In the coming years, electromobility will be confronted with increasing demands regarding the reliability of electrical machines. In this paper a modeling methodology is presented, which allows to estimate the reliability and lifetime of the insulation system of electrical machines. Different statistical and physical modeling methods are presented, which are transformed for the later multiple regression. The methodology of Design of Experiments (DoE) is used to describe the insulation system. Since the effort for the experimental design of the DoE varies strongly with the number of effects to be investigated and the statistical accuracy, different experimental designs are presented, which can be considered for different numbers of factors. Depending on the research question, a suitable experimental design can be selected. For the calculation of the lifetime, Miner’s rule is used in addition to the multiple regression, so that the percentage lifetime consumption due to a load spectrum can also be calculated.