Calories per Day Calculator View Calculator Use your Resting Metabolism (RMR) (also known as Basal Metabolism or BMR) then factor in your activity level to get about how many calories you burn in an average day. You can eat about this many calories per day to maintain your current weight. This calculator uses gender, height, weight, and age to determine your RMR, then makes adjustments depending on the activity level you choose. Learn more about putting this calculator or other calculators on your website.