It is essential that the insulation system of the overhead distribution lines should be properly designed to ensure their immunity against lightning-induced overvoltages (LIOVs) caused by nearby return strokes. Therefore, accurate calculation of the peak values of LIOVs is important for the insulation design. In this paper, a formula is proposed to calculate the peak values of LIOVs for both first and subsequent strokes. The typical waveforms of the first and subsequent return strokes are adopted for this study considering a wide range of ground resistivity, from 0.25 to 20 k Omega m. The 2-D finite-difference time-domain method associated with the Agrawal coupling model is employed for the calculation of LIOVs. In addition, the effect of ground permittivity on the peak values of LIOVs is also investigated. Finally, the proposed formula is applied to calculate the annual number of flashovers per 100 km of the overhead line.