BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest
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Calculate Your BMR
Enter your details to see your Basal Metabolic Rate using two validated formulas.
What is Basal Metabolic Rate?
Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic life functions at complete rest. These functions include breathing, circulating blood, cell production, nutrient processing, and temperature regulation.
If you stayed in bed all day without moving, your BMR is the energy your body would burn. It represents 60-75% of your total daily calorie expenditure, making it the single largest component of your energy needs.
BMR vs. RMR
Resting Metabolic Rate (RMR) is often used interchangeably with BMR but is slightly different. RMR is measured under less strict conditions and tends to be about 10-20% higher than BMR. Most online calculators (including this one) technically estimate RMR but use the term BMR colloquially.
Factors That Affect BMR
- Muscle mass: Muscle tissue burns more calories at rest than fat tissue. More muscle = higher BMR
- Age: BMR decreases approximately 1-2% per decade after age 20, mainly due to loss of lean muscle mass
- Biological sex: Males typically have higher BMR due to greater muscle mass and lower body fat percentage
- Body size: Larger bodies require more energy to maintain basic functions
- Genetics: Metabolic rate has a genetic component; some people naturally burn more calories
- Hormones: Thyroid hormones significantly impact metabolic rate. Hyperthyroidism increases BMR; hypothyroidism decreases it
- Body temperature: Fever increases BMR by about 7% for each degree Fahrenheit above normal
- Climate: People living in very cold or very hot environments may have slightly higher BMR
Comparing BMR Formulas
Mifflin-St Jeor (1990) — Recommended
Developed in 1990 using modern regression analysis on contemporary populations. Multiple validation studies have found it to be the most accurate equation for estimating BMR in healthy, non-obese adults. The American Dietetic Association recommends this formula.
Harris-Benedict (Original 1919, Revised 1984)
Originally developed in 1919 and revised by Roza and Shizgal in 1984. This is the most widely known formula but tends to overestimate BMR by 5-15%, particularly in overweight individuals. It was developed using older methodologies and populations.
Which Should I Use?
For most healthy adults, the Mifflin-St Jeor equation provides the most accurate estimate. The Harris-Benedict result is shown for reference and comparison. If both formulas give you similar results, you can feel more confident in the estimate.
Using Your BMR
Your BMR alone doesn't tell you how many calories to eat — you need to account for physical activity. Multiply your BMR by an activity factor to get your Total Daily Energy Expenditure (TDEE).
The Caloric Floor
Your BMR represents the minimum calories your body needs for basic functions. Consistently eating below your BMR can lead to:
- Metabolic slowdown (adaptive thermogenesis)
- Muscle loss and decreased strength
- Nutrient deficiencies
- Hormonal disruption
- Fatigue and poor concentration
For safe weight loss, eat below your TDEE but above your BMR. Use our TDEE Calculator or Calorie Deficit Calculator for personalized weight loss targets.
Frequently Asked Questions
BMR is the calories burned at complete rest for basic body functions. TDEE is your total daily calorie burn including BMR plus all physical activity, exercise, and the thermic effect of food. TDEE is always higher than BMR and represents your actual calorie needs.
Yes, the most effective way is to build muscle through resistance training. Each pound of muscle burns about 6-7 calories per day at rest, compared to 2-3 calories per pound of fat. Regular exercise, adequate sleep, and proper protein intake all support a healthy metabolic rate.
Men generally have more lean muscle mass and lower body fat percentage than women of the same weight. Since muscle tissue is more metabolically active than fat tissue, this results in a higher BMR. Hormonal differences (higher testosterone in men) also contribute to higher metabolic rates.
Prolonged severe calorie restriction can cause adaptive thermogenesis, where your body reduces its metabolic rate to conserve energy. This is why crash diets often backfire. A moderate calorie deficit (500 calories below TDEE) combined with resistance training minimizes metabolic slowdown.
No. Eating at BMR means you're already in a significant calorie deficit (since you burn more than BMR through daily activity). Most experts recommend eating between BMR and TDEE for weight loss. Women should generally not go below 1,200 calories and men below 1,500 calories without medical supervision.
Online BMR calculators estimate within about 10% of your actual BMR for most people. The gold standard for measuring true BMR is indirect calorimetry (breathing into a metabolic cart). Calculator estimates may be less accurate for very muscular individuals, the elderly, or those with metabolic conditions.
⚠ Disclaimer
BMR calculations are estimates based on statistical equations. Your actual metabolic rate may differ based on body composition, genetics, hormones, and other individual factors. These results should be used as a starting point for dietary planning. Consult a healthcare provider before making significant changes to your diet, especially if you have medical conditions.
References & Sources
- Mifflin MD, St Jeor ST, et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2), 241-247.
- Roza AM, Shizgal HM (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. American Journal of Clinical Nutrition, 40(1), 168-182.
- Frankenfield D, et al. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. Journal of the American Dietetic Association, 105(5), 775-789.
- American Dietetic Association. Position paper on weight management — recommending Mifflin-St Jeor for BMR estimation.
- National Institutes of Health (NIH). Understanding metabolism and body weight. niddk.nih.gov