Energy is used in whatever you're doing, even when you sleep. Basal Metabolic Rate (BMR) indicates the number of calories you'd burn if you are in rest all day. Every year, it becomes harder to eat whatever you want and stay slim as you would have noticed as the BMR decreases as you age. Likewise, depriving yourself of food in hopes of losing weight also decreases your BMR, a foil to your intentions. However, a regular routine of cardiovascular exercise can increase your BMR, improving your health and fitness when your body's ability to burn energy gradually slows down. Once you know your BMR, you can calculate your Daily Calorie Needs based on your activity level using the Harris Benedict Equation.