Abstract: A method for estimating effort and cost to maintain a software application, group of applications or an aggregate system of applications entails determining a system size (in function points) and productivity level (in function points per hour or full-time equivalent). The productivity level takes into consideration the maintenance tasks to be performed as well as personnel attributes, such as capability and experience pertaining to the task. The effort equals the product of an effort multiplier and the system size divided by the productivity level. The effort multiplier takes into account maintenance complexities that may result in added effort and cost. The cost is determined by applying prevailing rates and fees to the calculated effort. As the maintained system is developed and enhanced, and as portions of the system are retired, the system size and productivity level are re-assessed and the effort and cost to maintain the system, as modified, are re-computed.