By regulations on energy efficiency from 2011, the simplified methodology for calculating solar gains has been defined by the adopted values of solar radiation for whole of Serbia. This paper presents two different methods of solar gains calculation, with the support of the software package KnaufTerm 2, which relies on existing regulations in Serbia, and Ecotect software package, intended for 4-D simulations. The problem has been analyzed in the case of a residential building in Belgrade, by calculating solar gains obtained through one window, for 36 different orientations. Different orientations of the window have shown significant variations in the obtained results, which have been ignored by the rulebook, be-cause it defines only 4 orientations. By this, it was established that four... more orientations have to be defined by regulations, with separate values of solar radiation for each position. As the differences in solar gains are most visible in the east, and deviate up to 61%, in the paper then was analyzed calculation method of shading for eastern orientation, which is defined by the rulebook on energy efficiency through a variety of shading factors. The analysis has shown that the methodology defined in the regulations has given drastically lower levels of solar gains at the shaded positions, where the most visible differences were observed in the presence of three shading elements. Also, it is necessary to reconsider the values of the defined shading factors, which are, as showed by 4-D simulations, oversized.