Abstract: A method and apparatus for measuring an elapsed time from a starting signal to an ending signal in a time-to-digital converter. Primarily, the invention calculates an amount of complete cycles from the starting signal to a starting edge of a next clock cycle or the next Nth clock cycle (N is a natural number great than one) after the clock cycle corresponding to the ending signal. The amount is multiplied by a cycle time of the coarse clock to obtain a coarse time value. A time residue is calculated from the ending signal to the starting edge. Finally, the time residue is subtracted from the coarse time value to obtain a required time.