In this paper, we present a novel semi-analytical approach to calculate first-order electron–vibration (EV) coupling constants within the framework of density functional theory. It combines analytical expressions for the first-order derivative of the Kohn–Sham operator with respect to nuclear displacements with coupled-perturbed Kohn–Sham theory to determine the derivative of the electronic density matrix. This allows us to efficiently compute accurate EV coupling constants.We apply our approach to describe inelastic electron tunneling (IET) spectra of metallic and molecular junctions. A gold junction bridged by an atomic chain is used to validate the developed method, reproducing established experimental and theoretical results. For octanedithiol and octanediamine single-molecule junctions, we discuss the influence of the anchoring group and mechanical stretching on the IET spectra.