The calibration of high-purity germanium gamma-ray cylindrical detectors using bar (parallelepiped) sources is carried out analytically using the probability correction approach. Improved expressions for the source self-attenuation coefficient have been included in the present algorithm based on the accurate calculation of all possible path lengths covered by the gamma ray inside the bulky source. Moreover, the full-energy peak attenuation coefficient μp is included in the present algorithm. The sources were positioned at long distances from the detector window so that the coincidence summing effects could be neglected. Remarkable agreement between the measured efficiency values and the corrected efficiency values calculated by the present technique was observed. The percentage relative differences for the results calculated in this way from experimental values are at least 25% smaller than those observed and reported by the direct mathematical method in previous work.