Aspects of a method and system for calibrating group delay errors in a combined GPS and GLONASS receiver are provided. The combined GPS and GLONASS receiver may be enabled to receive both GPS signals and GLONASS signals. GPS based navigation information may be calculated based on the received GPS signals. Group delay errors resulted by the received GLONASS signals may be calibrated based on the GPS based navigation information. Respective GLONASS signals may be estimated in responsive to the GPS based navigation information. Corresponding clock information associated with the estimated GLONASS signals may be transferred from the clock information of the GPS based navigation information. A calibration signal may be generated by comparing the estimated GLONASS signals with the received GLONASS signals. The calibration signal may be processed by an error state Kalman filter and may be used to offset the group delay errors in the combined GPS and GLONASS receiver.