BMR Calculator
Basal Metabolic Rate · TDEE
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Used to highlight your TDEE in results
Enter your details to calculate your Basal Metabolic Rate.
BMR (Mifflin-St Jeor)
0
calories / day at complete rest
Formula Comparison
Mifflin-St Jeor Recommended
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Harris-Benedict (revised)
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TDEE by Activity Level
Sedentary
Desk job, minimal movement
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Lightly Active
1-3 days/week exercise
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Moderately Active
3-5 days/week exercise
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Very Active
6-7 days/week hard exercise
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Extra Active
Athlete or physical job
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Weight Goal Calories (Your Activity)
Lose 1 lb/week—
Lose 0.5 lb/week—
Maintain weight—
Gain 0.5 lb/week—
What Is BMR?
A 30-year-old man who is 5'9" and 160 lb has a BMR of about 1,676 calories a day by the Mifflin-St Jeor equation, and a woman with the same stats about 1,510. BMR is what your body burns at complete rest. The calculator shows your BMR by Mifflin-St Jeor and revised Harris-Benedict, then your TDEE at five activity levels.
BMR (Basal Metabolic Rate) is the number of calories your body needs to sustain basic physiological functions at complete rest: breathing, blood circulation, cell repair, temperature regulation, and organ function. It represents 60-75% of total daily calorie expenditure for most sedentary adults.
Understanding your BMR is the foundation of any evidence-based nutrition plan. Whether your goal is fat loss, muscle gain, or maintenance, you need to know how many calories your body requires before accounting for activity. BMR is not the same as TDEE (Total Daily Energy Expenditure): it must be multiplied by an activity factor to reflect actual daily calorie needs.
| Formula | Year | Men | Women | Accuracy |
|---|---|---|---|---|
| Mifflin-St Jeor | 1990 | 10W + 6.25H - 5A + 5 | 10W + 6.25H - 5A - 161 | Best for general population |
| Harris-Benedict | 1919 / rev.1984 | 88.4 + 13.4W + 4.8H - 5.68A | 447.6 + 9.25W + 3.1H - 4.33A | Tends to overestimate ~5% |
| Katch-McArdle | 1975 | 370 + 21.6 × Lean Body Mass (kg) | Best for lean/athletic individuals | |
W = weight (kg), H = height (cm), A = age (years). Katch-McArdle requires body fat % measurement.
BMR vs TDEE
BMR is your baseline at complete rest. TDEE (Total Daily Energy Expenditure) is BMR multiplied by your activity factor. Sedentary: BMR × 1.2. Lightly active: × 1.375. Moderately active: × 1.55. Very active: × 1.725. Extra active: × 1.9. TDEE is what most nutrition plans are built around: eating below TDEE creates a calorie deficit for fat loss.
What Affects BMR
Muscle mass: the biggest controllable factor. Muscle burns ~6 cal/lb/day at rest vs ~2 cal/lb for fat. Age: BMR falls ~1-2% per decade after 20 due to muscle loss. Sex: men typically have 5-10% higher BMR due to greater lean mass. Body size: larger bodies require more energy. Thyroid function: hypo/hyperthyroidism can shift BMR by 15-40%.
Calorie Deficit for Fat Loss
A deficit of 500 calories a day below TDEE is the traditional estimate for about 1 lb of fat loss a week, from the rule that a pound of fat holds about 3,500 calories. It is a rough guide, not a law: as you lose weight your energy needs fall, so real loss slows and settles below what the rule predicts, which is why the calorie deficit calculator shows the slower dynamic-model figures too. A 250 cal/day deficit = 0.5 lb/week. Safe maximum: 1,000 cal/day deficit (2 lb/week). Never eat below BMR for extended periods: this triggers metabolic adaptation, muscle catabolism, hormonal disruption, and micronutrient deficiencies.
Metabolic Adaptation
When calories are chronically restricted, the body adapts: total daily burn can end up about 10 to 15% below what your new weight predicts, mostly from moving less, with a smaller drop in BMR. This is why fat loss stalls despite adherence. Strategies to minimize adaptation: diet breaks (maintenance calories every 4-6 weeks), resistance training to preserve muscle, adequate protein (1.6-2.2g/kg), and avoiding severe restriction (<25% below TDEE).
Worked Example: Three Formulas, One Person
The default profile: a 30-year-old man, 5'9" (175.3 cm) and 160 lb (72.6 kg).
- Mifflin-St Jeor: 10 × 72.6 + 6.25 × 175.3 − 5 × 30 + 5 = 1,676 calories.
- Harris-Benedict (revised 1984): 88.362 + 13.397 × 72.6 + 4.799 × 175.3 − 5.677 × 30 = 1,731 calories.
- Katch-McArdle needs lean mass. At 20% body fat he has 58.1 kg of lean mass, so 370 + 21.6 × 58.1 = 1,624 calories.
| Formula | Man, 5'9", 160 lb, 30 | Woman, 5'9", 160 lb, 30 |
|---|---|---|
| Mifflin-St Jeor | 1,676 | 1,510 |
| Harris-Benedict (revised) | 1,731 | 1,532 |
| Katch-McArdle, 15% body fat | 1,702 | 1,702 (formula ignores sex) |
| Katch-McArdle, 20% body fat | 1,624 | 1,624 (formula ignores sex) |
The formulas land within about 100 calories of each other here. Harris-Benedict usually reads a little higher, which is why Mifflin-St Jeor is the default. Katch-McArdle ignores sex and age and relies only on lean mass, so it is only as good as your body fat estimate. You can get one from the body fat calculator.
BMR by Weight and Age
Mifflin-St Jeor, calories a day at rest. Women at 5'4", men at 5'10".
| Person | Age 25 | Age 45 | Age 65 |
|---|---|---|---|
| Woman, 120 lb | 1,274 | 1,174 | 1,074 |
| Woman, 140 lb | 1,365 | 1,265 | 1,165 |
| Woman, 160 lb | 1,456 | 1,356 | 1,256 |
| Woman, 180 lb | 1,546 | 1,446 | 1,346 |
| Woman, 200 lb | 1,637 | 1,537 | 1,437 |
| Man, 150 lb | 1,672 | 1,572 | 1,472 |
| Man, 170 lb | 1,762 | 1,662 | 1,562 |
| Man, 190 lb | 1,853 | 1,753 | 1,653 |
| Man, 210 lb | 1,944 | 1,844 | 1,744 |
| Man, 230 lb | 2,035 | 1,935 | 1,835 |
Each extra 20 lb adds about 90 calories, and each extra 20 years takes away 100.
BMR, RMR and What Really Changes Them
BMR vs RMR
Strictly, BMR is measured in a lab after an overnight fast, lying still in a warm room. Resting metabolic rate (RMR) is measured under looser conditions and runs slightly higher. Mifflin-St Jeor was built from resting measurements, so in everyday use the two terms mean the same thing.
Age
The formulas subtract calories for every year of age. A 2021 study in Science of more than 6,400 people found that, once body size and lean mass are accounted for, metabolism holds fairly steady from about 20 to 60 and declines by about 0.7% a year after 60. Much of the drop people notice in midlife comes from losing muscle and moving less, which strength training and daily activity can slow.
Do not eat at your BMR
BMR is not a calorie target. Your daily need is your TDEE, which is higher. Use the calorie calculator for maintenance and the calorie deficit calculator for weight loss. Results are estimates; a doctor or registered dietitian can measure or interpret your metabolism if you have a thyroid condition or other health issue.
Method and sources. Mifflin-St Jeor (Mifflin et al., American Journal of Clinical Nutrition, 1990): 10W + 6.25H − 5A + 5 for men, −161 for women. Revised Harris-Benedict: Roza and Shizgal, 1984. Katch-McArdle: 370 + 21.6 × lean body mass in kg. W = kg, H = cm, A = years. Every value above was computed with these equations, the same ones the calculator uses. Accuracy: Frankenfield et al., 2005. Age: Pontzer et al., Science, 2021. Metabolic adaptation: Rosenbaum and Leibel, 2010. Estimates only, not medical advice.
BMR estimates carry a 10-15% individual error margin. Actual metabolic rate varies with body composition, hormones, and genetics. These are estimates: consult a healthcare professional or registered dietitian for personalized guidance.
BMR & TDEE Questions
BMR (Basal Metabolic Rate) is the calories burned at complete rest: if you stayed perfectly still all day with no digestion or movement. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor to account for exercise, daily movement, digestion (thermic effect of food), and non-exercise activity thermogenesis (NEAT). TDEE is typically 20-100% higher than BMR depending on activity level. Most nutrition and calorie goals are based on TDEE, not BMR. Eating at TDEE maintains weight; eating below TDEE creates a deficit for fat loss; eating above TDEE creates a surplus for muscle gain.
The Mifflin-St Jeor equation (1990) is considered the most accurate for the general population. A landmark 2005 study in the Journal of the American Dietetic Association found it predicted resting energy expenditure within 10% in 82% of non-obese adults and 70% of adults with obesity, outperforming Harris-Benedict. The revised Harris-Benedict (1984) tends to overestimate BMR by approximately 5%. The Katch-McArdle formula (which uses lean body mass instead of total weight) is more accurate for athletes and lean individuals but requires knowing body fat percentage. For obese individuals, the Mifflin-St Jeor formula using actual weight is generally more accurate than the others.
Yes, significantly. BMR decreases by approximately 1-2% per decade after age 20, primarily due to sarcopenia (age-related muscle loss). Muscle tissue burns approximately 3 times more calories at rest than fat tissue, so losing muscle directly reduces BMR. Hormonal changes also contribute: testosterone and growth hormone (which support muscle maintenance) decline with age, and thyroid function can change. This is why a 60-year-old eating the same calories as a 30-year-old of identical height and weight may gradually gain fat. The most effective counter-strategy is resistance training to preserve lean mass and keep BMR elevated with age.
Calculate your TDEE (your BMR from above multiplied by your activity factor), then subtract 250-500 calories for fat loss. A 500 cal/day deficit produces approximately 1 lb of fat loss per week. A 250 cal/day deficit = 0.5 lb/week. Most experts recommend not exceeding a 1,000 cal/day deficit (2 lbs/week maximum). Never eat below your BMR for extended periods: this risks muscle loss, hormonal disruption, and metabolic adaptation. Ensure protein intake is 1.6-2.2g per kg of body weight to preserve lean mass during a deficit. Small, sustainable deficits over time produce better long-term results than aggressive restriction.
The most effective long-term strategy is building muscle through progressive resistance training. Each pound of muscle burns approximately 6 calories per day at rest vs 2 calories for fat. Adding 10 lbs of muscle increases BMR by roughly 60 calories/day. Other evidence-backed approaches: adequate protein intake (thermic effect of protein is 20-30% of calories, vs 5-10% for carbs and 0-3% for fat), avoiding prolonged severe calorie restriction that triggers metabolic adaptation, staying adequately hydrated, getting sufficient sleep (sleep deprivation reduces BMR and increases hunger hormones), and avoiding chronic psychological stress (cortisol promotes fat storage and muscle catabolism).
Thermic effect of food (TEF), also called diet-induced thermogenesis, is the energy required to digest, absorb, and metabolize nutrients. It accounts for approximately 8-15% of total daily energy expenditure. TEF varies by macronutrient: protein has the highest TEF at 20-30% (meaning eating 100 calories of protein "costs" 20-30 calories to process), carbohydrates are 5-10%, and dietary fat is 0-3%. This is one reason high-protein diets have a metabolic advantage: more calories are burned in digestion. TEF is higher for whole, minimally processed foods than for ultra-processed foods with the same calorie content. TEF is not a major contributor to TDEE but does support the preference for protein and whole foods in fat loss protocols.
TDEE includes all energy expenditure beyond pure rest. It consists of four components: BMR (60-75% of TDEE), thermic effect of food (TEF, 8-15%), exercise activity thermogenesis (EAT, 15-30% for active people), and non-exercise activity thermogenesis (NEAT). NEAT is often overlooked but very significant, it includes all movement outside of formal exercise: walking, fidgeting, standing, posture maintenance, household tasks. NEAT varies enormously between individuals (200-900 cal/day) and is one of the main reasons two people with the same BMR can have very different TDEEs. Activity level multipliers (1.2-1.9) capture the combined effect of EAT and NEAT in a simplified way.
Metabolic adaptation (also called adaptive thermogenesis) is the body's response to sustained calorie restriction: it reduces BMR and TDEE below what formulas predict. This is an evolutionary survival mechanism. In studies of people keeping off 10% or more of their weight, total daily energy expenditure ran about 10 to 15% below what their new size predicts; most of that came from less daily movement, with a smaller drop in BMR. This is why fat loss often stalls despite strict adherence to a calculated deficit. Strategies to minimize adaptation: don't restrict below 75% of TDEE, implement diet breaks (return to maintenance calories for 1-2 weeks every 4-6 weeks), prioritize resistance training to preserve metabolically active muscle, ensure adequate protein (1.8-2.4g/kg during aggressive deficits), and avoid consecutive weeks of high-intensity training combined with severe restriction.
Formula-based BMR calculators carry an inherent error margin of 10-15% for most individuals. This means if your calculated BMR is 1,800 calories, your actual BMR could be anywhere from approximately 1,530 to 2,070 calories. Sources of variation: body composition (ratio of muscle to fat at the same weight), genetics (individual metabolic efficiency), thyroid function, chronic medication use (some medications significantly affect metabolic rate), gut microbiome, and ambient temperature acclimatization. For the most accurate BMR measurement, indirect calorimetry (measuring oxygen consumption and CO2 production) is the clinical gold standard. DEXA-based lean mass measurements fed into the Katch-McArdle formula improve calculator accuracy significantly for athletes.
Men typically have 5-10% higher BMR than women of the same age, height, and weight. The primary reason is body composition: men tend to have greater lean muscle mass and lower body fat percentage than women at equivalent weights, and muscle is metabolically more active than fat. Hormonal differences also play a role: testosterone promotes muscle protein synthesis and fat oxidation, while higher estrogen levels in women are associated with slightly lower metabolic rates. Pregnancy significantly increases BMR (by 15-20% in the third trimester) due to fetal growth, placental metabolism, and increased cardiac output. Menstrual cycle phase also causes minor BMR fluctuations (typically 2-9% higher in the luteal phase before menstruation). The Mifflin-St Jeor and Harris-Benedict formulas account for these differences through sex-specific constants.
For adults, BMR usually falls between about 1,100 and 1,700 calories a day for women and 1,400 and 2,100 for men, depending on size and age. A 25-year-old woman at 5'4" and 140 lb is about 1,365; a 45-year-old man at 5'10" and 190 lb is about 1,753. There is no single healthy number: a higher BMR mostly reflects a larger or more muscular body.
Almost. BMR is measured under strict lab conditions (overnight fast, lying still, warm room), while resting metabolic rate is measured more loosely and comes out slightly higher. Online formulas like Mifflin-St Jeor were built from resting measurements, so for planning meals you can treat the two as the same number.