Health
BMR Calculator
Last updated: June 19, 2026
A Basal Metabolic Rate (BMR) calculator is a physical assessment tool that estimates the daily energy expenditure required to sustain basic physiological functions while at complete rest. The calculation employs standard formulas, such as the Mifflin-St Jeor equation, relying on physical attributes including height, weight, biological sex, and age. The resulting output represents the baseline caloric requirement before accounting for physical activity. Fitness planners and individuals use it as a foundational value to determine total energy needs.
Enter your sex, age, height, and weight. We compute your Basal Metabolic Rate using the Mifflin–St Jeor equation, then show what that BMR would mean across the standard activity multipliers.
Quick Answer
Estimate your Basal Metabolic Rate, which is the baseline number of calories your body burns at complete rest. Enter your age, biological sex, height, and weight to see the result.
Sex
Units
BMR is the energy your body would use over 24 hours lying still and not digesting food — your metabolic baseline. To estimate the calories you actually burn in a day, multiply BMR by an activity factor.
For that figure, use the TDEE calculator.
BMR (Mifflin–St Jeor)
1,783 kcal/day
Men · 30y · 82 kg · 178 cm
Estimate, not medical advice. Real BMR varies with body composition, hormones, and health — Mifflin–St Jeor predicts within roughly ±10% for healthy adults.
Examples
30y man, 5′10″, 180 lb
BMR ≈ 1,783 kcal/day
30y woman, 5′6″, 140 lb
BMR ≈ 1,372 kcal/day
45y man, 5′10″, 200 lb
BMR ≈ 1,798 kcal/day
25y woman, 165 cm, 60 kg
BMR ≈ 1,345 kcal/day
How it works
What is BMR?
BMR (Basal Metabolic Rate) is the minimum number of calories your body burns at complete rest just to keep you alive. It powers your heart, lungs, brain, organ function, cell repair, and body temperature — all the involuntary processes that happen without you doing anything.
BMR is typically 60-75% of your total daily calorie burn. The remaining 25-40% comes from physical activity (exercise, walking, fidgeting) and the thermic effect of food (calories burned digesting food).
Your BMR is influenced by age (decreases ~2% per decade after 20), sex (men typically have higher BMR than women at the same weight due to more lean muscle), weight (larger bodies burn more), height (taller bodies burn more), and lean muscle mass (muscle burns more calories at rest than fat).
How the math works
BMR is the calories your body uses over 24 hours at complete rest. Mifflin–St Jeor estimates it from sex, height, weight, and age.
men · 10·kg + 6.25·cm − 5·age + 5
women · 10·kg + 6.25·cm − 5·age − 161
The breakdown also shows what your daily calorie burn would be at each standard activity level (1.2× sedentary through 1.725× very active) — that's the bridge from BMR to TDEE.
BMR vs TDEE — what's the difference?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — just keeping vital functions going. It's the baseline.
TDEE (Total Daily Energy Expenditure) is BMR PLUS all the calories you burn through activity: exercise, walking, daily tasks, even shivering or fidgeting. TDEE is what you actually need to eat to maintain your current weight.
For weight management:
- Eat at TDEE → maintain weight
- Eat below TDEE → lose weight
- Eat above TDEE → gain weight
You can't eat below your BMR safely for extended periods — that's the absolute floor your body needs to function. Very low calorie diets (below BMR) slow metabolism, cause muscle loss, and create rebound weight gain. Use BMR to set a safe minimum, and TDEE to calculate your actual calorie target.
Mifflin-St Jeor vs Harris-Benedict
Two formulas dominate BMR estimation:
MIFFLIN-ST JEOR (1990) — Considered the gold standard. Accurate within ±10% for about 82% of non-obese individuals. Recommended by the American Dietetic Association.
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
HARRIS-BENEDICT (1918, revised 1984) — The original BMR formula. Slightly less accurate than Mifflin-St Jeor (tends to overestimate by ~5% in overweight individuals) but still widely used.
Men: BMR = 88.36 + (13.4 × weight in kg) + (4.8 × height in cm) − (5.7 × age)
Women: BMR = 447.6 + (9.2 × weight in kg) + (3.1 × height in cm) − (4.3 × age)
For most people, use Mifflin-St Jeor. Use Harris-Benedict only when comparing to older research that used it. For very lean athletes who know their body fat percentage, the Katch-McArdle formula is more accurate because it uses lean body mass instead of total weight.
Estimate, not medical advice. Mifflin–St Jeor is accurate to about ±10% for healthy adults; real BMR varies with body composition and health. If you have a medical condition, an eating disorder, are pregnant, or have any nutrition concern, talk to a qualified healthcare professional.
Read the guide: BMR vs TDEE explains the difference between these two numbers and which one to use for weight loss, maintenance, or muscle gain.Related Calculators
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Frequently asked questions
Basal Metabolic Rate is the calories your body burns over 24 hours at complete rest — keeping you breathing, circulating blood, regulating temperature, and running basic cell function. It's the metabolic floor before you account for movement, exercise, or digestion.
BMR is the resting baseline. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for movement, exercise, and the thermic effect of food. TDEE is what you'd actually eat to maintain weight; BMR is just the metabolic floor underneath it.
Mifflin–St Jeor — the formula most commonly recommended by registered dietitians. It outperforms the older Harris–Benedict equation in head-to-head accuracy studies. Men: 10·kg + 6.25·cm − 5·age + 5. Women: 10·kg + 6.25·cm − 5·age − 161.
Mifflin–St Jeor predicts BMR within roughly ±10% for healthy adults. Outliers exist — people with very high or very low muscle mass, or with thyroid or other endocrine conditions, can sit further from the prediction. Treat the number as a starting estimate, not a measurement.
On average, men carry more lean mass than women at the same height and weight, and lean tissue is more metabolically active than fat tissue. The Mifflin–St Jeor offset (+5 for men, −161 for women) approximates this difference at the population level. Individual variation is large — the formula is a population estimator.
BMR drops about 2% per decade after age 20. The biggest reason is muscle loss (sarcopenia). Adults lose roughly 3-8% of muscle mass per decade after 30, and muscle burns more calories at rest than fat. Hormonal changes (declining growth hormone, testosterone) also slow metabolism. Strength training is the most effective way to preserve BMR with aging.
Yes, but modestly. Building muscle through strength training is the most effective long-term strategy — each pound of muscle burns about 6 calories/day at rest (vs. 2 calories/day for fat). Other factors: eating enough protein (supports muscle), getting adequate sleep (poor sleep lowers BMR), and avoiding extreme calorie restriction (slows metabolism). High-intensity exercise produces a small temporary BMR boost (EPOC) lasting 12-24 hours.
BMR varies significantly between individuals — even people of identical age, sex, weight, and height can differ by 200-300 calories/day. Factors include genetics, thyroid function, lean muscle mass, recent dieting history (chronic restriction lowers BMR), and overall fitness level. If your measured BMR seems unusually low, consider testing thyroid function with a doctor.
Yes, especially with prolonged restriction. The body adapts to low calorie intake by reducing BMR — a survival mechanism called metabolic adaptation. After 6+ months of dieting, BMR can drop 100-300 calories below predicted values. This is why aggressive deficits backfire and why diet breaks (returning to maintenance calories periodically) help long-term fat loss.
The Mifflin-St Jeor formula is accurate within ±10% for most people. For a more precise measurement, indirect calorimetry (a metabolic test at a sports medicine clinic) measures actual BMR by analyzing oxygen and carbon dioxide in your breath. The cost is usually $100-300. For most people, the calculator estimate is close enough for nutrition planning.
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