BMR Calculator

What is BMR?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at rest, in a fasted state, and at a neutral temperature. It reflects the energy needed for basic functions like breathing, circulation, and cell repair.

BMR is the foundation for calculating your daily calorie needs. It does not include calories burned from physical activity or digestion.

What Affects BMR?

  • Muscle mass: More muscle increases BMR because muscle tissue burns more calories than fat, even at rest.
  • Age: BMR generally decreases with age due to loss of muscle mass and hormonal changes.
  • Genetics: Some people naturally have a faster or slower metabolism due to inherited traits.
  • Weather: Exposure to cold can increase BMR as the body works harder to maintain its temperature.
  • Pregnancy: BMR rises during pregnancy to support the growth and development of the fetus.
  • Medications: Certain drugs (such as thyroid medications or stimulants) can raise or lower BMR.
  • Health conditions: Illnesses, hormonal disorders (like hypothyroidism or hyperthyroidism), and other medical conditions can significantly affect BMR.

BMR Calculation Formulas

Mifflin-St Jeor Equation

Most modern and widely used formula for estimating BMR.
Men: 10 × weight (kg) + 6.25 × height (cm) – 5 × age (y) + 5
Women: 10 × weight (kg) + 6.25 × height (cm) – 5 × age (y) – 161

Revised Harris-Benedict Equation

Classic formula, revised for improved accuracy.
Men: (13.397 × weight (kg) + 4.799 × height (cm) – 5.677 × age (y)) + 88.362
Women: (9.247 × weight (kg) + 3.098 × height (cm) – 4.330 × age (y)) + 447.593

Katch-McArdle Equation

Uses lean body mass for a more personalized BMR, recommended if you know your body fat %.
BMR = 370 + (21.6 × LBM)
LBM (Lean Body Mass) = weight × (1 – body fat % / 100)

Limitations of BMR Calculators

  • BMR formulas provide estimates based on population averages and may not reflect individual metabolic differences.
  • They do not account for variations in muscle mass, genetics, hormone levels, or medical conditions.
  • BMR does not include calories burned from digestion (thermic effect of food) or physical activity.
  • Results may be less accurate for athletes, older adults, pregnant individuals, or those with atypical body compositions.
  • Actual calorie needs can be influenced by stress, illness, medications, and environmental factors.

FAQ

BMR estimates are based on population averages and formulas. Individual metabolism may vary due to genetics, muscle mass, and health conditions.

You should recalculate your BMR when your weight, age, or activity level changes significantly.

BMR is measured under stricter conditions (fasted, at rest, neutral temperature), while RMR (Resting Metabolic Rate) is measured under less strict conditions and is usually slightly higher.

References

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