The calculator below estimates your Resting Metabolic Rate (RMR) using the Mifflin-St. Jeor equation and your weight, height, and age. Your RMR is the largest contributor to your Total Daily Energy Expenditure (TDEE), the theoretical estimate of how many calories your body burns each day.
The Mifflin-St. Jeor equations are not perfect, but they have been shown to be the most accurate relative to other popular RMR formulas. (See, for example, Frankenfield, D. et al., “Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review,” Journal of the Academy of Nutrition and Dietetics, Volume 105, Issue 5 (2005), pgs. 775–789.)