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Basal Metabolic Rate Calculator (BMR)

Calculate your basal metabolic rate using the Harris-Benedict and Mifflin-St Jeor equations. Find out how many calories you burn at rest.

Sources: Roza & Shizgal (1984) -- Harris-Benedict equation reevaluated · Mifflin-St Jeor et al. (1990) -- Resting energy expenditure

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How to Calculate Your Basal Metabolic Rate

Your basal metabolic rate (BMR) is the minimum energy your body requires to survive at complete rest. It is the "energy cost" of vital functions: keeping your heart beating, breathing, maintaining body temperature, and regenerating cells.

The Formulas Used

This calculator applies two scientifically validated equations:

Harris-Benedict (revised by Roza & Shizgal, 1984):

  • Men: BMR = 88.362 + 13.397 x weight(kg) + 4.799 x height(cm) - 5.677 x age
  • Women: BMR = 447.593 + 9.247 x weight(kg) + 3.098 x height(cm) - 4.330 x age

Mifflin-St Jeor (1990):

  • Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5
  • Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161

How It Works

Enter your sex, age, weight, and height. The calculator applies both formulas and shows the results separately, plus their average. The Mifflin-St Jeor formula is generally considered more accurate for modern populations.

Why Knowing Your BMR Matters

Your BMR is the starting point for calculating total calorie needs. Knowing how many calories you burn at rest allows you to:

  • Plan your diet: never eat below your BMR when dieting
  • Understand safe caloric deficit: the difference between TDEE and BMR is your working margin
  • Track changes: BMR changes with age and weight fluctuations

Factors That Influence Metabolism

BMR is not fixed. It varies with muscle mass (more muscle = more calories burned), age (decreases by 1-2% per decade after age 20), thyroid hormones, and nutritional status. Overly restrictive diets can cause an adaptive reduction in metabolic rate, making weight loss harder over time.

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Frequently Asked Questions

What is basal metabolic rate?▼
Basal metabolic rate (BMR) is the amount of energy your body consumes at absolute rest to maintain vital functions: breathing, blood circulation, brain activity, temperature regulation, and cell regeneration. It accounts for approximately 60-75% of total daily calorie expenditure.
What is the difference between Harris-Benedict and Mifflin-St Jeor?▼
The Harris-Benedict formula dates back to 1919 and was revised by Roza and Shizgal in 1984. The Mifflin-St Jeor (1990) is more recent and generally considered more accurate for modern populations. The difference between the two is typically 5-10%. Mifflin-St Jeor tends to give slightly lower values and is recommended by the Academy of Nutrition and Dietetics.
What factors affect basal metabolic rate?▼
The main factors affecting BMR are: muscle mass (more muscle = higher metabolism), age (decreases with aging), sex (men have higher BMR), genetics, thyroid hormones, body temperature, and nutritional status. Overly restrictive diets can lower BMR through metabolic adaptation.