Calculate your Basal Metabolic Rate using both Mifflin-St Jeor and Harris-Benedict formulas.
Ages 15–100
Daily calories by activity level (TDEE, Mifflin-St Jeor)
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions or starting any diet or exercise programme.
🔥 What to do with your BMR?
Multiply your BMR by your activity multiplier to get TDEE (your actual daily calorie need). The results table below shows your estimated TDEE at each activity level.
🧠 Mifflin-St Jeor (1990) — Recommended:
Male: BMR = 10W + 6.25H − 5A + 5
Female: BMR = 10W + 6.25H − 5A − 161
🏷️ Harris-Benedict (1919, revised 1984):
Male: 88.362 + 13.397W + 4.799H − 5.677A
Female: 447.593 + 9.247W + 3.098H − 4.330A
W = kg, H = cm, A = years
Did you know?
Your BMR decreases by roughly 1–2% per decade after age 20, largely because we lose muscle mass (sarcopenia) with age. But strength training can reverse this — a 70-year-old who lifts weights can have the muscle mass and BMR of someone 20 years younger.
The science of basal metabolism began with German physiologist Max Rubner in the 1880s. He proposed the "surface law" — that metabolic rate scales with body surface area rather than weight. Wilbur Atwater and Francis Benedict refined this with their human calorimeter experiments at the Nutrition Laboratory in Boston (1899–1910). James Arthur Harris and Francis Gano Benedict published their landmark equations in 1919 using whole-body calorimetry on 239 subjects. In 1984, Roza and Shizgal revised the equations. Then in 1990, Mifflin, St Jeor, and colleagues published their more accurate update in the American Journal of Clinical Nutrition, using a wider, more representative population sample. This equation now forms the basis of nutritional guidance in over 30 countries.
Your brain consumes about 20% of your total BMR — roughly 300–500 cal/day for an organ that weighs just 1.4 kg, making it by far the most metabolically expensive tissue in the body.
BMR is higher in colder climates because the body burns more energy maintaining its 37°C core temperature against the cold environment.
Thyroid hormones (T3 and T4) are the primary regulators of BMR. Hypothyroidism can reduce BMR by up to 40%; hyperthyroidism can increase it by 80% — explaining dramatic weight changes with thyroid disorders.
Fever raises metabolic rate by roughly 10–13% for every 1°C increase in body temperature. During a 40°C fever, your body can burn around 30–40% more calories than normal — which is why illness causes rapid weight loss.
Professional athletes and very muscular individuals have higher BMRs because muscle tissue burns roughly 3× more calories at rest than fat tissue.
Sleep reduces BMR by only about 5–10% — the idea of "not burning calories while sleeping" is largely a myth. Your body is extremely active repairing tissues, consolidating memories, and regulating hormones while you sleep.
The Mifflin-St Jeor equation is generally considered more accurate for modern adults, validated to be within 10% for 82% of the population. The Harris-Benedict equation tends to overestimate by 5% on average in modern populations, possibly because activity levels were higher in the 1919 study cohort.
Primarily due to sarcopenia — the gradual loss of muscle mass that begins around age 30, accelerating after 60. Since muscle is metabolically active tissue, less muscle = lower BMR. Secondary causes include declining hormone levels (testosterone, growth hormone) and reduced organ function.
Yes! The most effective method is resistance training to build and maintain muscle mass. High-protein diets also slightly raise BMR via the thermic effect of food. Staying well hydrated and getting adequate sleep are underrated factors that help maintain BMR. Some supplements claim to raise BMR, but evidence is weak.
Resting Metabolic Rate (RMR) is measured at rest but not under the strict conditions required for true BMR (12-hour fasting, thermoneutral environment, post-sleep). RMR is typically 10–20% higher than BMR because it includes slight digestion and movement. Most online calculators technically calculate RMR but call it BMR.
The Mifflin-St Jeor equation (Men: 10×weight + 6.25×height − 5×age + 5; Women: same but −161) is considered the gold standard for BMR estimation. The older Harris-Benedict equation tends to overestimate BMR by 5–15%, which can lead to slower weight loss if used for calorie planning. This calculator shows both formulas for comparison.