Resting metabolism
BMR Calculator
Calculate your basal metabolic rate in seconds. The BMR calculator below uses the Mifflin–St Jeor equation, the formula validated for clinical use, to estimate the calories your body burns at complete rest.
Basal Metabolic Rate (BMR) is the calories your body burns at complete rest to keep the heart, brain, lungs, and organs running. For most adults BMR falls between 1,400 and 1,800 kcal/day and accounts for 60 to 70 percent of total daily energy expenditure. The most accurate prediction formula is the Mifflin–St Jeor equation, published in 1990 and validated against indirect calorimetry.
Your daily target
· cal/day
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- BMR · cal/day at rest
- BMI ·
- Lean body mass · kg
Pick your goal
Macros at maintenance
30% protein · 40% carbs · 30% fat
Numbers are estimates. Eat at your target for 2 to 3 weeks, track weight, and adjust by ±100 cal/day if it does not match your real maintenance. See how accurate is TDEE?
Show advanced metrics 12 metrics · 7 formulas · 2D macro selector · life-stage
All metrics
Calculate above to populate the full metric table.
All 7 BMR formulas (side-by-side)
Mifflin–St Jeor · Harris–Benedict (revised) · Katch–McArdle · Cunningham · Average · Simple multiplier · Custom
TDEE across activity levels
See how much your TDEE changes between sedentary and athlete. Highlighted bar is your current selection.
Macros: 2D selector
Goal × carb-split matrix: Cut / Maintain / Bulk × Low / Moderate / High carb.
Life-stage adjustments
Luteal phase · Pregnancy (T1/T2/T3) · Breastfeeding · Perimenopause · PCOS
The Mifflin–St Jeor equation
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161Mifflin, St Jeor, Hill, Scott, Daugherty, and Koh published this equation in the American Journal of Clinical Nutrition (1990, 51:241-7, PMID 2305711). Frankenfield et al. later confirmed it predicts resting energy expenditure within 10 percent for 82 percent of non-obese adults, a higher accuracy rate than any competing formula (J Am Diet Assoc, 2005).
What to do with your BMR number
Your BMR alone tells you nothing about how much to eat. To turn BMR into a useful calorie target, multiply it by an activity factor to get your TDEE, then adjust:
- Sedentary (desk job, no exercise): BMR × 1.2
- Lightly active (1 to 3 workouts per week): BMR × 1.375
- Moderately active (3 to 5 workouts per week): BMR × 1.55
- Very active (6 to 7 workouts per week): BMR × 1.725
- Athlete (twice-daily training, physical job): BMR × 1.9
For a deeper breakdown, see the activity level guide. For the difference between resting and total burn, see BMR vs TDEE.
Mifflin–St Jeor vs Harris–Benedict: why we use Mifflin
Harris and Benedict published the original BMR equation in 1919 using 239 subjects, mostly young, lean, and male. Roza and Shizgal revised it in 1984, but the underlying sample never reflected today's adult population. Harris–Benedict overestimates BMR by 50 to 80 kcal/day in most modern adults and by up to 15 percent in obese individuals. Mifflin–St Jeor outperforms it in every head-to-head validation study published since 2000. See the full breakdown on the Mifflin–St Jeor equation page.
BMR vs RMR: are they the same?
Nearly. Researchers measure RMR (resting metabolic rate) under less strict conditions: no overnight fast required, comfortable room temperature, subject awake. RMR runs 5 to 10 percent higher than true BMR. Outside research settings the terms are interchangeable, and this calculator's output works for both.
What lowers your BMR
- Weight loss, especially loss of lean mass (each pound of muscle lost cuts BMR by roughly 6 kcal/day)
- Aging, about 2 percent per decade after age 30, driven mostly by gradual muscle loss
- Chronic under-eating, which triggers metabolic adaptation and downregulates thyroid hormone
- Hypothyroidism, which can drop BMR by 10 to 40 percent
- Sedentary lifestyle, through sarcopenia (age-related muscle loss accelerated by inactivity)
What raises your BMR
- Lean muscle mass, which burns roughly 13 kcal per kg per day at rest, three times the rate of fat tissue
- Cold exposure, which activates brown adipose tissue and adds 100 to 250 kcal/day during sustained exposure
- Caffeine and stimulants, which raise metabolism by 3 to 11 percent for several hours
- Hyperthyroidism, which can elevate BMR by 30 to 100 percent
- Pregnancy and lactation, which add 300 to 500 kcal/day to baseline expenditure
Use your BMR for these decisions
The BMR number drives three practical choices. First, it sets your minimum safe intake: eating below BMR for more than a week or two invites metabolic adaptation, hormonal disruption, and muscle loss. Second, it anchors your calorie deficit: subtract a deficit from TDEE, never from BMR. Third, it explains why two same-sized people need different intakes; BMR varies by ±150 kcal/day at identical height, weight, and age.