The graduation thesis presents the verification of the existing energy performance certificate, made by the manufacturer of energy performance certificates, for a dwelling residential building in Medvode, built in 2011, with suggestions for improvement, which would ensure compliance of the building with the existing requirements for efficient use of energy. The beginning of the thesis describes the valid legislation in the field of the energy performance certificate, which is followed by a presentation of the discussed building. Based on calculations, the software KI Energija is used to make a calculated energy performance certificate according to the valid legislation and the work methodology. Through a comparison with the manufactured energy performance certificate based on calculation, the correctness of the calculations of the existing energy performance certificate, made by the manufacturer, is verified. Presented are all the errors in the calculations of the existing energy performance certificate and causes, which have led to incorrect calculations. At the end it presents the suggested measures for the improvement of the building’s energy efficiency in order for the building to meet all the requirements for an energy efficient building according to the Rules on efficient use of energy in buildings with a technical guideline (2010).