Accreting black holes show characteristic features that result from reprocessing of hard X-ray photons by the accretion disk. The shape of these features depends on the properties of the accretion disc and the black holes. Even though X-ray 'reflection' energy spectra have been extensively modelled to constrain the geometry of these systems and the spin of black holes, X-ray reverberation mapping lacks from the same accuracy in modelling. I present the reltrans model that aims to self-consistently explain the reverberation time lags observed in accreting black holes together with other different types of lags connected to the mass accretion rate in the disc. I show the importance of introducing a radial ionisation profile in the disk and how this can change the lag energy spectrum. I applied this model on both black hole binaries (Cygnus X-1 and MAXI J1820+070) and supermassive black holes (Mrk 335) constraining the accretion disc parameters and measuring the black hole mass.