A system and method for evaluating workload units in a computer system whereby each workload unit is assigned an impact number representing the number of days that the expiration date of a computer system would be changed if the workload unit were to be added or removed from the system with all other workload units remaining the same. Each workload unit may be assigned a different number for each system in the environment. The inventive system and method simplify the task of combining multidimensional workload measures and incorporate the interaction with other workload units in the system by assessing the impact on both a donor and a recipient computer systems' expiration dates. Thus, the invention provides a more robust way to measure the effect of moving workload units between systems to result in a better allocation of work amongst computer systems in a processing environment.