BMR Calculator

Calculate your Basal Metabolic Rate, the number of calories your body burns at complete rest. Uses the Mifflin-St Jeor formula with Harris-Benedict comparison.

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What Is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns every day at complete rest, just to keep you alive. Think of it as the energy cost of running your internal machinery: heart, lungs, kidneys, brain, and every cell in your body constantly consuming energy even when you're sleeping.

BMR typically accounts for 60–70% of total daily calorie burn for most people. The remaining calories come from physical activity, exercise, and digesting food (thermic effect of food).

The Mifflin-St Jeor Equation

Developed in 1990, the Mifflin-St Jeor equation is the gold standard for BMR estimation. Multiple independent studies have validated it as the most accurate formula for non-athletes, and it's the preferred equation of the Academy of Nutrition and Dietetics.

Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161

The difference between male and female equations (the constant +5 vs −161) reflects the average difference in lean body mass and hormonal factors between biological sexes.

BMR vs TDEE: Which Should You Use?

BMR alone is an incomplete picture. If you want to set a calorie target for weight loss, maintenance, or muscle gain, you need your TDEE (Total Daily Energy Expenditure).

TDEE = BMR × Activity Factor

Activity factors range from 1.2 (sedentary) to 1.9 (extremely active). Our TDEE Calculator does this automatically, enter the same stats and get your full daily calorie burn including activity.

Factors That Affect Your BMR

BMR is not fixed, it changes throughout your life based on several factors:

Age: BMR decreases by approximately 2% per decade after age 20 due to muscle loss
Body composition: More muscle = higher BMR (muscle burns ~3× more calories at rest than fat)
Weight: Heavier people have higher BMRs, more mass requires more energy to sustain
Hormones: Thyroid hormones regulate metabolic rate; imbalances can raise or lower BMR significantly
Diet history: Prolonged severe restriction causes adaptive thermogenesis, the body reduces BMR to conserve energy

How to Boost Your BMR

The most effective evidence-based strategies for raising BMR are:

Build and preserve muscle through resistance training (each kg of muscle adds ~13 kcal/day to BMR)
Avoid extreme calorie restriction that causes muscle loss and metabolic adaptation
Eat enough protein (1.6–2g/kg/day) to maintain muscle during any fat loss phase
Prioritise sleep, sleep deprivation reduces BMR and increases hunger hormones
Stay hydrated, mild dehydration can reduce metabolic rate by up to 3%

Frequently Asked Questions

What is BMR (Basal Metabolic Rate)?

BMR is the number of calories your body burns at complete rest to maintain basic life functions, breathing, circulation, temperature regulation, and cell repair. It represents the minimum energy your body needs to survive without any activity.

What formula does this BMR calculator use?

This calculator uses the Mifflin-St Jeor equation (1990), which is considered the most accurate BMR formula for the general population. We also show the original Harris-Benedict result for comparison. Most registered dietitians and nutrition researchers use Mifflin-St Jeor.

What is the difference between BMR and TDEE?

BMR is your calorie burn at rest. TDEE (Total Daily Energy Expenditure) is your actual total calorie burn including all activity. TDEE = BMR × activity multiplier (1.2 to 1.9). You should always base your calorie targets on TDEE, not BMR alone.

Should I eat at my BMR?

No, eating at your BMR means you would be in a calorie deficit because your BMR doesn't include the calories you burn moving and living. Eating below BMR long-term is generally not recommended as it risks muscle loss and nutrient deficiencies.

Why is my BMR lower than expected?

BMR decreases with age (muscle mass declines), decreases when you lose weight (less body mass to sustain), and is lower in women than men due to hormonal differences and generally lower muscle mass. It can also be lower after extended calorie restriction due to metabolic adaptation.

How does muscle mass affect BMR?

Muscle is metabolically active tissue, it burns more calories at rest than fat. Every kilogram of muscle burns approximately 13 kcal/day at rest vs ~4.5 kcal/kg for fat. This is why strength training helps maintain a higher BMR during weight loss.

How accurate is the Mifflin-St Jeor equation?

The Mifflin-St Jeor formula predicts BMR within 10% for approximately 80% of the population. It can be less accurate for very muscular individuals (underestimates) and very obese individuals (overestimates). For greater accuracy, a metabolic rate test via indirect calorimetry is available at some clinics.

Can I increase my BMR?

Yes, the most effective ways are building muscle through strength training, avoiding prolonged severe calorie restriction that causes muscle loss, getting adequate sleep (poor sleep reduces BMR), and staying well-hydrated. Eating adequate protein is also essential for maintaining muscle mass.

How it's calculated: this tool uses established, published equations. See the full calculator methodology for the formulas and assumptions behind it.

Results are estimates for general guidance, not medical advice. See our disclaimer, and speak to a qualified healthcare professional before making medical or dietary changes.