finished. It works by analyzing the longest stretch of dependent activities. You don’t need any visualization to figure it out, although it is helpful, and often used as part of the process.
In fact, project managers often use the PERT chart to show the critical path, which is why the 2 sometimes get confused.
But, the PERT technique was designed as a statistical tool to visualize the overall project schedule, not just the critical path. It shows the relationship between tasks as well as the overall project duration.
In PERT charts, the critical path is often highlighted by position (in the center) or with a different color.
The building blocks of PERT
Understanding the building blocks of PERT will help you not just work with PERT. It will also manage projects better, regardless of method.
A dependency is when one task or project activity can’t happen without a related activity being kicked into motion first. For example, you can’t launch a new Facebook ad campaign without a completed landing page.
It’s tempting to think of dependencies in a strictly linear fashion, like 1, 2, 3. But that’s rarely the case.
Usually, it’s a more complicated relationship. For example, when creating a new website, every other team is waiting on the initial design.
Once the design is ready, developers, copywriters, and the marketing team can start working in tandem.
After developers have created the website, writers finish the copy. Once the ads are ready, they can finalize the site and organize a big launch.
Many projects have more moving parts, and as a result, even messier timelines.
In PERT, activities or tasks are usually called events, and they include the start, duration, and finish of a task.
If you want to get more granular, you can expand on the events with sub-activities. But, keep in mind the more info you have in your PERT chart, the harder it is to read.
Time estimates and calculating the final estimate
You need to identify the predecessors and successors of events based on their dependencies. Then, you can use this information, along with the event durations, to map out your overall timeline.
According to US Census data, the average construction project takes 7.7 months to complete. That’s after construction itself has begun.
If you include design, planning, and post-construction work (like selling apartments), a single project could last for years.It’s essential to be realistic when estimating time frames and scheduling dependent tasks. You wouldn’t want a team to be stuck waiting for several weeks or months, with nothing productive to do.
PERT addresses this issue by using 3 different time estimates for calculating durations.
- Optimistic time: The minimum possible time estimate for an activity or whole project. This assumes everything goes unusually smoothly with no hiccups.
- Pessimistic time: The maximum possible time estimate for an activity or whole project. How long would it take with multiple large issues and bottlenecks?
- Most likely time: The best estimate for an activity or whole project. Think of an average project where a few things go wrong.
In PERT, you use the combination of these 3 times to calculate the PERT estimate. The final estimate is the number that you’ll use in the actual flow chart to find a full project duration.
Formula for calculating the final estimate: (0 + 4M + P) / 6
So, add together the optimistic and pessimistic time, then add in four times the most likely time. To find the final estimate, divide everything by 6.
If 0 is 15, P is 30, and M is 20, the PERT estimate is 20.833. The resulting duration is also called “the most expected estimate.”
You could also use the different time estimates to deliver a range of assessments for project completion, if you really wanted to. But, this gets into monte carlo territory and usually requires advanced simulation software — you don’t want to be doing this type of ‘what if’ analysis with pen and paper.
How to use PERT for your project to estimate a timeline
Okay, so how do you actually use PERT? Let’s walk through it with an example.
First, you need to write down the primary moving parts and how they’ll interact.
It’s easiest to start with a simple 3-column table. (If you want to show the 3 different time estimates in your table rather than calculating them separately, just add in 3 more columns.)
Now, divide the project into different activities or tasks, and note what dependencies they have.
Then, estimate the task duration for each using the PERT range from optimistic to pessimistic. Calculate the most expected time using the formula (0 + 4M + P) / 6.
Finally, fill out the table with the resulting duration for each task.
|Task||Predecessor (Dependencies)||Duration (days)|
|Task E||B, C, D||2|
Once your table looks like this, you’re ready to move onto the next step.
From here, you can draw the flowchart manually, or you can use any diagram or flowchart tool.
The most basic version of the chart includes time as brackets following activity IDs or task names. For a small-scale project, it doesn’t take long to draw or mockup in a program.
This initial network diagram is the most basic implementation of a PERT analysis. You can also use this visualization to find the critical path.
Finding the critical path
When you’ve mapped out the project with PERT, finding the critical path is straightforward. All you need to do is find the longest-lasting string of dependent tasks. One activity can be longer than many others combined, so the number of pieces doesn’t matter.
In the example above, the maximum project length is 19 days. The longest path follows the tasks: A – B – E.
Of course, unless you design the chart deliberately, you won’t automatically find the longest path in the middle. It could hide anywhere in the graph, depending on dependencies and durations.
Why PERT charts aren’t as popular anymore
We won’t lie, we know that was painful. If you’ve made it this far without thinking “I am never going to use this!” then you’re a rare breed.
With the advent of personal computing and modern project management software, PERT charts have started to fall out of favor. Manually creating a mockup doesn’t cut it anymore.
There is a better way.
In many ways, the “spiritual successor” of the PERT chart is the Gantt chart, which automatically visualizes the timeline and dependencies of tasks for you.
What’s the difference between PERT and Gantt charts?
PERT charts are flow chart visualizations of an early-stage project length estimate.
Gantt charts are more granular visual representations, with bar charts arranged linearly for every activity in the project.
You can easily see the total duration for the entire project, from the start date until the last activity is completed.
Creating a Gantt chart is also a lot easier. All you need to do is fill out a table with the dependencies, start dates, and estimated durations.
A Gantt chart doesn’t include an official formula for calculating expected durations. So, if you want to use the PERT method of calculating timelines, you can.
But digitized Gantt charts and project management software isn’t the only reason PERT isn’t as popular.
There are also new methods for working with and visualizing the critical path.
The critical path and activity-on-node diagrams
While initially using PERT to visualize the critical path was quite common, over the last few decades, most companies have transitioned to using new CPM-specific diagrams.
One option is the “Activity-on-node” diagram. It includes metrics specific to the critical path, like drag, total flow, and latest possible start estimates.
We’re not going to go through a step-by-step of how to do this; we’ve made your eyes glaze over enough for one article.
Just know the option is out there, and it provides more info for planning than the traditional PERT method.
Again, to create a network diagram or flowchart like this requires more work than an auto-generated Gantt chart.
An easier way to visualize and estimate project timelines
Thankfully, you no longer have to manually map projects out in a flowchart or network diagram using nothing but a pen, paper, and your intuition.
With monday.com, you can use an easily-customizable template to generate a Gantt chart in minutes. You can also drag-and-drop tasks and edit durations directly on the visual timeline.
Start with the project timeline template
If you want to visualize an upcoming project schedule, start with the project timeline template.
It will create a board with all the variables you need to edit, along with tasks, dependencies, durations, and more.
Add activities, time estimates, and dependencies
Once you’ve created the board, you need to fill it out with the activities that you’ve planned for the project.
At which level you group the project activities or deliverables depends on a few factors. For example, how early in the planning process you are, or the overall scope of your project.
If you’re planning the design and creation of a new product, you could stick to the original template grouping.
If you’re using some A/B tests to determine future changes on your website, you should single out individual deliverables.
Add Gantt view to the table
Once you’ve broken the project down into activities with a given duration, you can add a Gantt or timeline view.
Click the “Main Table” link in the top-left corner of the board. Hover your mouse over the “+ Add View” link and click “Gantt” to add the view.
After you’ve added the view, you can switch between the main table view and Gantt by clicking the same link. It’s that easy.
Edit the settings to get the overview you want
By default, our Gantt and timeline views break down tasks by people, not projects. That’s because as a manager or team leader, you’re responsible for people and their actions, not clear-cut pieces of a physical item.
But for early-stage planning, before even assigning tasks, you can change the grouping if you want to see tasks.
Move to the Gantt view, and click the settings link in the top right corner. Then, set the “Group by” option to “Groups.” That will let you focus on separate tasks or projects, rather than people.
You can also change the color settings to showcase the current status of activity.
Do you want a better grasp on the timeline of a long-term project? PERT will help you get there. But it’s not the most user-friendly method on the market.
Fortunately, visualizing doesn’t have to be a complicated task that makes you want to pull your hair out.
You don’t have to struggle with tables, spreadsheets, or flowchart and diagram software. (We can hear your sigh of relief.)
Our intuitive project timeline template makes adding tasks, durations, and dependencies easy. You can create a visual representation of your project schedule in just a few minutes.