Abstract: Examples provide a method for clock calibration. A wireless communication device includes a first clock and a second clock. The first clock is turned off but the second clock runs during the inactive state of the wireless communication device. A frequency offset of the first clock is measured with respect to a reference frequency based on a signal received from a network. A virtual timer, which is a software-based timer is updated based on the frequency offset. A drift of the second clock is measured over a predetermined time interval based on the virtual timer. The virtual timer is restored based on the drift after wake-up from the inactive state. Alternatively, a clock frequency relation between the first clock and the second clock may be measured and a phase locked loop (PLL) may be controlled based on the measured clock frequency relation.