Stellar models from accreting protostars compared to classical models. Black lines show the models originating from the accreting initial model, while blue lines show the evolution from classical initial models. The full lines correspond to a one solar mass model while the dashed lines correspond to a four solar mass model. Top left panel: Kiel diagram. Top right panel: Hertzprung-Russel diagram, where L is the photospheric luminosity. Bottom left panel: time evolution of the stellar radius. Bottom right: temperature – density (cgs units) profiles of selected models which are marked with a circle in the Kiel and Hertzsprung-Russel diagrams.