What is BMR (Basal Metabolic Rate)?

BMR is the number of calories your body burns at complete rest just to maintain vital functions — breathing, circulation, digestion, cell production, and organ function. It accounts for 60–75% of your daily total energy expenditure. Your BMR is determined by age, sex, height, weight, and genetics. It typically decreases with age (about 2–8% per decade after age 30) and is higher in men than women due to greater muscle mass.

What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is measured under strict laboratory conditions: fasted 12+ hours, complete rest, neutral temperature (18–21°C). RMR (Resting Metabolic Rate) is measured in real-world conditions without strict controls and is typically 10–20% higher than BMR. For practical purposes, most calculators (including this one) use the Mifflin-St Jeor equation, which estimates RMR. The difference is negligible for diet and fitness planning — use your calculated value as your minimum daily calorie floor.

How do I use BMR to plan my diet?

BMR is your baseline — never eat below it without medical supervision, as it increases muscle loss and metabolic adaptation. To lose weight, create a deficit from your TDEE (BMR × activity factor), aiming for 300–500 kcal below TDEE for safe 0.5–1 kg/week loss. To maintain weight, eat at your TDEE. To gain muscle, eat 300–500 kcal above TDEE. Always keep daily intake above your BMR to preserve muscle, hormones, and metabolism.

What is TDEE and how does it relate to BMR?

TDEE (Total Daily Energy Expenditure) = BMR × Activity Factor. Your BMR alone is your resting metabolism; TDEE includes the calories burned by daily activity, exercise, and digestion (thermic effect of food). Activity factors range from 1.2 (sedentary) to 1.9 (very active). For example, if your BMR is 1,500 kcal and activity factor is 1.55 (moderately active), your TDEE is 2,325 kcal. This TDEE is your maintenance calorie level.

Does BMR change with age?

Yes. BMR decreases approximately 2–8% per decade after age 30 due to loss of muscle mass (sarcopenia) and changes in hormone levels. A 50-year-old may have a BMR 10–20% lower than at age 25, even at the same weight. This is why older adults often find weight loss harder — their baseline calorie burn is lower. However, resistance training preserves and builds muscle, offsetting some age-related BMR decline. Recalculate your BMR every 5–10 years or after significant life changes.

Why is my BMR different on other calculators?

Different equations produce different results. This calculator uses the Mifflin-St Jeor equation (1990) — the most validated and accurate for average-weight adults. Other equations (Harris-Benedict, Katch-McArdle) are less accurate. Body composition matters: the Mifflin-St Jeor equation uses height, weight, age, and sex but doesn't account for muscle vs. fat percentage. A muscular person has higher BMR than a sedentary person at the same weight. If results seem off, consider consulting a sports nutritionist or using indirect calorimetry for precision.

🔥 Metabolism

BMR Calculator 2026

Calculate your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest. Uses the Mifflin–St Jeor equation 1990, the gold-standard formula validated by the American Dietetic Association. Discover your resting metabolism, TDEE (Total Daily Energy Expenditure), and personalized calorie targets for weight loss, maintenance, or muscle gain.

Units

Biological Sex

The Mifflin–St Jeor formula uses different constants for men and women

Age (years)

Used in BMR formula

Height (cm)

Measure barefoot

Weight (kg)

Your current body weight

Activity Level

Be honest — most people overestimate their activity by one tier

🔬 How BMR is Calculated

Step 1 — The Mifflin–St Jeor Equation (1990)

This calculator uses the Mifflin–St Jeor equation, published in the American Journal of Clinical Nutrition in 1990. It is the most validated and accurate BMR formula for average-weight adults, endorsed by the American Dietetic Association and used by clinical nutritionists worldwide.

For Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
For Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

The equation is more accurate than older models (Harris-Benedict 1919, Katch-McArdle) because it was developed on a modern, diverse population.

Step 2 — What BMR Measures

BMR is the minimum calories your body needs to stay alive at complete rest. This includes: basal functions (breathing, circulation, heartbeat), cell production and repair, kidney and liver function, maintaining body temperature, and hormone production. BMR accounts for 60–75% of your total daily calorie burn. The remaining 25–40% comes from physical activity (NEAT and exercise) and digestion (thermic effect of food, ~10% of calories consumed).

Step 3 — BMR vs. RMR: What's the Difference?

BMR (Basal Metabolic Rate) is measured under strict laboratory conditions: fasted 12+ hours, complete physical rest, controlled temperature (18–21°C), and at least 30 minutes of acclimatization. RMR (Resting Metabolic Rate) is measured in normal conditions without fasting or extreme rest and is typically 10–20% higher than true BMR. For practical dieting purposes, the distinction is negligible — the Mifflin-St Jeor equation estimates RMR, and the small difference doesn't meaningfully affect diet planning.

Step 4 — Calculate TDEE (BMR × Activity Factor)

Your Total Daily Energy Expenditure (TDEE) is your BMR multiplied by your activity factor. This gives the total calories you burn in a typical day. Activity factors range from 1.2 (sedentary, minimal exercise) to 1.9 (very active with intense training). For example: BMR of 1,500 kcal × 1.55 (moderately active) = TDEE of 2,325 kcal. Eating at your TDEE maintains weight; below it causes weight loss; above it causes weight gain.

Step 5 — Why BMR Decreases with Age

After age 30, BMR declines approximately 2–8% per decade due to sarcopenia — gradual loss of muscle mass. Muscle is metabolically expensive; every kilogram of muscle burns ~7 kcal/day at rest. As muscle decreases, BMR decreases. Additionally, hormonal changes (lower growth hormone, testosterone, thyroid function) slow metabolism with age. However, resistance training preserves and builds muscle, offsetting age-related BMR decline. A 60-year-old who strength-trains can maintain nearly the BMR of a 30-year-old sedentary person.

📊 TDEE & Activity Factor Guide

Activity Level	Description	Activity Factor	Example TDEE (BMR 1,500)
🪑 Sedentary	Desk job, no exercise	1.2	1,800 kcal
🚶 Lightly Active	Light exercise 1–3 days/week	1.375	2,063 kcal
🏃 Moderately Active	Moderate exercise 3–5 days/week	1.55	2,325 kcal
🏋️ Very Active	Hard exercise 6–7 days/week	1.725	2,588 kcal
⚡ Extra Active	Very hard exercise + physical job	1.9	2,850 kcal

Sources: Mifflin MD et al. (1990), Am J Clin Nutr 51(2):241–7; American Dietetic Association Guidelines.

🎯 Using BMR for Your Fitness Goals

💚 Weight Loss (Fat Loss)

To lose weight, eat 300–500 kcal below your TDEE for a safe rate of 0.5–1 kg per week. Never go below your BMR — this causes muscle loss, metabolic slowdown, and hormonal disruption. For example: if TDEE is 2,300 kcal and BMR is 1,550 kcal, eat 1,800–2,000 kcal/day (300–500 below TDEE, well above BMR). Combine your calorie deficit with resistance training 2–3 times per week and adequate protein (1.6–2.2 g/kg) to preserve muscle mass during loss.

⚖️ Weight Maintenance

To maintain your current weight, eat approximately at your TDEE. Track your weight for 2–3 weeks — if it stays stable, you've found your maintenance calories. If it drifts up or down, adjust by ±100 kcal/day. Maintenance is underrated: once you reach your goal weight, switching to maintenance mode (rather than continued restriction) helps normalize eating patterns, improve energy, and support long-term sustainability.

💪 Muscle Gain / Body Recomposition

To build muscle, eat 300–500 kcal above your TDEE (or 200–300 if you're concerned about fat gain). Combine this surplus with resistance training 3–4 times per week and adequate protein (1.8–2.2 g/kg). Muscle building requires a calorie surplus because your body needs energy to synthesize new tissue. Even with perfect training, you'll gain some fat in a surplus — this is normal. After 8–12 weeks of surplus, take a 4-week maintenance break to allow your body to stabilize.

Understanding Basal Metabolic Rate: The Science Behind Your Resting Calories

Your Basal Metabolic Rate (BMR) is one of the most important but misunderstood metrics in nutrition and fitness. Unlike popular belief, you're not "just sitting around" when your body burns BMR calories — you're powering your entire life support system. Every second, your heart beats, your lungs breathe, your kidneys filter blood, your digestive system moves food, your cells divide and repair, and your brain thinks. All of this requires energy. BMR is the amount of energy — measured in calories — required to keep these vital functions running 24 hours a day at complete rest.

Why BMR Matters More Than Total Calories

Many people obsess over total calorie intake without understanding the floor underneath: your BMR. Eating below your BMR — even if it creates a huge deficit — is counterproductive because your body cannot function. Below-BMR eating triggers metabolic adaptation: your body downregulates thyroid hormones, increases cortisol (stress hormone), and accelerates muscle loss to reduce energy expenditure. This adaptation makes future weight loss harder and is why people who've done extreme diets often struggle for years afterward. The key to sustainable weight loss is respecting your BMR and creating your deficit from TDEE, not BMR.

The Aging Metabolism: Why BMR Declines with Age

Starting around age 30, BMR declines approximately 2–8% per decade. A 50-year-old might burn 10–20% fewer calories at rest than at age 25, even at the same weight. This decline is primarily due to sarcopenia — progressive loss of muscle mass that occurs naturally with age. Muscle is metabolically expensive: each kilogram of muscle burns roughly 7 kcal/day at rest, while fat burns only 2–3 kcal/kg/day. As you lose muscle, your baseline metabolic rate drops. This is why older adults often find weight loss harder and weight gain easier. However, this is not inevitable: resistance training preserves and builds muscle at any age, substantially offsetting age-related metabolic decline.

How Exercise Affects BMR Long-Term

Contrary to popular fitness marketing, you don't need hours of exercise to "boost your metabolism." Short-term metabolic increases from cardio are minimal. The real metabolic benefit comes from building and maintaining muscle mass through resistance training. Each kilogram of lean muscle tissue adds ~7 kcal/day to your BMR. Someone who builds 5 kg of muscle increases their BMR by ~35 kcal/day — seemingly small, but over a year that's a 1.3 kg reduction in body fat without dieting. Combined with consistent cardio and proper nutrition, this is how sustainable body composition change happens.

BMR and Genetics: Why Some People "Just Have a Faster Metabolism"

Genetic differences in BMR exist, but they're smaller than most people believe. Identical twins (same genetics) have BMR values within ~5% of each other. Fraternal twins and siblings average ~20% variation. In practice, the biggest "genetic" differences in metabolic rate are actually differences in muscle mass, not the metabolic efficiency of that muscle. Someone who gained 10 kg of muscle through genetics or training has a higher BMR, but the calories-per-kg of muscle is roughly constant. Individual metabolism varies ~10–15% around predictions, but the Mifflin-St Jeor equation captures ~90% of the variance.

Frequently Asked Questions

What should I eat to stay above my BMR during weight loss? +

Eat at least your BMR value (calculated above) in calories daily. For example, if your BMR is 1,500 kcal, don't eat below 1,500 kcal. Your actual daily intake should be 300–500 kcal below your TDEE — so 1,800–2,000 kcal in this example (TDEE 2,300). Prioritize protein (1.6–2.2 g/kg), whole grains, vegetables, and healthy fats. This combination keeps you full, preserves muscle, and sustains your metabolism during weight loss.

How often should I recalculate my BMR? +

Recalculate every time your weight changes significantly (±5 kg), every 5 years, or after major life changes (illness, injury, training program). If you lose weight, your BMR decreases because there's less body mass to maintain. That's why people hit weight loss plateaus — their original calorie target gradually becomes maintenance instead of a deficit. Use this calculator as a tool to recalibrate quarterly if you're actively trying to lose weight.

Can I increase my BMR permanently? +

Yes, through muscle building. Each kilogram of muscle you gain increases BMR by ~7 kcal/day (~2,500 kcal/year). Resistance training 3–4 times per week with adequate protein (1.8–2.2 g/kg) is the most reliable way. Dietary habits have minor effects: spicy foods, caffeine, and cold exposure cause tiny temporary increases. Sleep, stress management, and thyroid health also affect BMR but through hormonal pathways, not through "boosting metabolism."

Why does this calculator show different results than other websites? +

Different calculators use different equations. This one uses Mifflin-St Jeor (1990) — the most accurate for average-weight adults. Other websites may use Harris-Benedict (1919, less accurate), Katch-McArdle (requires body fat %, estimates it), or Schofield (older). Results may differ by ±100 kcal/day. If uncertain, calculate with multiple equations and average them. Then track your actual weight and food intake for 3 weeks to validate against reality.

Does BMR differ by gender at the same weight/height/age? +

Yes. The Mifflin-St Jeor equation uses different constants for men and women. Women typically have 5–10% lower BMR than men at identical measurements due to having naturally less muscle mass and more fat tissue (by body composition, not just weight). This accounts for hormonal differences too. Two people of the same weight can have different BMRs based on body composition — a muscular woman and a sedentary man at 70 kg will have different true metabolic rates.

What if I'm very overweight or very fit? Is this calculation still accurate? +

The Mifflin-St Jeor equation is most accurate for average-weight individuals (BMI 18.5–25). For overweight/obese individuals, it may overestimate BMR by 5–10%. For very lean/muscular individuals, it may underestimate BMR by 10–15%. The deviation is usually small enough for practical diet planning. If you're very obese or competitive athlete, consider indirect calorimetry or DEXA body composition analysis for precision.

⚕️

Health note: This calculator provides estimates based on the validated Mifflin–St Jeor equation. Individual metabolism varies 10–15% from predictions due to genetics, body composition, hormones, and health conditions. Results are a starting point — track your actual weight, energy levels, and hunger for 2–3 weeks at your calculated TDEE and adjust ±100 kcal/day if needed. Consult a doctor or registered dietitian before making major dietary changes, especially if you have thyroid dysfunction, metabolic disorders, or other health conditions.