The load-carrying capacity of shafts is an important feature in the design and performance of machinery. This paper presents a comprehensive study aimed at understanding and quantifying the influence of geometry factors, including shaft diameter and the position of load between shaft supports, on the shaft’s load-carrying capacity. The load-carrying capacity criterion is the fatigue safety factor. This paper offers a systematic exploration of the influential geometry factors affecting shaft load-carrying capacity, individually and in combination. The paper concludes by considering the simultaneous influence of all the aforementioned factors. A new factor is introduced, representing the effect of geometry parameters. This factor allows for a holistic approach to shaft design, enabling engineers to make informed decisions that maximize load-carrying capacity with the changing geometry of shafts.