Basal Metabolic Rate Calculator

Calculate your Basal Metabolic Rate (BMR) to determine the precise number of calories your body needs solely for resting, vital functions.

US Units
Metric Units
ages: 15 - 80

BMR = /day

Activity LevelCalorie
Sedentary: little or no exercise
Exercise 1-3 times/week
Exercise 4-5 times/week
Daily exercise or intense exercise 3-4 times/week
Intense exercise 6-7 times/week
Very intense exercise daily, or physical job
Exercise: 15-30 minutes of elevated heart rate activity.
Intense exercise: 45-120 minutes of elevated heart rate activity.
Very intense exercise: 2+ hours of elevated heart rate activity.

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Calculation Examples

Calculation Case Result
Male, 30 years, 180 cm, 80 kg BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = 800 + 1,125 − 150 + 5 = 1,780 kcal/day
Female, 30 years, 165 cm, 60 kg BMR = (10 × 60) + (6.25 × 165) − (5 × 30) − 161 = 600 + 1,031 − 150 − 161 = 1,320 kcal/day
Male, 50 years, 175 cm, 85 kg (age effect) BMR = (10 × 85) + (6.25 × 175) − (5 × 50) + 5 = 1,756 kcal/day

How to Use the Basal Metabolic Rate Calculator

Enter your age, sex, weight, and height. Select your preferred unit system (metric: kg/cm; imperial: lbs/inches). Click "Calculate" to apply the Mifflin-St Jeor equations: Men: $BMR = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} + 5$; Women: $BMR = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} - 161$. The result is the estimated number of kilocalories your body burns per day at complete rest - your metabolic baseline, independent of any physical activity. To calculate your Total Daily Energy Expenditure (TDEE), multiply this BMR by your Physical Activity Level (PAL) multiplier.Mifflin-St Jeor BMR formula for men and women with variable definitions

Factors That Influence BMR

BMR is determined primarily by lean body mass - the metabolically active tissue in the body. Skeletal muscle is significantly more metabolically expensive at rest than adipose tissue: research by Gallagher et al. (*Am J Physiol.* 1998) estimated resting energy expenditure in muscle at approximately 13 kcal/kg/day, compared to approximately 4.5 kcal/kg/day for fat tissue. This means that two individuals with the same total body weight but different body compositions will have meaningfully different BMRs - the person with more muscle will require more calories at rest.

BMR declines with age, primarily due to the progressive loss of skeletal muscle mass known as sarcopenia. Doherty TJ (*J Appl Physiol.* 2003) reviewed this process and noted that muscle mass declines at roughly 1–2% per decade from age 20, accelerating after age 60 - a key contributor to the age-related reduction in resting metabolic rate. This decline is not inevitable: consistent resistance training is the most effective intervention for preserving muscle mass and maintaining BMR across the lifespan. Additional factors that can temporarily or chronically reduce BMR include prolonged severe calorie restriction (metabolic adaptation), chronic sleep deprivation, and clinically diagnosed hypothyroidism.

BMR energy breakdown: proportion of total daily energy expenditure at different activity levels

Useful Tips 💡

  • BMR is your absolute metabolic floor - the minimum calorie requirement to sustain vital organ function at complete rest. Do not sustain a calorie intake at or below your BMR without medical supervision, as this accelerates muscle loss and triggers metabolic adaptation.
  • Use BMR as the foundation for TDEE calculation rather than as a dietary target on its own. BMR × PAL multiplier = TDEE (maintenance). A safe weight loss target is TDEE minus 500–750 kcal/day, per Academy of Nutrition and Dietetics guidelines.
  • If your weight has changed by more than 3–5 kg since your last calculation, recalculate BMR - the Mifflin-St Jeor formula is directly weight-dependent and a stale BMR figure will make your TDEE and calorie targets increasingly inaccurate over time.

📋Steps to Calculate

  1. Enter your age (years), sex, weight (kg or lbs), and height (cm or inches).

  2. Select your preferred unit system: metric (kg/cm) or imperial (lbs/inches).

  3. Click "Calculate" to view your BMR in kilocalories per day using the Mifflin-St Jeor equation.

Mistakes to Avoid ⚠️

  1. Confusing BMR with TDEE: BMR is the calorie requirement at complete rest (no activity). TDEE includes BMR plus all physical activity. Using BMR as a dietary target without the PAL multiplier systematically underestimates true daily calorie needs.
  2. Using the Harris-Benedict equation (1919) when Mifflin-St Jeor is available. The JADA meta-analysis (2005) found Mifflin-St Jeor predicted measured resting energy expenditure within ±10% for approximately 82% of participants, versus approximately 45% for the revised Harris-Benedict - a material difference in clinical accuracy.
  3. Failing to recalculate BMR after significant weight changes. BMR is weight-dependent, so a result calculated at 90 kg becomes progressively less accurate as weight drops to 80 kg over a diet phase.
  4. Applying a standard BMR formula for athletes with very high muscle-to-fat ratios: the Katch-McArdle formula [BMR = 370 + (21.6 × Lean Body Mass kg)] uses fat-free mass directly and may produce a more accurate estimate for individuals who know their body fat percentage.

Practical Applications📊

  1. Use BMR as your metabolic floor for safe calorie planning - clinical guidelines (NIH, Academy of Nutrition and Dietetics) advise against sustained intake below 1,200 kcal/day for women or 1,500 kcal/day for men, thresholds that often fall near BMR for smaller individuals.

  2. Multiply your BMR by a Physical Activity Level (PAL) factor to calculate TDEE: Sedentary (×1.2), Lightly Active (×1.375), Moderately Active (×1.55), Very Active (×1.725), Extra Active (×1.9). This TDEE is your maintenance calorie level - the starting point for any weight management plan.

  3. Recalculate BMR every 4–6 weeks during active weight loss or muscle gain, since the Mifflin-St Jeor formula is weight-dependent and your BMR changes as body weight changes. A 5 kg reduction typically reduces BMR by approximately 50–100 kcal/day.

Questions and Answers

What is a BMR calculator and why does it matter for nutrition planning?

A Basal Metabolic Rate (BMR) calculator estimates the number of kilocalories your body requires to sustain vital physiological functions - including respiration, cardiac function, thermoregulation, and cellular repair - at complete rest with no digestive activity. BMR is your metabolic floor: the calorie amount below which the body begins to catabolize muscle tissue and downregulate metabolic processes to conserve energy. For sedentary individuals, BMR accounts for approximately 60–70% of total daily energy expenditure; this proportion decreases as physical activity increases.

How is BMR calculated using the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation (Mifflin MD et al., Am J Clin Nutr. 1990;51(2):241-7) is the reference method for estimating resting energy expenditure: Men: $BMR = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} + 5$; Women: $BMR = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} - 161$. For a 35-year-old woman weighing 65 kg and 168 cm tall: BMR = (10×65) + (6.25×168) − (5×35) − 161 = 650 + 1,050 − 175 − 161 = 1,364 kcal/day. The Academy of Nutrition and Dietetics recognizes Mifflin-St Jeor as the preferred equation for estimating resting energy expenditure in clinical practice.

What is the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is the calorie requirement at complete rest - the metabolic cost of maintaining vital functions with zero physical activity. TDEE (Total Daily Energy Expenditure) is BMR multiplied by a Physical Activity Level (PAL) factor that accounts for the energy cost of movement, exercise, and food digestion: $TDEE = BMR \times \text{PAL}$. PAL values range from 1.2 (sedentary, desk work) to 1.9 (twice-daily training or physical labor). TDEE also includes TEF (Thermic Effect of Food) - approximately 10% of total caloric intake - which is incorporated into the PAL multipliers. BMR is the starting point; TDEE is the actionable calorie target for dietary planning.

How does muscle mass affect BMR compared to fat mass?

Skeletal muscle tissue is significantly more metabolically active than adipose tissue at rest. Gallagher et al. (*Am J Physiol.* 1998) estimated resting energy expenditure in skeletal muscle at approximately 13 kcal/kg/day, compared to approximately 4.5 kcal/kg/day for fat tissue. This means that adding 5 kg of muscle mass increases resting calorie burn by approximately 65 kcal/day - not dramatic on a daily scale, but meaningful over months and years. Standard BMR formulas use total body weight and cannot directly account for muscle-to-fat ratio; individuals with above-average muscle mass (athletes, strength trainers) will typically have a higher actual BMR than the formula predicts. For these individuals, the Katch-McArdle formula [BMR = 370 + (21.6 × LBM kg)] - which uses Lean Body Mass directly - may provide a more accurate estimate.

Why does BMR decrease with age, and how can it be slowed?

The age-related decline in BMR is primarily caused by the progressive loss of skeletal muscle mass (sarcopenia). Doherty TJ (*J Appl Physiol.* 2003) noted in his invited review that muscle mass declines at roughly 1–2% per decade from the age of 20, with the rate accelerating after 60. Because muscle is the primary metabolically active tissue driving BMR, less muscle mass means fewer resting calories burned. The most effective intervention to slow this decline is progressive resistance training (weightlifting, bodyweight exercise), which has been consistently shown in clinical literature to preserve lean mass and maintain BMR across the lifespan. Adequate dietary protein intake (1.2–2.2 g/kg bodyweight/day, per ISSN guidelines) supports muscle protein synthesis and further mitigates age-related muscle loss.

Which is more accurate: Mifflin-St Jeor or Harris-Benedict?

A meta-analysis published in the Journal of the American Dietetic Association (2005) compared four BMR prediction equations - Mifflin-St Jeor, Harris-Benedict (revised), Owen, and WHO/FAO/UNU - across a diverse adult population. Mifflin-St Jeor predicted measured resting energy expenditure within ±10% for approximately 82% of participants, compared to approximately 45% for the revised Harris-Benedict equation. The Harris-Benedict equation was developed in 1919 on a sample of 239 primarily healthy, lean young adults and consistently overestimates BMR in contemporary populations, which tend to have higher average body fat percentages and lower activity levels than the original sample. Mifflin-St Jeor, developed in 1990 on a more contemporary and diverse population, corrects for this systematic bias.

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Disclaimer: This calculator is designed to provide helpful estimates for informational purposes. While we strive for accuracy, financial (or medical) results can vary based on local laws and individual circumstances. We recommend consulting with a professional advisor for critical decisions.