Orthogonal frequency division multiplexing (OFDM) technology has been adopted in various communications and broadcasting systems, including LTE, WiMax, and DVB-T2. However, cyclic prefix (CP) and guard band are required to limit the inter-symbol and adjacent interference, which would cause loss of spectral efficiency. Filter bank multiple carrier (FBMC) technology is one of the alternative solutions of multicarrier modulation that mitigate such problems. FBMC applies offset-QAM (OQAM) and band-limited filtering on each subcarrier, which eliminates the need of CP and guard band. FBMC filtering could maintain the orthogonality in a real signal domain by using a well localized filter. However, due to the OQAM structure, the transmitted data is mixed with an intrinsic interference, therefore, conventional log likelihood ratio (LLR) calculation for OFDM system is not applicable to FBMC system. In this letter, we propose an efficient LLR calculation method for use in FBMC system. It is found that the proposed method does not increase the implementation complexity of FBMC receiver while it performs same as that of OFDM system.