BMR Calculator
How This Calculator Works
We use the Mifflin-St Jeor equation, which is the standard predictive formula used by registered dietitians and clinical nutritionists. It takes weight, height, age, and sex, and outputs your basal metabolic rate.
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161Citation: Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. "A new predictive equation for resting energy expenditure in healthy individuals." American Journal of Clinical Nutrition, 1990;51(2):241–247.
What Your BMR Tells You
Your BMR is the floor — the minimum daily calories your body needs just to function. It's the starting point for every calorie target. Multiply by 1.2–1.9 (depending on activity) to get your TDEE, the number you actually eat against. Eating below your BMR for long stretches is generally not recommended outside medical supervision.
Limitations
Population averages: about 10% accurate for most healthy adults. Less accurate for very muscular people (real BMR usually higher than predicted) and for people with significantly above-average body fat (real BMR usually lower). Clinical measurement requires indirect calorimetry — not something most of us have access to.
Frequently Asked Questions
What is BMR?
BMR — Basal Metabolic Rate — is the energy your body burns at rest, just to keep you alive. Heart beating, lungs breathing, brain thinking, organs doing their thing. Most adults have a BMR between 1,200 and 2,000 kcal per day. It's the floor; everything else you do (walking, working, exercising) adds on top.
Is BMR the same as RMR?
Almost. BMR (basal metabolic rate) is technically measured after an overnight fast in a thermoneutral room while you're lying perfectly still. RMR (resting metabolic rate) is measured under less strict conditions and runs about 10% higher. In casual use the terms get swapped, but the Mifflin-St Jeor equation actually predicts RMR — though everyone calls it BMR.
Why do I need to know my BMR?
BMR is the foundation of any calorie target. Multiply it by an activity factor and you get TDEE — your full-day calorie burn. Subtract a deficit from TDEE and you get a fat-loss target. Knowing your BMR also tells you the lower bound: eating below BMR for long stretches is generally not recommended without medical supervision.
Why is the Mifflin-St Jeor equation considered the best?
A 2005 review by the American Dietetic Association compared common predictive equations (Harris-Benedict, Mifflin-St Jeor, Owen, WHO) against measured BMR in healthy adults and found Mifflin-St Jeor was the most accurate, especially for non-obese adults. It's been the dietetic standard ever since.
Does muscle increase BMR?
Yes, but less than people think. Muscle tissue burns roughly 6 kcal per pound per day at rest, versus about 2 kcal per pound for fat. So adding 10 lb of muscle adds maybe 40 extra kcal per day to your BMR — meaningful over time, but not a license to eat 500 extra kcal because you started lifting.
Does BMR drop with age?
Yes. BMR declines roughly 1–2% per decade after age 20, partly from natural muscle loss (sarcopenia) and partly from changes in organ tissue. The Mifflin-St Jeor equation builds this in — older inputs return lower BMR. Strength training is the most effective way to slow the decline.
Should I eat at my BMR?
Generally no, unless you're under medical supervision. BMR is what you'd burn lying motionless all day. Real life involves at least some walking and movement, so a healthier minimum target is BMR × 1.2 (sedentary TDEE). For women, eating below ~1,200 kcal/day is generally not recommended; for men, ~1,500 kcal/day.
How accurate is this calculator?
Accurate within roughly 10% for most healthy adults. It can be less accurate at the extremes — very muscular people may have a higher real BMR than the equation predicts, and people with significantly above-average body fat may have a lower real BMR. For clinical accuracy you'd need indirect calorimetry, which requires a metabolic chamber or hood.