Method, system and software code for calibrating a rail track circuit comprising a plurality of rails coupled to form a track section having a predefined length, a transmit processing unit coupled to the track section at a first end of the track section, and a receive processing unit coupled at the second end of the track section. A transfer function between a transmit voltage applied by the transmit processing unit at the track section and a resulting receive current detected at the receive processing unit is first determined and then applied to the rail track circuit for automatic initial calibration or recalibration.