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What is PERT?

For project managers who want to get their teams working more efficiently, the PERT program can really help.


History of the Program Evaluation and Review Technique

The PERT acronym stands for “Program Evaluation and Review Technique,” a program that has been in use by various organizations for over 50 years. Originally developed in 1958 for use by the U.S. Navy Special Projects Office, the PERT technique is a project management system designed to assist in planning large and complex projects. Starting with an overall program evaluation, it promotes in-depth analysis of any project before the kick-off date. It was used on the Polaris missile design as well as the 1968 Winter Olympic games held in Grenoble. While similar management concepts have been developed and refined since, PERT was the first technique of its kind.

How PERT project management works

As mentioned above, PERT is designed to be implemented with projects that are highly complex, needing to be completed through sequential tasks and/or run in tandem with other projects. The overall goal of PERT is to get projects completed on time and on budget, as well as to accurately assess their overall scope during the scoping phase.

Scoping your PERT project

Scoping is a crucial part of PERT, as it’s where you create an action plan for your project. The technique makes allowances for things that could go wrong or taking longer than they should, as well as key ”milestones” throughout its life. Compared to your team’s regular scoping technique, PERT might seem extremely in-depth, calling on everything from resource management to individual performance. With its military roots, the PERT method is all about preparation, leaving no stone unturned.

PERT terms for scoping

A PERT scope will use the following terms to define key events, timings and resources:


PERT events serve as milestones in your process. They don’t require any resources in of themselves: instead a PERT event cannot be completed until every task leading up to it is complete.

  • A PERT event refers to the start or completion of one or several activities
  • A predecessor event comes immediately before another event or events
  • A successor event occurs immediately after another event or events


PERT activities are the tasks which require resources:

  • A PERT activity refers to carrying out a task that uses up your resources whether that’s time, materials, money, or even machinery. You cannot perform a PERT activity until the event marking its commencement is completed, e.g. if anything in the previous event phase is unfinished, the new one cannot begin.
  • A PERT sub-activity refers to the smaller tasks a PERT activity can be broken down into. For example, the activity “prepare blueprints” can be broken down to “prepare blueprints 1, 2 and 3” if it’s likely to need multiple sessions.


PERT times are key to the technique and are designed to allow for optimized performance as well as setbacks:

  • Optimistic time refers to the minimum time needed to complete an activity, assuming everything runs smoothly and goes even better than expected
  • Pessimistic time is the opposite, and sets the maximum amount of time needed to complete task, assuming everything that can go wrong, does go wrong—not counting total disasters
  • Most likely time is the happy middle ground when it comes to the predicted time needed, assuming everything runs as usual
  • Expected time is your best guess for delivery, with some allowances for things going wrong, and should be based on the model average time for a routine task completion


Several other terms help define the importance, progress and time expectation of each event or activity:

  • Critical path gives an overview of the whole project from day one to the completion date, and helps define the total time in days, months or years that your team will need to complete everything. The Critical Path Method was actually a separate approach developed around the same time as PERT, although the two are primarily used in conjunction with one another.

  • Critical activity is the term given to tasks which cannot over-run or take up more resources than planned for. A critical activity is, as the name denotes, critical to successful project completion.

  • Float or slack refers to the time and resources available during the project. Free float refers to the leverage in resources you have should your team hit a delay, while negative slack refers to tasks that have a deficit of resources.

  • Lead time is the time in which a predecessor event must be completed in order for an event to be reached.

  • Lag time is the soonest time an event can follow another.

  • Fast tracking is when your team decides to run critical tasks in tandem in order to shorten the overall critical path.

  • Crashing critical path means you inject additional resources into a critical path activity, thus shortening the time needed for it to be completed, making the critical path shorter.

Steps for PERT project planning

Now that you know all the key terms, here’s how to put them into practice:

  1. Identify your tasks: You should set out all the tasks needed to complete your project, which may be a bit time consuming. But, if you have a complex project on your hands, getting visibility on it at this early stage is key.

  2. Define a proper sequence: Decide the best sequence to get the optimum results from each task, remember that you can run multiple tasks in parallel. Set task dependencies in a sensible order.

  3. Estimate timings: Figure out how much time each task needs, creating an optimistic, pessimistic and expected time.

  4. Create a PERT diagram: Create a visual of your project.

  5. Assign float: Make sure you know how many resources each task will require.

  6. Critical path estimate: Based on your framework so far, set a date for total completion.

Planning tasks in PERT

A PERT table will help you record your timings and activity sequence. This isn’t only useful in planning stages, it’s also a valuable timetable you can refer back to for the whole project. Below is a PERT table example:









Start date







Staff selection







Equipment selection







Blueprint creation







Onboarding of staff







Install new equip.

B, C





Making a PERT network diagram

Once your table is made, you can create a corresponding PERT chart. This works like a flow chart to give a clear visual indication to the project sequence. You may also wish to use a digital Gantt chart. Your diagram should consist of nodes, with each node describing an activity as well as its optimistic, pessimistic, and expected times.

Here is an example of a full PERT network diagram.

PERT technique: pros and cons

As you can see, the PERT technique, even in the planning phases, is no small undertaking. You and your team should think carefully if this is the best management technique for your chosen project. Generally, the PERT approach isn’t very scalable to small projects. Plus, if you try to apply it to fairly straightforward projects, you may end up in a “too many cooks spoil the broth” situation. Consider the following pros and cons before going ahead with this method:

Pros of the PERT technique

  • Creates a clear and easy-to-understand visual on the entire project
  • Permits for in-depth analysis of project resources and performance before commencement
  • Creates a clear timeline for a structured approach
  • Helps foster accountability as everyone has clearly defined roles and timings
  • Accounts for hold-ups
  • Can motivate team members through a clear plan of collaboration
  • Can lead to quicker project completion due to everyone knowing what they should be doing and when, e.g. no hold-ups through poor communication of expectations

Cons of the PERT technique

  • Once you start breaking down every required activity, you can start reaching an overwhelming number of tasks
  • Not very applicable to smaller projects and simple tasks
  • Nodes and charts help show expectations but not the live status
  • Expectations aren’t always the reality as the project progresses
  • Dramatically increased admin during scoping phase
  • Time estimates can feel oppressive and non-conducive to creative tasks

Is the PERT technique right for you and your team?

If your project involves a lot of people and a lot of tasks, having a PERT network diagram to act as a blueprint will give everyone a strong project management tool they can use as a foundation going forward. That said, if your project isn’t all that complicated, you may just muddy the waters and waste precious time on scoping something that doesn’t need such detail.

What are the alternatives to PERT?

If you think your team can take advantage of some of the concepts of PERT without fully adopting the method, try looking for tools that encompass the same mentality with a bit less paperwork. Dropbox offers task management tools that make it easy to stay on top of what your team is doing. With app integrations including Xero, Monday, and Trello, you can manage finances, team tasks, and tackle problems easily all from within Dropbox.

Project managers may find that what a team really needs isn’t a complex planning technique so much as a clearly defined work process and the tools to achieve it.

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