An approach to determine a power-on-hour offset for a memory device that is newly-installed into a computer system is provided, which subtracts a current power-on-hour count of the memory device from a current power-on-hour value of a power supply that supplies operative power to the memory device within the computer system. In response to the computer system powering down, an accumulated power-on-hour for the memory device is determined by subtracting the power-on-hour offset of the memory from a current power-on-hour value of the computer system power supply. The determined power-on-hour offset and accumulated power-on-hour values are saved into one or more designated bytes of a free area of electrically erasable programmable read-only memory of the memory device that are available for data storage by a memory controller, and wherein data stored therein persists after operative power is lost to the memory device, the memory controller or the computer system.