A novel magnetic approach is introduced to measure the corrosion rate of bare and coated ferromagnetic materials. The corrosion of bare and acrylic-coated cobalt is monitored in situ and in real-time by coupling electrochemical impedance spectroscopy (EIS) and saturation magnetic moment measurements using a vibrating sample magnetometer (VSM). For the first time, the corrosion rate beneath a polymer coating is measured accurately in situ; additionally, it is suggested that the VSM can be used to enhance the interpretation of EIS data.