BMR Calculator

Find your Basal Metabolic Rate — the number of calories your body burns at complete rest just to keep you alive.

Unit System

years
Gender
cm
kg

What Is Basal Metabolic Rate?

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to sustain essential biological functions — breathing, blood circulation, cell repair, hormone production, and maintaining core body temperature. It represents the absolute minimum energy your body requires for survival, measured under strict laboratory conditions: lying still, fully rested, in a thermoneutral environment, at least 12 hours after eating.

For most sedentary individuals, BMR accounts for 60±75% of total daily calorie expenditure. It is largely determined by body size, lean muscle mass, age, and biological sex. Understanding your BMR is the essential starting point for setting any meaningful calorie target — whether for fat loss, muscle gain, or maintenance.

How Your BMR Is Calculated

This calculator uses the Mifflin-St Jeor equation, currently considered the most accurate prediction formula for BMR in adults. Developed in 1990 and validated across diverse populations, it consistently outperforms the older Harris-Benedict equation — particularly in individuals with overweight or obesity.

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

For example: a 25-year-old male weighing 70 kg at 175 cm has a BMR of (10 × 70) + (6.25 × 175) - (5 × 25) + 5 = 1,674 kcal/day.

The formula predicts BMR with a typical accuracy of ±10%, which is the best achievable with a population-level prediction model. Actual BMR can only be measured precisely via indirect calorimetry in a clinical setting.

BMR vs TDEE: A Critical Distinction

BMR and TDEE (Total Daily Energy Expenditure) are frequently confused, but they represent very different things:

  • BMR is what your body burns at complete rest — if you did absolutely nothing all day. You should never eat below your BMR for any sustained period, as doing so deprives your body of the energy required for vital functions.
  • TDEE is your actual daily calorie burn, accounting for all physical activity, exercise, and the energy used to digest food. TDEE is always higher than BMR — typically by 20±60% depending on activity level.

If you want to use your BMR to set a weight-loss or muscle-gain calorie target, you need to first calculate your TDEE by multiplying your BMR by an activity factor. Use our TDEE Calculator to do this in one step — it applies the same Mifflin-St Jeor formula with five activity multipliers to give you your complete maintenance calorie needs.

Factors That Affect Your BMR

Several key factors determine your individual BMR:

  • Body size and composition: Larger bodies burn more calories at rest. Each kilogram of lean muscle tissue burns approximately 13 kcal/day at rest, compared to around 4 kcal/kg for fat tissue. This is why building muscle is one of the most effective long-term strategies for raising your BMR.
  • Age: BMR declines by roughly 1±2% per decade after age 20, largely due to the gradual loss of lean muscle mass (sarcopenia) and hormonal changes that accompany ageing.
  • Sex: Men generally have a higher BMR than women of the same height and weight due to greater average lean muscle mass. The Mifflin-St Jeor equation accounts for this with the +5 (male) versus -161 (female) constant.
  • Hormones: Thyroid hormones are the primary metabolic regulators. Hypothyroidism reduces BMR significantly, while hyperthyroidism raises it. Cortisol, insulin, and growth hormone also influence resting metabolic rate.

To maintain or build muscle mass — and protect your BMR as you age — ensure adequate daily protein intake. Use our Protein Calculator to find your personalised protein target, and monitor your overall body composition with our BMI Calculator.

Scientific References: Mifflin MD, et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 51(2):241–247. — Henry CJ. (2005). Basal metabolic rate studies in humans: measurement and development of new equations. Public Health Nutr. 8(7A):1133–1152.

Medical Disclaimer: The results provided by this calculator are for informational and educational purposes only. They are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider or registered dietitian before making significant changes to your diet or exercise plan.

Last reviewed: July 2026 · Based on current WHO & ACSM guidelines.

Frequently Asked Questions

What is a good BMR?

There is no single "good" BMR — it is determined by your body size, age, sex, and muscle mass rather than lifestyle choices. As a rough reference, a BMR below 1,200 kcal is considered below average and may indicate very small body size or significant muscle loss. Between 1,200–2,000 kcal is typical for most adults, and above 2,000 kcal indicates a larger body or above-average muscle mass.

Can I increase my BMR?

Yes — the most effective way to raise BMR is to increase lean muscle mass through resistance training. Muscle tissue is metabolically more active than fat, so each kilogram of muscle you gain slightly raises your resting calorie burn. Eating adequate protein supports muscle retention and growth. Crash dieting, in contrast, lowers BMR by causing muscle loss and metabolic adaptation.

Should I eat below my BMR to lose weight?

No — eating consistently below your BMR deprives your body of the energy needed for essential functions. This leads to muscle loss, hormonal disruption, fatigue, nutrient deficiencies, and a lowered metabolic rate. The correct approach is to eat below your TDEE (not your BMR) by a moderate 250–500 kcal deficit, which creates sustainable fat loss without damaging your metabolism.

How does muscle mass affect BMR?

Lean muscle is more metabolically active than fat tissue at rest. Each kilogram of muscle burns roughly 13 kcal/day, versus about 4 kcal/kg for fat. A person with higher lean mass therefore has a higher BMR than a person of the same total weight but with more body fat. This is why strength training is one of the most effective long-term strategies for increasing resting calorie expenditure.

Does BMR change when you lose weight?

Yes — as you lose weight, your BMR decreases because your body has less mass to maintain. This is one reason fat loss slows down over time and why recalculating your BMR and TDEE every 4–8 weeks is important. Additionally, sustained calorie restriction can cause "adaptive thermogenesis" — a further reduction in BMR beyond what weight loss alone would predict. This is why longer diet breaks are often recommended during extended cuts.

What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is measured under strict conditions: complete physical rest, a thermoneutral environment, and a post-absorptive (fasted) state after at least 12 hours without food. RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10±20% higher than BMR because it includes the energy cost of recent food digestion. In practice, most calculators — including this one — predict RMR while labelling it as BMR, since true BMR conditions are rarely replicated outside a laboratory.