Maintaining balance is a critical aspect of human gait, especially for individuals with balance deficiencies. Accurate assessment and monitoring of balance are essential to reduce the risk of falls and improve mobility outcomes. Individuals with balance impairments tend to adopt larger step widths, resulting in increased mediolateral center of mass displacement with increased step-to-step variability. We aim to establish a quantitative metric that can accurately detect balance deficiencies, potentially improving the safety and effectiveness of lower limb exoskeletons. Using the linear inverted pendulum model, we estimated the mediolateral center of mass displacement in three healthy subjects walking with narrow, normal, and wide step widths. Our analysis demonstrates the importance of mediolateral center of mass displacement for assessing balance and stability during walking showing the significant differences in this metric with varying step widths. By leveraging this metric, we aim to enhance the balance assistance with lower limb exoskeletons.