In this paper, we propose, as an approximation for the SINR of a precoded multicarrier system employing linear MMSE equalization, the use of the lognormal distribution with the smallest Kullback-Leibler distance to the observed SINR distribution. With this approximation, an expression for the coded pairwise error probability of this system is given. Simulation results show that the lognormal distribution matches accurately the SINR distribution. The Bit Error Rate (BER) performances with analytical computations using the lognormal approximation are very close to Monte Carlo simulations for uncoded and coded systems.