This paper presents a general method for estimating the backflashover rate (BFOR) on high voltage (HV) transmission lines. The method employs a state-of-the-art model of HV transmission line (TL) for backflashover (BFO) analysis, assembled within the EMTP-ATP software package and subsequently used—with EMTP running in batch mode—to construct a curve of limiting parameters (CLP). The CLP brings into relationship incident lightning currents with critical currents for the BFO occurrence and, furthermore, provides means for estimating the BFO probability. Namely, the probability of BFO occurrence at a particular TL tower is obtained by computing the volume under the surface of the probability density function of the bivariate log-normal statistical distribution of lightning current parameters, bounded by the CLP in the appropriate coordinate space. This probability in combination with the estimated number of direct lightning strikes to TL towers—obtained from the application of the electrogeometric model—provides the associated BFOR, assuming it is further normalised on the basis of 100 km-years. The usage of the proposed method is demonstrated on a typical HV transmission line. A sensitivity study for estimating the BFOR is provided, along with results comparison between different methods.