In this paper we present a modification of an existing analytical model for a long surface crack on a conductive plate. This is actually a thin skin model and the challenge for its successful implementation is the accurate calculation of the magnetic field on the defect-free surface on a conductor. We can now combine analytical expressions with numerical results to calculate the coil impedance changes, due to the defect existence. Using the numerical results by FEM for the coil’s magnetic field into the final impedance change analytical expression we can simulate eddy current probes with complex shape that are difficult to be described analytically.