How To Estimate Time On Any Project (with the PERT formula)

Pert Formula Thumb

Most people struggle when they’re asked to estimate the time they need to complete a project. Some people error on the side of pessimism, quoting far too much time, while others are too optimistic, leading to missed deadlines and unhappy clients.

Being able to estimate the amount of time required to complete a task is a skill that every project manager should have. In fact, project managers are almost wholly graded based on their ability to see a project to it’s timely completion.

First, You Must Identify The Task

It’s impossible to know how much time a task will require if you don’t first understand the true scope of the task. Often, projects are late not because of lack of effort, but because the details of the project were not properly identified and prioritized. Once you know the tasks, it is up to the project manager to include the necessary parties involved in the estimation process. The person who will be doing the work will always have the most accurate estimation.

Break The Project Down

When you look at a project as a whole, it’s often difficult to conduct a true analysis of the requirements. This is especially true for large projects. Breaking down your project means segmenting all of the different moving pieces into so-called “mini projects”. From there, you can allocate small portions of time to certain aspects of the project. Finally, you add together the projected time of all of the mini projects, resulting in a more accurate final duration length. By narrowing the scope to these single “events”, you will be able to provide a better overall estimate.

For an example, I will use a website project. A client contacts you and asks for you to quote him on a time span to complete his site. You could go out on a limb or reference past projects as the standard deviation. Or you could break the project down into the individual pages. “The header and footer will take two hours. The home page five. The about, services and contact page should each take about three hours each. In total, that comes to 16 hours.”

Using The PERT Formula To Make Your Time Estimates Even More Accurate

PERT stands for Project Evaluation and Review Technique. It’s a project estimation technique used by thousands of organizations around the world.

Many top organization employ mathematical formulas to estimate a task or activity. While there is some science involved, most of the effectiveness comes from the psychological effect that using a cold calculation can provide. I prefer to use the PERT formula, for it’s simplicity and accuracy.

In order to use PERT, you must first identify three simple estimates:

  1. (Tm) The Most Likely Time Required
  2. (To) The Most Optimistic Time Required
  3. (Tp) The Most Pessimistic Time Required

Now apply the following formula:

PERT Formula that you can use to provide better project estimates and cost.

Our PERT Formula Solution!

Voila! Now you have a fairly accurate estimate based on mathematical calculation, not emotion, greed or guilt.

Allen Gingrich

Author Allen Gingrich

Allen has worked on the web for over a dozen years. Like many young entrepreneurs, he began with a small workspace in his basement, where he eventually formed Ideas and Pixels. The rest, well, is history. Allen enjoys fine wines, weight training, and beautiful, semantic code.

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  • Amin Shawki

    This is a challenge a lot of people face! Interesting post Allen, I’ll have to use PERT now..

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  • shajahan

    hello sir how to estimate the maths formula project

  • medmart

    This tip is amazing thanks so much. It knocked our time in half – for our medical insurance deadlines!

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  • would love to have a math guru help alter this so we could give The Most Likely Time Required, and a confidence factor that this is the most likely time, then have it produce the real “likley time estimate”

    we have found that too many times everyone simply starts with the most likley, then cuts the most optimistic in half and doubles the most pessimistic time, thereby really making this type of formula a mute point.

  • Lorenzo Rodriguez

    Where does the “6” come from?