A method and apparatus for estimating and compensating TX LO leakage using circuitry on a loopback path connecting the transmitter and receiver are provided. The TX LO leakage may be estimated by measuring the DC signal on the receiver, measuring the phase difference between the received LO signal and the receiver LO signal, and filtering LO harmonics that may arise from the use of non-linear mixers. The DC signal on the receiver may be measured by opening and closing the loopback path, or changing the gain of the loopback path, or flipping the phase of looped back TX signal. The method may be used in an initialization or tracking calibration scheme.