Modeling Resource Loads
The basic building block of modeling resource utilization and capacity is to be able to accurately model the loads placed on your resources. The first impulse may be to simply sum all of the tasks assigned to a resource to determine their load; after all, isn't that what all of those detailed project work plans are for? Unfortunately, this technique is very costly as, instead of leading projects, project managers are now in the clerical position of tracking down the status of every single task and ensuring that every single task's level of effort is precise.
Loading with this the level of granularity becomes time consuming as it is difficult to decide whether a task will take 1.5 hours or whether it will actually be closer to 2.0 hours. Ironically, determining resource loads with a bottom-up, task-oriented approach is not only very costly, but in the end, is very inaccurate also. Successful leaders see this as a non-value add method of resource loading and the added detail is not worth the effort.
Rather, for the purposes of portfolio planning, the value-based approach of resource loading is best done top-down - at the project level. The ability to estimate is fundamental to project management and any technical profession. For each resource on each project, an estimate of the overall percentage of a resource's time that will be committed to that project during a given time frame.
That is the proper level of accuracy necessary for the purposes of portfolio planning and resource utilization. Typically, percentage estimates such as 25%, 35%, or 50% are within the margin of error for resource utilization purposes. The end result is a resource utilization model that is not only easier and less time consuming to manage, but more reliable as well.