This paper investigates the actual energy use for building operation with the calculated energy use according to the Danish implementation of the European Energy Performance of Buildings Directive (EPBD). This is important to various stakeholders in the building industry as the calculated energy performance is used for estimating investment security, operating budgets and for policy making. A case study shows that the actual and calculated energy use is practically the same in an average scenario. In the worst-case uncertainty scenario, the actual energy use is 20% higher than the corrected calculated energy use. More buildings should be investigated in the same manner before any sound conclusion can be made regarding whether the implementation of EPBD in a wide context leads to truly energy-efficient buildings.