Beam-to-column connections are critical components in the performance of Moment Resisting Frames. Eurocode permits the use of Partial-Strength Joints (PSJs) offering the opportunity to optimize structural response by tailoring resistance, stiffness, and ductility. Despite this, PSJs remain underutilized and in any case more difficult to apply due to limited guidelines, particularly for predicting deformation capacity. Among bolted PSJs, T-stubs play a pivotal role as joint components that may govern strength and plastic deformation capacity. While the component method currently codified in EC3 part 1.8 provides a framework for analysing T-stubs, it has significant limitations, including simplified failure mode classifications, neglection of geometric and material nonlinearities, and an inability to accurately predict ultimate deformation capacity. Existing mechanical models, while potentially accurate, are often too complex for practical design purposes, highlighting the urgent need for simplified, reliable predictive formulas. This study focuses on addressing the critical gap in understanding the deformation capacity of joints, an area that remains poorly understood. We focus on the monotonic response of T-stubs under quasi-static actions conducting a parametric analysis based on a validated mechanical model. After a comprehensive review of existing literature, we propose simplified design formulas for predicting the deformation capacity of T-stubs. These formulas are derived through parametric studies and validated against experimental data from prior research. The proposed approach provides practical and accurate tools for evaluating T-stub behaviour under ultimate conditions, aiding in the design of PSJs. By improving the current methods for predicting joint deformation capacity, this work contributes to the broader adoption of PSJs in steel structures and enhances their resilience under extreme loading scenarios, such as seismic events, explosions, or accidental impacts.