A quantitative method based on harmonic Hall voltage analysis for measuring gate voltage-driven changes in magnetic anisotropy at ferromagnet/oxide (FM/Ox) interfaces has been developed and experimentally validated. The method involves applying an AC voltage simultaneously across the Hall bar and oxide gate using the same voltage source, measuring the first and second harmonic Hall voltage responses, and performing subsequent data analysis. Measurements conducted at high modulation frequencies primarily probe electrostatic effects while minimizing the influence of slower magnetoionic dynamics. Based on the devised method, the voltage-controlled magnetic anisotropy (VCMA) efficiency for the Co/AlOx interface is found to be approximately −40 fJ/(V m), which is in agreement with previous reports. Additionally, this approach enables the measurement of voltage-induced changes in anomalous Hall resistance. The results are interpreted using a spin-dependent screening model, which describes the experimental data remarkably well. The developed methodology applies to a wide range of materials for characterizing and optimizing VCMA and related phenomena in spintronic devices.