In clinical nutrition practice, energy estimation often centers on resting and total daily energy expenditure. However, alternative equations may be more appropriate when evaluating weight changes, energy availability for physical activity, or nutritional needs in critically ill individuals. This chapter explores the application of specialized formulas, including the ideal body weight (IBW) via the Devine formula, desired body weight, and the energy availability equation as complementary tools in nutritional assessment. Despite ongoing evaluation of their validity and reliability in the general population, these methods can enhance energy and macronutrient recommendations. Used in conjunction with standard equations, they provide a more comprehensive framework for clinicians seeking to optimize nutritional strategies across diverse patient populations.