BMR Calculator
Free BMR (Basal Metabolic Rate) calculator — uses the Mifflin-St Jeor equation, the formula clinical dietitians prefer, with Harris-Benedict as a comparison. Metric units (kg, cm). Runs in your browser.
Enter your sex, weight, height, and age. The calculator returns your basal metabolic rate (BMR) — how many calories your body burns at complete rest — using the Mifflin-St Jeor equation, the standard in modern clinical practice. Harris-Benedict is shown for comparison.
What BMR means
BMR is the energy your body consumes just to stay alive: heartbeat, brain function, breathing, body temperature. It’s the biggest slice of your daily calorie burn — roughly 60–70% for most people. The rest comes from movement, digestion, and exercise; add those up and you get your TDEE (total daily energy expenditure).
Mifflin-St Jeor formula
The calculator uses the Mifflin-St Jeor equation (Am J Clin Nutr, 1990), which most clinical dietitians prefer over the older Harris-Benedict formula:
Male: BMR = 10·W + 6.25·H − 5·A + 5 Female: BMR = 10·W + 6.25·H − 5·A − 161
W = weight in kg, H = height in cm, A = age in years.
Harris-Benedict (revised 1984) is shown as a comparison so you can see the spread between the two most common formulas. Mifflin-St Jeor is the one to use for practical planning.
Worked example
A 30-year-old man, 80 kg, 180 cm:
BMR = 10·80 + 6.25·180 − 5·30 + 5 = 1,780 kcal/day (Mifflin-St Jeor). Harris-Benedict gives 1,854 kcal/day, about 4% higher.
A 30-year-old woman, 65 kg, 165 cm:
BMR = 10·65 + 6.25·165 − 5·30 − 161 = 1,370 kcal/day (Mifflin-St Jeor). Harris-Benedict gives 1,430 kcal/day, about 4% higher.
From BMR to TDEE
If you need to know how many calories you actually burn in a day (accounting for exercise, walking, and daily activity), multiply BMR by an activity factor — that’s your TDEE. Use the TDEE calculator to factor in your activity level and get your full calorie target.
Worked examples
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Male, 80 kg, 180 cm, 30 years
BMR: 1,780 kcal/day (Mifflin-St Jeor) — Harris-Benedict estimates 1,854 kcal/day.
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Female, 65 kg, 165 cm, 30 years
BMR: 1,370 kcal/day (Mifflin-St Jeor) — Harris-Benedict estimates 1,430 kcal/day.
Frequently asked questions
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — just to keep your heart beating, lungs breathing, brain running, and body warm. It accounts for roughly 60–70% of the calories you burn in a day. Everything else (walking, digesting, exercise, even fidgeting) stacks on top of BMR to make your TDEE (Total Daily Energy Expenditure).
What's the difference between BMR and TDEE?
BMR is calories at absolute rest. TDEE is BMR multiplied by an activity factor (sedentary ×1.2 up to very active ×1.9). If you're trying to lose weight, eat below your TDEE — not below your BMR. Eating below BMR for long periods can slow metabolism and cost lean mass. Use our [TDEE calculator](/tdee-calculator) for the full picture.
Which formula is more accurate, Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor (1990) is more accurate on modern bodies — it was validated on a larger, more diverse sample and systematically under-estimates less than Harris-Benedict, which dates to 1919. Most clinical dietitians use Mifflin-St Jeor today. The calculator shows Harris-Benedict as a comparison so you can see the spread; for practical use, go with Mifflin-St Jeor.
Does BMR change with age?
Yes — BMR declines roughly 1–2% per decade after age 20, mostly because people tend to lose lean mass as they age. The age term in both formulas captures this: every extra year costs about 5 kcal/day in Mifflin-St Jeor. The best countermeasure is resistance training to preserve muscle.
Is BMR different for athletes or very lean people?
Mifflin-St Jeor is fairly robust across normal BMI ranges but can underpredict BMR in very muscular people (lean mass burns more than fat mass) and overpredict in very high body-fat individuals. If your body composition is unusual, a body-fat-adjusted formula like Katch-McArdle is more precise — but it requires knowing your body-fat percentage.
How do I use BMR for weight loss or gain?
Start with your TDEE (BMR × activity factor — use the [TDEE calculator](/tdee-calculator)). For **weight loss**, eat 300–500 kcal/day below TDEE; for **gain**, eat 200–500 kcal/day above. Track your weight weekly and adjust: if weight isn't moving in the direction you want after 2–3 weeks, your actual TDEE is different from the estimate.