Electrochemical impedance results are presented for 550 day exposures of organic‐coated carbon steel samples. Coatings consisted of translucent pigmented and unpigmented epoxy and conventional opaque epoxy polyamide systems. Coating thicknesses ranged from 20 to 185 μm. Specimens were exposed under freely corroding conditions and at two cathodic polarization levels (−850 and −1250 mV vs. SCE) in ASTM artificial ocean water. The objective was to identify impedance parameters which measure subcritical coated‐metal system property changes at early exposure times that predict significant long‐term coating deterioration. Impedance data developed at early times, including coating resistance, coating capacitance, the increase in frequency for the coating's 45° phase angle, and low frequency impedance data, are compared to the coating system's performance after 550 days exposure. Coating performance at 550 days is visually evaluated using ASTM Method D‐610, and a modification of ASTM D‐714. In particular, coating resistance, changes in the frequency for the coating's 45° phase angle, and low frequency impedance data determined at exposure times ranging from 2 to 200 days were found to predict the 550 day coating performance. Relative changes in the electrochemically active surface area were correlated with the frequency of the coating 45° phase angle.