Predicting project completion times is one of the challenges of Project Managers. Project schedule overruns are quite common due to uncertainty in estimating task durations, lack of historical data, inadequate skill, etc.

We could simply add the usual 10% schedule contingency to help ensure we finish our project on time or maybe we could take a more scientific approach based on a beta (β) frequency distribution and the PERT (programme evaluation and review technique) formula:

In this situation, the project critical path BET = (O + 4ML + P)/6 = (22 + 160 + 100) = 47 days, the Standard Deviation = (P – O)/6 = 13 days, and Contingency = Standard Factor x Standard Deviation. The Standard Factor is the same for all projects. As with all estimates, their accuracy depends on the accuracy of the input data. To … Read More »