While modern buildings are becoming more and more complex, several scientific studies have uncovered performance gaps between the simulated and actual performance in buildings. Research has uncovered gaps for energy, indoor climate, user satisfaction, facility management and maintenance cost. These gaps are highly relevant for the field of building performance simulation, as large gaps make simulation results less trustworthy. Collaborators Skanska Norway, Piscada and Simenergi have since 2019 addressed this topic through research and innovation and are now close to launching “SmartTune” - a commercially available tool for creating digital twins for energy performance. The tool matches and combines measured data from the building automation system, simulated data from the SIMIEN energy simulation software and subjective assessments of indoor climate collected through a novel method for user feedback in a common, web-based interface. This article presents the goals, general concept, strategy, and overall architecture of the SmartTune system as well as plans for future development. Arguments for why digital twins are the “way forward” for building simulation are presented, and arguments for the use of advanced tools such as machine learning are discussed.