With the increasing adoption of electric vehicles as a sustainable solution to curb greenhouse gas emissions, the reliability and lifetime calculation of power electronic converters, particularly semiconductor components, in traction inverters, become paramount. Utilizing a mission profile based on the worldwide harmonized lightduty test cycle, this paper introduces an advanced approach to calculate semiconductor lifetime of an EV traction inverter. Employing a functional model to calculate power losses and device temperatures. An ageing model, incorporating power cycling capability data in a LESIT model, determines consumed lifetime. The feedback loop integrates the consumed lifetime into the functional model, degrading thermal properties in proportion allowing the changing system characteristics to be taken into account during calculation. This positive feedback loop accelerates ageing, highlighting the significant influence on the lifetime assessment compared to conventional implementations.