The last time you had to estimate the length of time a project would take, how reliable was that estimate? Often this is one the hardest things for people to do accurately and yet it is also one of the most important things that you can learn how to do. We need to understand how long things take whether our businesses use time estimates working directly with customers or that we simply need to be able to accurately estimate how long internal projects will take. Having this understanding will help us meet commitments to our customers, and improve our abilities to run our projects. So how can you develop a better estimate of the time that something is going to take you to do?
Use the below 3 Point Duration Estimating Approach. It is a simple equation:
(Pessimistic Time + 4 * Most Likely Time + Optimistic Time)/6 = Expected Time Estimate
Pessimistic Time: the maximum possible time required to accomplish an activity, assuming everything goes wrong (but excluding major catastrophes).
Most Likely Time: the best estimate of the time required to accomplish an activity, assuming everything proceeds as normal.
Optimistic Time: the minimum possible time required to accomplish an activity, assuming everything proceeds better than is normally expected.
An example: You own a small home remodeling company. You received a phone call this morning from one of your old customers needing your immediate assistance. During a storm the night before a tree was blown over and fell on an old customer’s house doing extensive damage to the roof. While money is a non-issue for this customer, the customer most values your ability to get the job done quickly. He presses you to give him an estimate of how long it will take to get everything corrected. You decide to use the three point duration estimating approach and determine the following times:
Pessimistic Time: Based on the severity of last night’s storm, there is a good chance that materials needed for the repair will not be on hand at your local suppliers. This means that it could take up to two weeks (14 days) for you to get the needed materials. Once you have materials on hand you may have to finish another project or at least get it to a stopping point before you can start the repairs on the roof. This could take another 2 days and actually doing the work should take no more than 2 days. So the pessimistic time would be 18 days.
Most Likely Time: You will be able to get the materials you need within three days. It will take you a day to get to a stopping point on your current project and the actual roof repair should take no more than 2 days. The most likely time would be 6 days.
Optimistic Time: You may have the material you need on hand and available at another project site. You are already at a stopping point at your current project due to the forecast of last night’s storm, and can start immediately on making the repairs to the roof. So optimistically you could have the roof repaired in 2 days.
Now let’s put that into the equation and see what an accurate estimate would be:
(18 + 4*6+2)/6 = Expected Time Estimate
(18+24+2)/6 = Expected Time Estimate
7.333 Days = Expected Time Estimate to complete. What does this mean? It means that approximately 95% of the time you would be able to complete the Project in less than 8 days. Note that on more complex and longer projects with multiple steps you would want to use this equation for each project work step and add them together to derive an overall Expected Time Estimate for the completion of the project.
Try this technique out and see if it helps you provide more accurate time estimates for both your internal and customer projects.