This paper presents a codeword metric calculation scheme in two step joint decoding of block coded signals in an overloaded multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system. In the previous literature, the two step joint decoding scheme has been proposed for the complexity reduction of joint maximum likelihood decoding in the overloaded MIMO system. However, the two step decoding scheme has not been combined with an outer code. The selection of the candidate codewords in the inner block code may not always be able to provide the metric of a binary coded symbol for the outer code. The metric of the binary coded symbol calculated in the first stage is used in the proposed scheme. It is shown that the proposed two step decoding scheme shows better performance than a bit flipping based scheme and reduces the complexity by about 0.013 for 4 signal streams with the cost of bit error rate degradation within 0.5dB.