Introduction
Your basal metabolic rate (BMR) is the number of calories your body burns each day just to stay alive. Even when you sleep, your body uses energy to breathe, pump blood, and keep your organs working. Knowing your BMR helps you understand how many calories you need to eat each day to lose weight, gain weight, or stay the same.
This metabolic rate calculator estimates your BMR using three trusted formulas: Mifflin-St Jeor, Revised Harris-Benedict, and Katch-McArdle. Just enter your age, sex, height, and weight. The calculator also shows your total daily energy expenditure (TDEE), which factors in how active you are. You get a step-by-step breakdown of the math, a comparison table for six activity levels, and a chart so you can see your results at a glance. For a dedicated TDEE breakdown, try our TDEE calculator.
How to Use Our Metabolic Rate Calculator
Enter a few details about your body below. The calculator will show your basal metabolic rate (BMR) — the number of calories your body burns at rest each day. It also shows how many calories you need based on how active you are.
Pick your unit system. Choose US/Imperial for feet and pounds, Metric for centimeters and kilograms, or Other Units for stones and centimeters.
Enter your age. Type your current age in years. The calculator works for ages 15 to 80.
Select your biological sex. Choose Male or Female. This matters because men and women burn calories at different rates.
Enter your height. If you chose US units, type your height in feet and inches. For Metric or Other Units, type your height in centimeters.
Enter your weight. Type your weight in pounds, kilograms, or stones depending on the unit system you picked. If you are unsure whether your weight falls in a healthy range, our BMI calculator can help you check.
Enter your body fat percentage (optional). This field only appears if you select the Katch-McArdle formula in Settings. If you know your body fat percentage, type it here for a more accurate result. If you are unsure of your body fat percentage, use our body fat calculator to get an estimate.
Choose your BMR formula in Settings. Mifflin-St Jeor works best for most people. Revised Harris-Benedict is a classic option. Katch-McArdle is best if you are lean or athletic and know your body fat percentage.
Choose your energy unit in Settings. Pick Calories (kcal) or Kilojoules (kJ) to change how your results are displayed.
Click "Calculate" to see your BMR, a full step-by-step breakdown, and a table of daily calorie needs for six activity levels. Click "Reset" at any time to start over with the default values.
What Is Your Basal Metabolic Rate (BMR)?
Your basal metabolic rate, or BMR, is the number of calories your body burns each day just to stay alive. Even when you sleep, your body uses energy to breathe, pump blood, grow cells, and keep your brain working. BMR measures that baseline energy use. You can also explore our dedicated BMR calculator for an alternative look at these same formulas.
Think of it this way: if you stayed in bed all day and did nothing, your BMR is the fuel your body would still need. For most people, BMR accounts for about 60% to 75% of total daily calories burned.
What Affects Your Metabolic Rate?
Several things change how fast or slow your metabolism runs:
- Body size: Bigger bodies need more energy. People who weigh more or are taller tend to have a higher BMR. You can check whether your weight is proportional to your height with our ideal body weight calculator.
- Muscle mass: Muscle burns more calories than fat, even at rest. This is why athletes often have a higher metabolic rate. Our lean body weight calculator can help you estimate how much of your weight is lean mass, and the FFMI calculator lets you see how your muscle mass compares to others.
- Age: Metabolism slows down as you get older. After about age 20, BMR drops a small amount each decade. Our biological age calculator can give you a sense of how your body's age compares to your calendar age.
- Biological sex: Males usually have more muscle and less body fat than females, so their BMR tends to be higher.
BMR vs. TDEE: What's the Difference?
BMR only covers the calories you burn at rest. Your total daily energy expenditure (TDEE) adds in all the calories you burn from walking, exercising, and daily tasks. To find your TDEE, you multiply your BMR by an activity factor. This calculator does that math for you across six activity levels, from sedentary to extra active. If you want to see exactly how many calories specific activities burn, check out our calories burned calculator or walking calorie calculator.
Which BMR Formula Should You Use?
This calculator offers three well-known formulas. The Mifflin-St Jeor equation is the most accurate for most people and is recommended by the Academy of Nutrition and Dietetics. The Revised Harris-Benedict equation is an older formula that is still widely used. The Katch-McArdle formula is best for people who know their body fat percentage, especially lean or athletic individuals, because it uses lean body mass instead of total weight. You can also compare your results with our RMR calculator, which estimates your resting metabolic rate using a similar approach.
Why Knowing Your BMR Matters
Knowing your BMR helps you set smart calorie goals. If you want to lose weight, you need to eat fewer calories than your TDEE — our calorie deficit calculator and weight loss calculator can help you plan that. If you want to gain weight or build muscle, you need to eat more — see our weight gain calculator for guidance. Without knowing your BMR, you are just guessing. Once you have your calorie target, use our macro calculator to split those calories into the right amounts of protein, carbs, and fat, or our calorie calculator for a broader daily calorie estimate. This calculator gives you a solid starting point based on proven science.