An optimal idle state of a processor is selected using dynamically derived parameters. For example, the idle state is selected from a group of possible idle power states. A current detector is arranged to perform power measurements of the processor and to report a total power consumption of the processor for each time value of a range of discrete values for each possible idle power state. A calibration unit is arranged to communicate with the current detector and the processor, and to automatically activate a calibration sequence that is used to produce data from which idle power state is optimal for the processor for an estimated idle period.