Mifflin-St Jeor · Harris-Benedict · Katch-McArdle

BMR Calculator

Estimate your Basal Metabolic Rate — the energy your body expends at complete rest — and see your Total Daily Energy Expenditure (TDEE) across all activity levels.

📋 Modify the values and click the Calculate button to use

Age

yrs

Gender

♂ Male♀ Female

Height

Weight

lbs

Exercise: 15–30 min of elevated heart rate activity.
Intense exercise: 45–120 min of elevated heart rate activity.
Very intense exercise: 2+ hours of elevated heart rate activity.

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Enter your details and click
Calculate BMR to see your results.

~70%

of daily energy burn
is from BMR

~20%

from physical
activity

~10%

from food
thermogenesis

26%

unexplained BMR
variance between people

Tip: For Katch-McArdle accuracy, enter your body fat % in Settings above. This formula accounts for lean body mass, making it more precise for athletes and leaner individuals.

Metabolic Science

What Is Basal Metabolic Rate?

BMR is the amount of energy your body needs to maintain vital functions while completely at rest — the baseline that all energy expenditure calculations build upon.

BMR Explained

The basal metabolic rate is measured under very restrictive conditions: the person must be awake but completely rested, with the sympathetic nervous system inactive. It is equivalent to calculating how much fuel a car consumes while idling — no driving, just keeping the engine running.

In this state, energy is used exclusively to maintain vital organs: the heart, brain, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin. For most people, BMR accounts for approximately 70% of total daily energy expenditure. Physical activity contributes ~20%, and food digestion (thermogenesis) ~10%.

Basal metabolism is typically the single largest component of a person's daily caloric need. TDEE = BMR × activity factor (1.2–1.9).

BMR vs. RMR

Though often used interchangeably, BMR and Resting Metabolic Rate (RMR) are technically distinct. BMR requires total physiological equilibrium — a state rarely achieved outside a clinical setting. RMR is measured under more relaxed conditions and is typically 10–20% higher than true BMR.

In practice, most online calculators — including this one — estimate RMR using BMR equations, since true BMR measurement requires specialist equipment (indirect calorimetry). For clinical accuracy, consult a certified specialist or use a handheld calorimetry device available at many health clubs and weight-loss clinics.

⚠ Important: All BMR calculations are estimates. A 2005 meta-analysis found a 26% unexplained variance in BMR between individuals even after controlling for all known factors. Use BMR as a starting framework, not a precise target.

Science-Based Formulas

BMR Estimation Equations

Three validated equations are used by this calculator. Mifflin-St Jeor is the current gold standard for most adults; Katch-McArdle is preferred for leaner individuals who know their body fat percentage.

Mifflin-St Jeor

Current gold standard · Introduced 1990

♂ For Men

BMR = 10W + 6.25H − 5A + 5

♀ For Women

BMR = 10W + 6.25H − 5A − 161

W = weight in kgH = height in cmA = age in years

Revised Harris-Benedict

Classic equation · Revised 1984

♂ For Men

BMR = 13.397W + 4.799H − 5.677A + 88.362

♀ For Women

BMR = 9.247W + 3.098H − 4.330A + 447.593

W = weight in kgH = height in cmA = age in years

Katch-McArdle Formula

Best for lean individuals · Requires body fat %

♂ & ♀ (gender-neutral RDEE)

BMR = 370 + 21.6 × (1 − F) × W

W = weight in kgF = body fat as decimal (e.g. 0.20)

Calculates RDEE (Resting Daily Energy Expenditure), which accounts for lean body mass — making it more accurate for athletes and leaner individuals.

📌 Activity Multipliers (TDEE = BMR × factor)

Sedentary (×1.2) · Light exercise 1–3×/week (×1.375) · Moderate exercise 4–5×/week (×1.465) · Daily exercise / intense 3–4×/week (×1.55) · Intense 6–7×/week (×1.725) · Very intense daily / physical job (×1.9). These multipliers are applied to your BMR to estimate total daily calorie requirements.

Influencing Factors

What Affects Your BMR?

BMR is not a fixed number — multiple biological and environmental factors influence how many calories your body burns at rest.

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Muscle Mass

Aerobic exercise (running, cycling) has little direct effect on BMR. Anaerobic exercise (weightlifting) builds muscle mass, which increases resting energy consumption. More muscle = higher BMR.

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Age

BMR typically decreases with age due to loss of muscle mass (sarcopenia) and hormonal changes. Older adults generally require fewer calories at rest to sustain vital organ function.

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Genetics

Hereditary traits inherited from ancestors influence BMR. Twin studies suggest genetics account for a significant portion of BMR variation that cannot be explained by body composition alone.

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Weather & Temperature

Cold environments raise BMR as the body works to maintain core temperature. BMR increases approximately 7% for every 1.36°F rise in internal body temperature. Fever significantly elevates metabolic rate.

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Diet & Eating Patterns

Small, regularly spaced meals can slightly increase BMR through sustained thermogenesis. Conversely, prolonged starvation or severe calorie restriction can reduce BMR by up to 30% as the body enters an energy-conservation mode.

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Pregnancy & Hormones

Pregnancy raises BMR to support fetal development, which is why calorie needs increase during pregnancy. Menopause and other hormonal changes can increase or decrease BMR depending on their effect on body composition.

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Supplements & Stimulants

Certain compounds raise BMR — most notably caffeine, which is widely used in weight-loss supplements. Thyroid hormones also directly regulate metabolic rate; hypothyroidism lowers BMR, hyperthyroidism raises it.

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Health & Medical Status

Illness (particularly fever), recovery from surgery, and certain medications can temporarily or permanently alter BMR. Body composition changes from disease — such as muscle wasting — also affect baseline energy expenditure.

⚖️

Body Composition

Lean body mass (muscle, bone, organs) is metabolically more active than fat tissue. Two people of identical weight and height may have very different BMRs depending on their muscle-to-fat ratio — hence the Katch-McArdle formula's utility.

Research Insights

BMR Tests & Modern Understanding

What science currently tells us about the accuracy and limitations of BMR estimation.

Limitations of Online BMR Tests

Online BMR calculators — including this one — use statistical equations derived from population data. They provide useful estimates, but cannot account for every individual variation. For the most accurate BMR measurement, indirect calorimetry (measuring oxygen consumption and CO₂ production) is the gold standard.

Handheld calorimetry devices are available at many health clubs, doctor's offices, and weight-loss clinics. If you are making significant medical or nutritional decisions based on BMR, consulting a certified dietitian or sports scientist is strongly recommended.

Using BMR Practically

A calculated BMR and TDEE are starting estimates. Because of individual variation, the actual results from following a BMR-derived calorie target may differ from expectations. The most effective approach is to treat your calculated TDEE as a starting point and then track actual outcomes over several weeks.

Maintaining a daily journal of food intake, exercise, and body weight measurements over longer periods (weekly averages rather than daily) is generally more informative than relying on any single calculation. Adjust targets based on observed trends rather than the numbers alone.

Reference: Johnstone AM, Murison SD, Duncan JS, Rance KA, Speakman JR. "Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine but not sex, circulating leptin, or triiodothyronine." Am J Clin Nutr 2005; 82: 941–948. This meta-analysis demonstrated a 26% unexplained inter-individual variance in BMR when all known factors were controlled.