Accurate estimation of energy requirements is essential for effective nutritional assessment and intervention, particularly in diverse populations. This chapter explores the variability and limitations of commonly used predictive equations including Harris-Benedict, Mifflin-St. Jeor, Owen, Schofield (FAO/WHO/UNU), Henry Oxford, Katch-McArdle, and Cunningham. The information emphasizes the importance of selecting equations based on population-specific characteristics such as body composition, gender, and activity level. Additionally, it addresses the historical context and demographic limitations of foundational datasets, such as the Schofield database, and introduces the Henry Oxford equation as a more contemporary alternative. These insights support a more nuanced, individualized approach to energy estimation in clinical and performance nutrition settings.