Bending fatigue is one of the failure modes of spur gear tooth. Crack initiates at the root of a tooth on the active side. Crack due to bending fatigue results in tooth breakage. It may cause a sudden or catastrophic failure of spur gears. A major concern for design engineers is to prevent this type of failure, because it will cause accidents, casualties and financial losses. Many researchers have done excellent work on crack propagation in gears due to bending fatigue. Different crack growth models, based on the linear elastic fracture mechanics (LEFM), are used for crack propagation analysis and prediction of the service life of gears. The study in this paper includes the factorial design approach used for gear tooth bending fatigue crack propagation for specific gear configurations. Experiments are performed on the gears with optimized parameters for three different materials. Crack propagation life is estimated for these gears materials. Finite element (with Mechanical APDL 17.0) analysis for crack propagation is also done on optimized gear with SAE8620 materials.