The invention relates to a device (10) for determining spatially dependent x-ray flux degradation and photon spectral change, a system (1) for determining spatially dependent x-ray flux degradation and photon spectral change for an x-ray tube (20), a method for spatially dependent x-ray flux degradation and photon spectral change for an x-ray tube (20), a computer program element for controlling such device (10) or system (1) for performing such method and a computer readable medium having stored such computer program element. The device (10) for determining spatially dependent x-ray flux degradation and photon spectral change comprises an acquisition unit (11), a processing unit (12), a calculation unit (13), and a combination unit (14). The acquisition unit (11) is configured to acquire x-ray flux degradation data for the x-ray tube (20). The processing unit (12) is configured to process the x-ray flux degradation data into spatially dependent flux degradation data. The calculation unit (13) is configured to calculate at least a photon spectral change of the x-ray tube (20) and to convert the photon spectral change into a spatially dependent spectrum. The combination unit (14) is configured to combine the spatially dependent flux degradation data and the spatially dependent spectrum.