A system and method are provided for determining processor usable idle time in a system employing a software instruction processor. The method establishes an idle task with a lowest processor priority for a processor executing application software instructions, and uses the processor to execute an idle task. The method ceases to execute the idle task in response to the processor executing application software instructions. The amount of periodic idle task execution is determined and stored in a tangible memory medium. For example, idle time amounts can be determined per a unit of time, i.e. a percentage per second. In one aspect, the method generates an idle task report. The report can be a periodic report expressing the duration of idle task execution per time period, or a course of execution report expressing idle task start times, idle task stop times, and durations between the corresponding start and stop times.