Today’s companies are confronting the threat of increased complexity through a modular product architecture. The implementation of a modular structure comes with high effort, yet during the application phase these expenditures are compensated by efficient complexity handling. However, the modular structure is not permanent. Decisions on new modules and module variants have to be made, while simultaneously ensuring commonalities within the product family. When preparing such decisions, an insufficient amount of support exists to calculate with reasonable effort the complexity costs. Therefore, a new approach to examine complexity costs has been derived and subsequently tested at Bosch Thermotechnik.