Runtime Aging Compensation and Calibration

An apparatus and method for efficiently updating power supply voltages due to degradation from aging. A computing system includes one or more functional units and a runtime voltage calibrator (or calibrator). The calibrator is capable of performing power supply calibration for the one or more supply voltage power rail used by the one or more functional units. The calibrator identifies a particular ground reference power rail that is received by the one or more functional units. The calibrator also identifies a first supply voltage power rail that is received by at least a first functional unit of the one or more functional units. If the runtime voltage calibrator determines that all circuitry that uses the particular ground reference power rail is idle, the calibrator performs power supply calibration for the first supply voltage power rail. The calibrator does not wait for a bootup operation and avoids interference from ground bounce.