A model of a hybrid electric vehicle including an aftertreatment system is developed and validated. The model describes a vehicle with the same parallel hybrid architecture that is commonly used in commercial heavy duty vehicles and is validated using data gathered from vehicles during real world driving. The goal with the model is to describe the main dynamics of the system and give accurate estimations of fuel consumption and emissions while at the same time keeping simulation times short. The model consists of several sub components, out of which the most important ones are: combustion engine, electric motor, aftertreatment system, driveline, and vehicle chassis. The different components are interchangeable making it possible for the user to change specific components to make the model fit their needs.