This paper describes an analysis-based method for optimizing the timing of decisions regarding early termination of block matching (BM) in the application of a successive similarity detection algorithm (SSDA). Although the SSDA reduces BM computational costs, making decisions to terminate BM or not consumes additional processor cycles. Here, total costs, including cycles for decisions, are formulated through use of a decision interval, processordependent cost factors, and a function which gives probabilities of BM termination. The optimal decision interval is derived by minimizing the cost function. Experiments on MPEG-4 video coding show the proposed method facilitates comparative evaluation of the computational costs of SSDA-based BM for various processors.