<p>Steel structures are widely adopted in building construction because of their high strength-to-weight ratios and ease of fabrication. However, their inherent fire resistance is limited, and their structural performance deteriorates rapidly at elevated temperatures. To ensure safety, simplified design methods, such as the European Convention for Constructional Steelwork (ECCS) best-fit approach and Eurocode step-by-step procedure, are commonly used in engineering practice; however, their accuracy under varying loads and protection conditions remains insufficiently validated against high-fidelity models. This study aims to assess the reliability of these simplified methods by benchmarking them against a validated finite element (FE) model of simply supported steel beams exposed to the ISO 834 standard fire. Both the unprotected and fire-protected configurations were analysed for load ratios (<i>r</i>_<i>load</i>) ranging from 0.1 to 0.5. The FE model incorporated temperature-dependent material properties and geometric and material nonlinearities and was validated against published benchmark results. The fire resistance, expressed as the time to failure based on an L/20 deflection limit, was compared with the predictions obtained using the ECCS empirical correlations and Eurocode energy-balance approach. The results show that both simplified methods are generally conservative, with the Eurocode step-by-step procedure providing a closer agreement with the FE results, particularly for protected beams. Conservatism was most pronounced at low load ratios for unprotected members, where the simplified methods underestimated the failure times by up to 80–90%. The findings provide practical guidance on the applicability and limitations of simplified methods and highlight scenarios in which a detailed numerical analysis is warranted for performance-based fire designs.</p>