The research presents an efficient computation of optimal tool-length for 5-axis mold and die machining. The proposed procedure analyzes input NC data generated by a commercial CAM system and computes the minimum feasible tool-length via slight modification of tool orientation at the selected NC blocks where tool-length reduction is required. The test result shows that the research is especially useful in five-axis machining steep wall features of deep cavities in an injection molding die. The developed system is used at a domestic molding die manufacturing company.