The standard method of dark-matter (DM) relic-density calculation is based on solving the Boltzmann equation for the number density and relies on the assumption that DM particles are in thermal equilibrium with the SM plasma or a secluded thermal equilibrium in the dark sector is maintained. The interplay of different interactions in some DM models can lead to a deviation of the DM energy distribution from the equilibrium shape before the relic abundance is established and this deviation can have a considerable impact on the predicted amount of DM in the Universe. In my talk I am going to outline more elaborate approaches to calculating the distribution function of DM particles (and the corresponding DM number density) and consider a few examples.