Project Management

Task Duration Estimation: A Simple Solution

Kevin is an engineer in Calgary, Alberta.

This article and its accompanying template describe how to use a simple spreadsheet to make a reasonable best guess of the likely duration of a given task. You would do this if you don't have much experience with a particular task but you have a rough idea how long it ought to take—and you want to make sure you provide enough time in the schedule that the task has a reasonable chance of occurring on time without negatively affecting the rest of the project.

Project managers might do this with specialized software, but anyone can do the same thing with just a spreadsheet. The spreadsheet makes its estimate by substituting a Monte Carlo simulation in place of actual project experience. It simulates 5,000 similar projects that vary randomly within the given bounds of duration, thus encounter varying degree of performance (shorter and longer duration than expected).

The simulated project durations vary according to a very simple probability distribution known as "triangle distribution," which consists of three points:

  1. The first point (low) is the best possible outcome, the fastest possible time that the task could be done in.
  2. The second point is the most likely estimate that the task would take. This is your best guess you would use if you were not conducting a simulation.
  3. The third point (high) is the worst possible outcome, the …

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