1. electrostatic interactions of the ion within the empty host structure (i.e., based on the electrostatic field in the host structure before inserting the ion); 2. polarization at the intercalation site (i.e., electronic relaxation after inserting the ion into the host); 10 and, 3. (limited) elastic contributions (i.e., ionic relaxation, usually preserving the framework type). The electrostatic contribution is especially important for two reasons. First, electrostatics are known to be the main force holding an ion in an oxide material at a given site. This enables us to compute a first-order estimate of the intercalation migration barrier on the basis of electrostatics alone. Second, the electrostatic potential can be readily and accurately determined for the considered host systems by electronic density functional theory (DFT) calculations, providing a simple route to barrier estimates. As the ion size influences the intercalation behavior, the central question that arises is the following: how do we account for the finite ion size when the electrostatic potential is typically calculated for an infinitesimal small test particle? Here we systematically investigate the possibility to electrostatically estimate Mg migration barriers in typical ionic intercalation hosts (predominantly transition metal oxides). As such barrier estimates are usually derived from computationally intensive DFT-coupled rare events methods, a simple electrostatics-based metric presents an appealing, less computationally demanding alternative. We therefore developed the Potential of Electrostatics Finite-Ion Size (PfEFIS) framework, which combines readily computable DFT-derived electrostatic potential data with finite-size ion models and a zero spring-constant living elastic-band algorithm.