In this paper, an approach is proposed to estimate the Bit Error Rate (BER) in a Wavelength Division Multiplexing (WDM) receiver with component crosstalk considering all possible bit combinations in the interfering channels instead of the usual worst-case approach. In addition, probability density function (pdf) and bit error rate (BER) with finite interferers are studied using a new mathematical formulation based on Maclaurin series expansion of the N-th power of zero order Bessel Function. This analysis results in more realistic estimation of BER and optimum detection threshold for minimum BER than that obtained using worst-case study. The improvement in accuracy of estimation of BER with the present approach over the worst-case approximation approach is more for higher crosstalk level and large number of interfering channels. © 2017 Elsevier GmbH