PERT & Project Schedules

Happy Monday and Welcome to this week’s installment of Kelly’s Contemplation.  As you know, I strive to have a balance of posts on the emotional & technical aspects of leadership & project management.  This week, I am going to focus on a more technical aspect of project manager…developing the project schedule, specifically identify durations.

I was recently speaking with some colleagues with regards to project overruns (costs and schedule) and found out that most don’t get into a PERT analysis when developing their schedules.  For the most part, they ask the SME (subject matter expert) how long they need to complete a task or series of tasks and then add a day/week and move on.  Some will ask what are the risks to getting to the deadline and help mitigate those risks, but few mentioned they go through the best, most likely, pessimistic with their teams.

PERT (Program Evaluation and Review Technique) takes a slightly skeptical view of time estimates made for each project stage. To use it, estimate the shortest possible time each activity will take, the most likely length of time, and the longest time that might be taken if the activity takes longer than expected.

Use the formula below to calculate the time to use for each project stage:

Optimistic + (4 x Most Likely) + Pessimistic/6 = Duration

How many of you leverage this tool/technique when creating your project plan?  If not, is it because your team wouldn’t spend the time giving the inputs? Do you feel the technique lacks value?


Below is a series of steps with a slide show and gallery (however you prefer to view) how to leverage MS Project for a PERT analysis. The last screen shot on the slide show is an Excel Template I setup for a friend that has zero budget for a PM tool. (still very useful)

  1. Create Your WBS
  2. Enable the PERT Toolbar
  3. Click on “PERT Entry Sheet”
  4. Enter the Optimistic, Expect, and Pessimistic Durations
  5. Click “Calculate PERT” and then say OK
  6. The durations will populate …
  7. Go back to the Gantt View, by clink View & selecting Gantt Chart
  8. Now you can work from a more confident standpoint with regards to your schedule..
  9. No Budget for tools, leverage a basic MS Excel Template to implement a PERT analysis.

This slideshow requires JavaScript.

For some this will be basic and others use some other techniques, but for some this may be brand new to you and I hope you find it useful.  I would love to hear your thoughts on this or any other key techniques you leverage when establishing durations on your project.


10 thoughts on “PERT & Project Schedules

  1. This is often a fantastic blog, could you be interested in making time for an interview concerning just how you designed it? If so e-mail me!

  2. Actually Kelly, PERT presents not a skeptical view but an over confident view of the programs probability of completing “on or before” a date. Up to a 27% bias in forecasting dates. Dates to the “left” of the actual probabilistic dates.
    Start with PERT Completion Times Revisited

    There are some reasons to use PERT. But without understanding the built in biases, you’ll get numbers that are not representative of the actual underlying statistics. Just two of the major issues:

    1. Rarely if ever, the standard deviation equal to the value used in PERT
    2. PERT assumes the statistical independence of the tasks – this is rarely the case in practice.

    1. Glen:

      Thank you so much for taking the time to visit and I am honored you took the time to comment and share the link. I would say 18 out 20 PMs I asked, don’t even use PERT and 100 out of 100 team members don’t like when I ask them to provide the 3 parameters…lol Do you find it difficult to get buy-in from the team members? Or is it like most things…if the leader shows confidence and value, the team will buy-in?

      I love your blog over at

      Thanks again for posting!


  3. Hi Robert,

    This is a great tip for anyone involved in the project management space. It amazed me the amount of PM’s who used to bring me schedules that facilitated 100% working time, no holidays, no natural disasters, no planning around resource availability in any shape or form.

    Over time, this came down to two things. Firstly, when a PM was new to the game and had to learn that things don’t go according to the plan when the plan is not framed correctly. Secondly and unfortunately more frequently, was the inability of the PM to convince senior mgmt that reducing the timelines without re-scoping was not possible!!

    In my timeline calculations I always used PERT and it works!!

    Thanks for sharing

    1. Barney, thank you so much for joining the conversation!

      Your point “unfortunately more frequently, was the inability of the PM to convince senior mgmt that reducing the timelines without re-scoping was not possible!!” was difficult for me early on in my career also.

      A strong mentor and supportive manager is crucial for young PMs.


  4. Why are projects doomed for failure (some projects)? I believe it is because like many of my colleagues in this example and in the past (and myself in the past), we have not fully leverages the tools of the trade. Very few utilize PERT, little know about Earned Value, and some have never done a stakeholder analysis.

    I have another post “The Project Failed…We Haven’t Even Started!” in which folks have pushed back, saying the template I lay out is too long, too complex. I am a firm believer in preperation and if you don’t have a good charter, understand who the players are (and their influence), what the requirements are, and have string duration estimates then Yes, your project is doomed for failure.

    President Abraham Lincoln said “If I had 6 hours to chop down a tree, I would spend 5 sharpening the axe” (something close to that). That is a perfect quote for all projects. I may spend some extra time on Project Initiation and Plan, but I haven’t a late project in over 3 years.

    Thank you so much for your post Laura!

  5. Use this tool to help:

    Good post. I’m surprised, though. We see all these what I previously thought of as “dooms-day” posts about how 99.9% of projects fail or are late, and I thought that yeah, I know lots of people who deal with this, but it can’t be this bad. The question was, WHY? Your post was enlightening because if you don’t manage and mitigate risk, you’re in big trouble. If you don’t even consider it, wow. Your project is a self-fulfilling prophecy of doom!

    Laura Gideon
    Steelray Software

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