With the increasing electrification of tractors, the demand for robust frame designs capable of withstanding applied loads has grown significantly. This study focuses on determining design loads for tractor frames and predicting their fatigue life. Design loads were established by recording accelerations exerted on tractor axles during merry-go-round testing. These recorded accelerations, combined with a four-post road simulator employing the virtual iteration method, were used to derive precise design loads. The rain flow counting method was then applied to determine the load spectrum affecting critical points on the frame. Equivalent stresses at vulnerable sections were calculated, and cumulative damage was evaluated using Miner’s rule to estimate fatigue life. The analysis revealed that the cumulative damage sustained over the manufacturer-specified lifespan is ∼5.492%. This result confirms the adequacy of the pre-designed frame’s fatigue life, demonstrating its resilience and durability under operational conditions. Unlike previous studies, this research integrates merry-go-round testing, four-post road simulator simulation, and multi-flexible-body dynamics analysis to establish a comprehensive methodology for evaluating fatigue life in electric tractor frames. This novel approach enables accurate load estimation and enhances frame durability assessment, contributing to the advancement of agricultural machinery design.