Find out exactly how many calories your body burns at complete rest. The critical first step to understanding your total daily energy expenditure.
Your Basal Metabolic Rate (BMR) is the total number of calories that your body needs to perform basic, life-sustaining functions. These basal functions include circulation, breathing, cell production, nutrient processing, protein synthesis, and ion transport.
You can think of BMR as the number of calories you would burn if you stayed in bed all day and did absolutely nothing. For most people, BMR accounts for 60% to 75% of total daily energy expenditure (TDEE).
Knowing your BMR is the first step in calculating your TDEE. Once you know your BMR, you can apply an activity multiplier to figure out your total daily calorie burn.
Crucially, your BMR represents the minimum amount of energy your body needs to function optimally. Dieting aggressively below your BMR for extended periods can lead to muscle loss, fatigue, hormone disruption, and metabolic adaptation (where your body lowers its BMR to conserve energy).