The paper examines how geometric design parameters affect crankshaft fracture due to fatigue using the finite element method. It explores the influence of the fillet radius on the crankpin journal, the shape of the grooves on the splined shaft, and their interaction on the crankshaft's fatigue behavior. Using known material properties and operating loads, a CAD/FEM model of the crankshaft was created, and a structural analysis was performed. Based on these results, critical points on the crankshaft were identified, followed by fatigue analysis and lifespan evaluation. Numerical simulations showed that increasing the fillet radius on the crankpin journal significantly reduces stress concentration and boosts the crankshaft's fatigue life. Altering the geometry of the grooves on the splined shaft redistributes stress and moderately extends its lifespan. The best results came from combining both geometric changes, demonstrating the synergistic effect of optimizing design parameters. These findings can serve as valuable guidelines for designing crankshafts to minimize fatigue failure risks and enhance their operational reliability.