Software Project Estimation Part 3: The Cone of Uncertainty

This post is part of my series on Software Project Estimation:

The Cone of Uncertainty is another point that is very important to understand when trying to come up with an estimate for the execution of a software development project.  I originally planned on going pretty deep into the topic, but I found an article online that does a better job at it.  So, I’m going to cover it at a high level and then point you to that other article.

Early on in the project, very little is known about the detailed functional requirements and exactly how the solution is going to be constructed. Because of this lack of information, you need to understand that your estimate could be off by a certain percentage. As the project progresses, more is known about it so estimates get more accurate.

The following shows the amount of variance in estimates in different phases of the project:

  1. Scoping: -50% to +100%
  2. Requirements: 20% -33% to +50%
  3. Design: 20% to +25%

There are, however, techniques that can be utilized while putting together your esitimate that can help to make it more accourate.  In the following posts I’ll be addressing several different estimation techniques.  Each have their pluses and minues and are more appropriate at different phases of the project.

A very good article on the Cone of Uncertainty can be found on the Construx website here.

Many people have been emailing me asking about the estimation techniques that I am going to cover.  I’ll begin diving into those in the next post.  The first one will be ‘Expert Judgement’.


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