The COMPASS tokamak, a mid-sized flexible device with ITER-like shape, which can operate in H-mode, is starting its re-established operation at the Institute of Plasma Physics in Prague. A new 600 kW, 40 keV neutral beam injection (NBI) system is foreseen as a major upgrade. Reported here are predictive simulations with the ASTRA transport code, in which the FAFNER Monte-Carlo NBI code is, for the first time, self-consistently integrated. These simulations are carried out for several typical COMPASS scenarios with differing magnetic fields, plasma currents and shapes. We compare Ohmic scenarios with NBI-heated scenarios and show that NBI is able to significantly improve the plasma performance, particularly to attain T i = T e , which is the primary goal of the NBI system. The NBI performance is discussed in detail. The chosen energy of 40 keV is shown to be in many aspects optimum. Simulations also predict substantial losses—orbit losses are pronounced for counter-current injection and charge-exchange losses caused by beam-halo neutrals are raised due to high NBI particle input.