Loop-back is a desirable test set-up for RF transceivers for both on-chip characterization and production testing. Measurement of IQ imbalances (phase mismatch, gain mismatch, DC offset, and time skews) in the loop-back mode is challenging due to the coupling between the receiver (RX) and transmitter (TX) parameters. We present an analytical method for the measurement of the imbalances in the loop-back mode. We excite the system with carefully designed test signals at the baseband TX input and analyze the corresponding RX baseband output. The derived and used mathematical equations based on these test inputs enable us to unambiguously compute IQ mismatches. Experiments conducted both in simulations and on a hardware platform confirm that the proposed technique can accurately compute the IQ imbalances.