BMR Calculator
Work out your basal metabolic rate — the calories your body burns at complete rest — from the Mifflin-St Jeor equation, and see what the older Harris-Benedict equation predicts for the same body. Metric and imperial units are both supported.
Both equations predict resting energy within about 10% on average, and the two usually land within 5% of each other. The activity table applies your selected BMR; the Calorie and TDEE calculators use the same factors with Mifflin-St Jeor.
Formula and calculation
Worked example
A 30-year-old man, 180 cm and 80 kg: Mifflin-St Jeor gives BMR = 10×80 + 6.25×180 − 5×30 + 5 = 1,780 kcal/day. The 1984 revision of Harris-Benedict gives 1,854 kcal/day, about 4.14% higher. Scaling the Mifflin figure by the moderate activity factor 1.55 puts daily maintenance near 2,759 kcal.
What moves your BMR, and what does not
Body size and composition drive BMR: muscle and organs burn more at rest than fat does, so two people of the same weight can differ by a few hundred calories. It also declines slowly with age, and long, aggressive diets can push it 10% or more below prediction while you are still dieting. Fever, pregnancy and cold weather raise it. What barely moves it: spicy food, green tea and supplements sold for "metabolism". Their effect is small next to the error already in the estimate, so do not build a diet around them.
What the results mean
- BMR
- Basal metabolic rate — the calories your body would burn in a full day of complete rest, from the equation you selected. Everything you do on top of resting adds to this number.
- Mifflin-St Jeor
- The same BMR from the Mifflin-St Jeor equation (1990), the one dietitians normally recommend for adults. Shown for comparison whichever equation you picked above.
- Harris-Benedict (revised)
- BMR from the Harris-Benedict equation as revised in 1984. At typical body sizes it reads 4–6% higher than Mifflin-St Jeor, which is why two calculators can disagree about your metabolism.
- Difference between the two equations
- How far apart the two equations are, as a percentage of the Mifflin-St Jeor figure. A gap under about 10% is smaller than the day-to-day error in any BMR estimate, so it is not worth choosing an equation over.
Frequently asked questions
What is the difference between BMR and RMR?
BMR is measured under strict lab conditions — fasted, lying still, comfortably warm, first thing in the morning. RMR (resting metabolic rate) is measured more loosely, and because the conditions are easier it usually comes out 5–10% higher. Most calculators, including this one, predict something between the two and label it BMR.
How do I turn BMR into the calories I can eat?
Multiply it by an activity factor: 1.2 sedentary, 1.375 light exercise, 1.55 moderate, 1.725 active, 1.9 very active. That gives your TDEE, the calories you burn in a full day. Eating at your TDEE holds your weight steady — the activity table on this page does the multiplication for you.
Which BMR equation should I use?
Mifflin-St Jeor, for almost everyone. It was derived on modern populations and predicts measured energy use more closely, especially for people with obesity. Harris-Benedict, revised in 1984, reads about 5% higher at typical body sizes — and the gap widens for older or heavier bodies, where the older equation overestimates more.
Can I just eat my BMR to lose weight?
No, not for long. BMR is what you burn lying still, so eating only that much leaves nothing for walking, working or digesting, and the deficit is usually larger than you intended. Practical targets come off TDEE, and intakes under about 1,200 kcal (women) or 1,500 kcal (men) should be supervised by a doctor.