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Calculator Answers

BMR Calculator

Source: Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247 · Source verified July 22, 2026

Blake Boege
Written by Blake Boege · Founder, Calculator Answers

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.

See also: TDEE Calculator, Calorie Deficit Calculator, and Macro Calculator.

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

lb
Height
ft
in

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.

Basal Metabolic Rate

BMR (Mifflin–St Jeor)

1,783 kcal/day

Men · 30y · 82 kg · 178 cm

Per hour74 kcal
Sedentary day (× 1.2)2,139 kcal
Light activity (× 1.375)2,451 kcal
Moderate activity (× 1.55)2,763 kcal
Very active (× 1.725)3,075 kcal

Estimate, not medical advice. Real BMR varies with body composition, hormones, and health — Mifflin–St Jeor predicts within roughly ±10% for healthy adults.

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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

Formula · BMR (male) = 10 × weight kg + 6.25 × height cm − 5 × age + 5; BMR (female) = 10 × weight kg + 6.25 × height cm − 5 × age − 161

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

More tools from Health

TDEE CalculatorEstimate your Total Daily Energy Expenditure from sex, age, height, weight, and activity — with maintenance, cut, and bulk targets.Calorie Deficit CalculatorWork out a daily calorie deficit from your maintenance estimate and intake, or the intake that produces a deficit you choose. Also plans backwards from a target weight by date or weekly rate.Macro CalculatorSplit a daily calorie target into grams of protein, carbs, and fat with goal-based presets — fat loss, maintenance, or muscle gain.BMI CalculatorCompute Body Mass Index from height and weight, with the standard category scale and the healthy weight range for your height.

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.

Yes, and the reason is in the equation itself. Mifflin-St Jeor was published as a predictive equation for resting energy expenditure, which is what RMR measures, so the number this page returns is an RMR estimate. The two terms are not perfect synonyms: a true basal measurement is taken under strict laboratory conditions, fasted and immediately after waking, and comes out a few percent below a resting measurement taken under ordinary conditions. Nothing is being measured here either way. One equation is being applied, it was derived on resting subjects, and it returns one number whichever of the two labels you came looking for.

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.