Solar gain is one of the driving factors for the design of ultra-low energy buildings in all climate zones. Most building simulation models and the old methodology to compute energy demand and peak loads for passive buildings does not consider self-shading and only takes shading from surrounding elements into account in a very simplified way. This leads to design decisions which are not cost effective and can cause comfort and overheating issues. This paper will introduce a new method developed to compute monthly shading factors per window. The new method takes into account all shading interactions and is based on a geometrical representation of all elements that shade transparent building envelope elements. It is implemented in the PHIUS certification software WUFI® Passive and applied to a range of existing certified passive projects. The resulting energy demands and loads are compared to the values from the previous method to compute shading impact in passive house energy balance calculations. It was found that changes in heating and cooling energy demand as well as in peak loads are significant - up to 15-20%. The paper will summarize guidance to use and fully utilize the capabilities of the new shading model in WUFI® Passive. The new method is faster but more accurate with plausible results closer to real solar gains. Application of the method will lead to more cost effective and comfortable solutions, and quicker modeling.