Gamma-ray detectors are widely used in many fields like environmental measurements, medicine, space science, and industry, where the detector geometrical, total, photopeak efficiencies and peak-to-total ratio could be required. The calculation of the detector efficiency depends mainly on the value of the geometrical efficiency, which depends on the solid angle subtended by the source-detector system. The present work introduces a direct analytical method to calculate the geometrical and total efficiencies of CdZnTe gamma-ray detector using off-axis isotropic radiating γ-ray [point, disk, and cylindrical] sources. To test the validity of the present work, the results are compared with some published data and also to prove how much it is important to determine the efficiency of difficult gamma-ray detection arrangement.