Calories are the body’s fuel reserve. We store calories as fat, and we burn that fat as we exercise.
But what if we don’t exercise? Well, the less active we are, the less fat we burn. If you aren’t very active, you would need less food than if you were very active. Still, we all burn calories every day. Even if you did absolutely nothing all day, you would still burn calories from just breathing, just having a heartbeat, just digesting food, and just thinking. Your body burns calories no matter what.
This calculator assumes that you are totally inactive all day. The result it gives you is the minimum amount of calories you burn to stay alive at your current weight. Resting Metabolic Rate (RMR) is closely related to Basal Metabolic Rate (BMR).