Calculate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) using the Mifflin-St Jeor equation — the most accurate formula recommended by the American Dietetic Association. Find out exactly how many calories your body burns at rest and at your activity level. Free, instant, no sign-up.
Mifflin-St Jeor equation — most accurate for most adults
Your Basal Metabolic Rate (BMR) is the number of calories your body burns each day just to keep you alive — breathing, pumping blood, maintaining organ function, and regulating temperature — with zero physical activity. It represents 60–75% of your total calorie burn and is the foundation of every evidence-based diet and weight loss plan. The Mifflin-St Jeor equation, introduced in 1990 and validated by the Academy of Nutrition and Dietetics, is the gold standard for estimating BMR in most adults: 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. Multiply your BMR by your activity multiplier to get TDEE (Total Daily Energy Expenditure) — the number of calories you actually need each day.
BMR decreases with age at roughly 1–2% per decade after age 30, which explains why many Americans find it progressively harder to maintain weight as they get older without reducing intake or increasing activity. Muscle mass is the single biggest lever you can control — each pound of muscle burns approximately 6 calories/day at rest vs. 2 calories/day for a pound of fat. This is why strength training is considered as important as cardio for long-term weight management. Research consistently shows the Mifflin-St Jeor equation is within 10% of measured RMR for about 80% of the population — more accurate than the older Harris-Benedict formula that was standard until the 1990s.
Age (decreases ~2%/decade after 30), gender (men average 5–10% higher than women of same size due to more lean mass), height, weight, body composition (muscle vs fat ratio), thyroid function, and genetics. You cannot control most of these — but muscle mass is actionable.
BMR = calories burned in a fully rested, fasted, thermoneutral state. RMR (Resting Metabolic Rate) ≈ BMR + 10% (measured in normal resting conditions). TDEE = RMR × activity factor. Most diet apps use TDEE. This calculator outputs both for complete accuracy.
CDC-endorsed safe deficit: 500–750 cal/day below TDEE = 1–1.5 lbs/week fat loss. Never go below 1,200 cal/day (women) or 1,500 cal/day (men) without medical supervision. Deficits over 1,000 cal/day significantly increase muscle loss and trigger metabolic adaptation.
Build muscle through resistance training (each lb of muscle burns ~6 cal/day at rest). Don't crash diet — severe restriction reduces BMR by up to 15% (adaptive thermogenesis). Stay protein-rich — the thermic effect of protein burns 20–30% of its calories just in digestion, vs 5–10% for carbs.
Basal metabolic rate is the energy your body spends at complete rest simply staying alive — circulation, respiration, cell repair and maintaining temperature. For most people it is 60–70% of total daily energy use, which is why it anchors every calorie target. The Mifflin-St Jeor equation, published in 1990, is the modern standard and is more accurate for contemporary populations than the 1919 Harris-Benedict equation it replaced. Both are regression formulas fitted to measured data, so they estimate a population average for your characteristics; individual metabolic rates vary by roughly 10% either side for reasons the equations cannot see.
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161Mifflin-St Jeor, 1990where:
Assumptions: An estimate for healthy adults. It does not account for body composition directly, so it under-reads for very muscular people and over-reads at high body fat. Thyroid conditions, medication and prolonged dieting all shift real BMR away from the predicted value.
Work through Mifflin-St Jeor term by term, then convert the result into a daily calorie target.
ResultBMR 1,763 calories — maintenance about 2,732 at moderate activity
The same man sedentary (×1.2) needs 2,115 and very active (×1.725) needs 3,040 — activity swings the target by over 900 calories, far more than any plausible error in the BMR estimate itself. Choosing the activity factor honestly matters more than choosing the equation.