Adaptive modulation and coding is a commonly used technique to improve throughput in wireless system. Due to the delay in channel condition feedbacks, the actual channel condition may change at the time of transmission and results in capacity loss. In this paper, we establish a model to analyze the capacity loss due to channel condition feedback delay. Simulation results show that our approach is more accurate to calculate the capacity loss, compared to traditional K-step Markov approach. The results can be used to design channel update frequency adaptive to channel conditions and diversity reception.