PERT chart: all you need to know

The PERT chart, or “ Program Evaluation and Review Technique ” is a project management tool. It allows you to visualize a project divided into sequences of several tasks. Mastering it facilitates teamwork and increases the productivity of a company. We tell you, below, everything you need to know about this tool.

What is the PERT chart?

The PERT chart is a management tool, which was designed by a private American firm in the year 1958. The US Army was the first user. In the midst of the Cold War, it used it to optimize the production of its missiles. It is estimated that during this period, she would have gained up to three years of productivity with these diagrams.

Summarized in a nutshell, the PERT chart is a graphical project management method, which can be drawn on a computer or with a pen on paper. It is used to represent the successions of tasks leading to the execution of a project.

Far from being reserved for the US military, PERT charts are now used by many private companiesacting in sectors as varied as IT, marketing or the automotive industry.

Planning software usually offers PERT chart generation.

PERT chart
PERT chart

Why use a PERT chart

A PERT chart has mainly three advantages. It serves to easily visualizethanks to a graphical representation, all the tasks that have already been completed, are in progress, and still need to be started. This makes it possible to estimate at a glance the degree of progress of a project.

Also, the PERT chart helps to visualize the dependencies between the different stages of the project. This allows you to see at a glance how it fits together. Finally, it should be added that the PERT chart represents the time required to complete each sequence of tasks. These last two functions are very practical to know on which sequence to spend its resources in priority to meet the deadlines.

PERT chart and Gantt chart: the difference

The PERT chart is often reconciled and compared to the Gantt chart. Yet, although they are both used in similar contexts, and for the purpose of productivity, they do not have exactly the same utility. Three differences are worth noting…

Freeform vs orthogonal landmark

The Gantt chart uses a stick representation on an orthogonal mark. On the abscissa is the timeline. Conversely, the PERT chart is free-form : time is only a data displayed in each node.

The advantage of the Gantt chart display is that it allows you to see, according to the length of a stick, the duration of the task to be performed. The Gantt chart is therefore more visual.

Also, on a Gantt chart, time can be expressed in calendar dates. You can thus see at a glance which day of the month corresponds to a deadline. On the contrary, in a PERT chart, dates are expressed relative to a point 0.

Viewing dependencies

Sometimes we attribute the PERT diagram the advantage of materializing dependencies between tasks. It is true that it had this advantage for a time, but the modern form of Gantt charts also makes it possible to materialize dependencies. It is therefore today a tie on this point.

Consideration of margins

The real advantage of the PERT chart over the Gantt chart is its consideration of margins.

Indeed, we display, for each task, the date of completion at the earliest and the date of completion at the latest. The difference between the two values ​​constitutes a margin. This allows you to see on which task it is acceptable to be a little late. This is very useful for optimizing resource management.

PERT Chart: The Benefits

Compared to others project management toolssuch as Gantt charts, or even Kanban lists and boards, the PERT chart has special strengths. Above, we evoked the concept of margin, which makes it possible to optimize the management of the resources and to support the good respect of the deadlines.

It also allows, in a more general way, to represent very visually the dependencies in chains, called sequences, and thus to make sure to carry out the tasks in the good order.



The node of a PERT chart is a circle divided into three compartments. It materializes a stage of the project. In the top compartment is the step number. In the two compartments below are listed the date of completion at the earliest, and the date of completion at the latest. Its stages are the project tasks, as well as the start and end of the project.


On a PERT chart, the dependencies are materialized by arrows, which link tasks together. A task is said to be dependent when the starting point for its achievement is conditioned by the accomplishment of a previous task, called “antecedent”. “.

A succession of dependencies are found in most PERT charts and form paths called “sequences”.

By convention, we annotate next to each of the arrows materializing the dependencies the estimated time of completion of the following task.

Critical sequence

Once the construction steps of the PERT diagram have been completed, the critical sequence is directly apparent. It represents the succession of tasks for which the earliest completion date is the same as the latest completion date.

The critical sequence is, in fact, the one that will take the longest to complete.

It is on the critical sequence that it is necessary to put the maximum of resources so as not to fall behind.


To make a PERT chart, you must first build a table with three columns. These columns correspond to thetask identificationestimated task completion time, and history.

Once this table is built, we can start building the PERT chart. They will show the dates of completion at the latest as well as the critical sequence.

Identification of tasks

Task identification is an arbitrary process. The identity of a task is simply the reference by which your team will recognize it during the project. You can designate a task by a name summarizing it, by a number, or even a letter.

Calculate the duration of each task

There estimated duration of a task is also data whose source is external to the PERT chart. It’s up to you to use the knowledge of your company, your processes, the statistics that you have already collected to try to set the most accurate estimate possible.

Identify dependencies between tasks

In the table serving as the basis for the PERT diagram, we identify the dependencies thanks to the “antecedents” column. If, for example, a task B has a task A as its antecedent, then task B is said to be dependent on task A.

A task can have more than one antecedent. In this case, its achievement is conditional on the accomplishment of as many tasks. On the diagram, we will connect these antecedents of the same level by dotted lines to represent their links. We will then derive the dependency arrow from the antecedent having the longest date of completion at the latest.

Also, some tasks have no antecedents. These tasks are independent. THE independent tasks are started at the beginning of the project, and therefore represented at the left end of the PERT chart. The PERT chart starts with as many sequences as there are independent tasks.

Indicate the date at the earliest and the date at the latest

For determine the earliest completion dates, it is very simple. The earliest completion date of the first task in a sequence corresponds exactly to its estimated completion time. The earliest completion date of the task which is directly dependent on it corresponds to the sum of the estimated durations of completion of these two tasks, and so on.

For determine the dates of completion at the latest, it is necessary to identify the branches where a task is dependent on several others. As we said, the antecedents of the same level are connected by dotted lines. All these antecedents will have a latest completion date equal to the earliest completion date of the critical sequence, ie of the one whose earliest completion date is the highest.


What is the main purpose of a PERT chart?

The main purpose of a PERT chart in project management is to represent the dependencies between the stages of a project. This makes it possible to work in the correct order, and also to see the different sequences of tasks leading to the execution of a project, called sequences. The estimated duration of completion of each sequence being displayed, it is easy to see on a PERT diagram the so-called “critical” moments at which there is a risk of running out of time. This helps to have better resource management to better meet deadlines.

What is the principle of the PERT method?

The PERT methodology revolves around the concept of “network”. The PERT network is the graphical representation of the tasks of a project and their dependencies, with circles called “nodes” that are connected by arrows.

How to make PERT chart in Excel?

To make a PERT chart in Excel, you can simply use the “Illustrations” function, which you will find in the “Insert” tab of the spreadsheet taskbar. Use this function to draw circles and arrows corresponding to diagram nodes and their dependencies.

For automate the creation of a diagram on computers, you can use PERT chart software, free or paid, as you can find quite simply on the Internet.