BMR Calculator
Estimate basal metabolic rate — calories burned at complete rest.
About the BMR Calculator
This BMR (Basal Metabolic Rate) calculator estimates the number of calories your body burns at complete rest, just to keep you alive — powering your heart, lungs, brain, liver, kidneys, and other organs, and maintaining body temperature. Enter your weight, height, age, and gender, and the tool returns your BMR using the Mifflin-St Jeor equation, the most accurate formula for estimating resting energy expenditure in healthy adults.
BMR is the foundation of any calorie-based nutrition or weight-management plan. It represents roughly 60-75% of total daily energy expenditure for sedentary adults, with physical activity making up most of the remainder (the thermic effect of food accounts for about 10%). Knowing your BMR is essential for setting calorie targets: to lose weight, you need to consume below BMR + activity; to gain weight, above it.
The Mifflin-St Jeor equation, published in 1990, is the formula recommended by the American Dietetic Association (now the Academy of Nutrition and Dietetics) for estimating BMR in healthy adults. It improved on the older Harris-Benedict (1919) and Harris-Benedict Revised (1984) formulas by more accurately predicting measured energy expenditure in modern populations.
How It Works
The Mifflin-St Jeor equation:
Men: BMR = 10 * weight(kg) + 6.25 * height(cm) - 5 * age + 5; Women: BMR = 10 * weight(kg) + 6.25 * height(cm) - 5 * age - 161The formula was derived from regression analysis of 498 healthy adults whose energy expenditure was measured by indirect calorimetry. The coefficients reflect the dominant factors influencing metabolic rate: lean body mass (proxied by weight and height, since muscle is metabolically active tissue), age (metabolic rate declines about 1-2% per decade after age 30, primarily due to muscle loss), and gender (women carry more essential fat and less metabolically active muscle than men at the same weight, resulting in ~5-10% lower BMR).
Each unit of weight contributes 10 kcal/day (the dominant factor); each cm of height contributes 6.25 kcal/day; each year of age subtracts 5 kcal/day. The gender constant is +5 for men and -161 for women.
This calculator returns BMR in kcal/day, the standard unit. For kilojoules, multiply by 4.184.
Worked Examples
Suppose you are a 30-year-old male, 70 kg, 175 cm.
- BMR = 10 * 70 + 6.25 * 175 - 5 * 30 + 5
- = 700 + 1093.75 - 150 + 5
- = 1,648.75 kcal/day ≈ 1,649 kcal/day
For a 30-year-old female, 60 kg, 165 cm:
- BMR = 10 * 60 + 6.25 * 165 - 5 * 30 - 161
- = 600 + 1031.25 - 150 - 161
- = 1,320.25 kcal/day ≈ 1,320 kcal/day
At age 60 (same male, 70 kg, 175 cm): BMR drops to 1,499 kcal/day — about 150 kcal/day less, reflecting age-related metabolic decline. Adding 5 kg of muscle (without changing height or age) raises BMR by 50 kcal/day, illustrating the metabolic benefit of strength training.
When to Use This Tool
Use this BMR calculator when:
- Setting a calorie baseline before designing a weight-loss or weight-gain plan
- Estimating daily calorie needs at complete rest (bedridden patients, hospital stays)
- Calculating the calorie deficit needed to lose a specific amount of weight by a target date
- Comparing your BMR to population averages (about 1,600-1,800 for men, 1,400-1,600 for women)
- Demonstrating the metabolic impact of aging or muscle gain/loss
- Calibrating a fitness tracker or nutrition app that requires a BMR input
- Educational use in nutrition or kinesiology classes
To get your total daily calorie needs, multiply BMR by an activity factor using our TDEE Calculator, or use the Calorie Calculator for a goal-oriented target.
Limitations & Disclaimer
This calculator uses the Mifflin-St Jeor (1990) equation, which has a standard error of approximately 10% in healthy adults. It does not account for body composition (lean vs fat mass, which have different metabolic rates), genetics, hormonal conditions (hypothyroidism, hyperthyroidism, PCOS), medications (SSRIs, beta-blockers, corticosteroids), pregnancy, lactation, recent exercise, ambient temperature, or sleep quality. The formula is calibrated for adults aged 19-78 and BMI 18-50; it may be less accurate for athletes, the elderly, children, or those with significant muscle loss. This is an educational estimate, not a substitute for indirect calorimetry or professional nutritional counseling. See our disclaimer for full terms.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the calories burned at complete rest, just to keep you alive. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor (1.2 for sedentary, 1.9 for very active) to account for daily movement and exercise. TDEE is what you actually burn in a day; BMR is the floor.
Why does the Mifflin-St Jeor formula give a lower number than Harris-Benedict?
The original 1919 Harris-Benedict equation was derived from a small, lean population and tends to overestimate BMR in modern, more sedentary populations by 5-10%. The Mifflin-St Jeor (1990) formula was derived from a more representative sample and is recommended by the Academy of Nutrition and Dietetics for healthy adults.
How accurate is the Mifflin-St Jeor formula?
For healthy adults, the standard error is about 10% (so a 1,500 kcal estimate may be 1,350-1,650 kcal actual). For obese individuals, the formula overestimates by about 5%; for underweight individuals, it may underestimate. For the most accurate BMR, get an indirect calorimetry test at a clinic or sports lab.
Does BMR change as I lose weight?
Yes — BMR drops as you lose weight (less mass to maintain) and as you age. A 70 kg adult who loses 10 kg can expect BMR to drop by about 100 kcal/day. This is why weight-loss plateaus occur: the calorie deficit that produced initial losses is no longer a deficit at the lower BMR. Recalculate BMR after significant weight changes.
How can I increase my BMR?
BMR is largely genetically determined, but you can raise it modestly by: (1) building muscle mass through resistance training (each kg of muscle burns about 13 kcal/day at rest, vs 4 kcal/kg for fat), (2) avoiding crash diets that trigger metabolic adaptation, (3) getting adequate sleep (sleep deprivation lowers BMR by 5-10%), and (4) staying hydrated. Aging, unfortunately, reduces BMR by 1-2% per decade after age 30.
Is BMR the same as RMR?
Not quite. BMR (Basal Metabolic Rate) is measured under strict laboratory conditions: complete rest, after 8+ hours of sleep, 12+ hours of fasting, in a thermoneutral environment. RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 5-10% higher than BMR due to recent activity, digestion, and ambient temperature effects. The Mifflin-St Jeor formula technically estimates RMR but is commonly called BMR in popular usage.
Last updated: July 21, 2026 · Author: HT99 Tools Editorial Team · Reviewed by: HT99 Tools Editorial Team