Methods for estimating a distance between an originator and a transponder, methods for calculating a fine time adjustment in a radio, computer-readable storage media containing instructions to configure a processor to perform such methods, originators used in a system for estimating a distance to a transponder, and transponders used in a system for estimating a distance to an originator. The methods utilize fine time adjustments to achieve sub-clock cycle time resolution. The methods may utilize offset master clocks. The methods may utilize a round-trip full-duplex configuration or a round-trip half-duplex configuration. The method produces accurate estimates of the distance between two radios.