Hungary, as a member of the European Union, adapts to the EU’s climate strategy and energy policy, which includes the implementation of the Energy Performance of Buildings Directive (EPBD). The first version of EPBD was published in 2002. A recast was formulated in 2010, which were revised in 2018, and in 2024. Based on the revision of EPBD in 2018, the Hungarian national decrees had to be revised. After the COVID and the energy crisis, finally in 2023, the 9/2023. ÉKM decree was formulated, and replaced the former 7/2006. TNM decree. The new decree modified the calculation and certification methods of buildings energy performance in Hungary according to EPBD and the up-to-date European standards. The significant changes in the regulation rise the questions of how the calculation and certification results have changed, and how the building designs should change to meet the modified requirements. In this research, residential buildings were examined according to the energy calculation and certification methods defined in the old and the new decrees. Eight relatively small residential buildings were selected from the author’s architectural design praxis, and energy calculations were made in two versions, according to the two regulations using the Auricon Energetic software. The partial results of the calculation, and the final results of the certificates were compared in pairs. The differences in the results were identified, and the reasons were revealed behind them. The research can also provide useful conclusions for the architectural and building engineering design of new nearly zero energy buildings.