What is Basal Metabolic Rate (BMR)?
Your Basal Metabolic Rate (BMR) is the number of calories your body requires to perform its most basic life-sustaining functions. These include:
- Breathing
- Circulating blood
- Controlling body temperature
- Cell growth
- Brain and nerve function
Think of BMR as the amount of energy you would burn if you stayed in bed all day without moving. It accounts for about 60% to 75% of the total calories you burn every day.
Formulas: Mifflin-St Jeor vs Harris-Benedict
This calculator lets you choose between two primary equations:
- Mifflin-St Jeor (Recommended): Developed in 1990, this is currently considered the most accurate equation for establishing BMR estimates in modern populations. It is the standard used by the American Dietetic Association.
- Harris-Benedict (Revised): Originally created in 1919 and revised in 1984. It tends to overestimate BMR in overweight individuals but is still widely used in clinical settings.
Why Knowing Your BMR Matters
Whether your goal is weight loss, weight gain, or maintenance, your BMR is the starting line.
- For Weight Loss: You should never eat below your BMR without medical supervision. Consuming fewer calories than your BMR can slow down your metabolism and cause your body to break down muscle tissue for energy.
- For Muscle Gain: To build muscle, you typically need a calorie surplus. Knowing your BMR helps you calculate your Total Daily Energy Expenditure (TDEE) so you can eat enough to fuel growth without gaining excessive fat.