Background: Individuals with hemiparesis exhibit decreased limb loading onto the paretic limb which is negatively associated with walking and balance ability. Decreases in hip abductor strength and delayed hip abductor moments are also associated with diminished limb loading in this population. Additionally, the paretic (affected) foot is often placed more laterally during walking which likely decreases the limb loading force. Overall, this evidence indicates that the hip abduction moment and foot placement are likely limiting factors to limb loading ability. The aim of this study was to construct and validate a biomechanical model using frontal plane variables to predict peak limb loading in older adults and individuals post-stroke. Methods: Older adults (n = 18) and individuals post-stroke (n = 22) walked on a treadmill at their self-selected speed. A biomechanical model was constructed in older adults using the hip abduction moment, center of mass (COM)-foot angle (estimated ground reaction force angle), and the ground reaction force (GRF) moment arm (horizontal distance between the hip joint center and COM) and was subsequently validated in individuals post-stroke. Findings: The model accurately modeled limb loading with three frontal plane gait characteristics explaining 86% and 59% of the variance in limb loading force in the paretic and non-paretic limbs of individuals post-stroke, respectively. Individuals post-stroke were observed to have smaller hip abduction moments and COM-foot angles compared to older adults. However, the GRF moment arm was only smaller in the non-paretic limb compared to older adults, whereas the VGRF was only smaller in the paretic limb compared to older adults. Conclusion: This model can be used to explain the mathematical relationships between the hip abduction torque, foot placement, and limb loading. Future studies may apply this model to quantify the relative contribution of each biomechanical factor to the limb loading force. This will enhance our understanding of the mechanisms of limb loading and provide the framework for designing effective rehabilitation strategies that target limb loading ability, ultimately improving balance and mobility outcomes post-stroke.