NaI(Tl)  detectors are an important part of any radiation measurement laboratory due to highest light yield, high density, reasonable energy resolution, low cost and ease of operation. The detector response varies with incident gamma energy, detector dimensions, source-to-detector distance and source geometry. For absolute activity measurements the exact information of absolute total efficiency, absolute peak efficiency and peak-to-total ratio are necessarily to be known especially in case when mixture of gamma emitting sources are present. In this paper, we report the calibration study of NaI(Tl) detector using a point source. Monte Carlo simulation code EGS5 is used to determine intrinsic efficiency for 10⁶ incident gammas, with help of source biasing technique, and is finally converted to absolute efficiency. The variations of absolute total and absolute peak efficiencies versus energy for three different source to detector distances are presented alongwith peak-to-total ratio.