Hybrid reinforcement systems, combining steel and FRP (Fibre-Reinforced Polymer) rebars, offer an innovative solution for enhancing the strength and ductility of concrete beams. By integrating the mechanical properties of both materials, this approach ensures improved performance compared to beams reinforced solely with FRP, particularly in terms of deformability and ductility. The combination of steel and FRP reinforcement also mitigates the corrosion-related issues typical of traditional steel-reinforced concrete. However, despite these advantages, there is still a lack of comprehensive understanding regarding the behaviour of hybrid reinforced beams under service condition. Although several studies were carried out on concrete beams reinforced with hybrid systems, the specific parameters governing the deflection response under service loads remain inadequately defined in the current literature. This limitation makes difficult the development of reliable predictive models for deflection in hybrid-reinforced concrete beams. The objective of this study is to address these gaps by evaluating and calibrating existing design models to better predict the deflection of hybrid-reinforced beams. Experimental data obtained from bending tests on 55 hybrid-reinforced beams were analysed to assess the accuracy of current theoretical models (initially proposed for FRP reinforced beams), specifically those available in ACI 440-22 and CNR-DT203/2006 guidelines. The results obtained highlight the limitations of these models in predicting the deflection of hybrid systems, with a high percentage of specimens exhibiting underestimated deflections. In this context, to improve prediction accuracy, corrective parameters were introduced to the current model, leading to a significant enhancement in the accuracy of the models.