BMR calculator: your basal metabolic rate
This free BMR calculator estimates your basal metabolic rate, the calories your body burns at complete rest, with three published formulas side by side: Mifflin-St Jeor, revised Harris-Benedict and, when you enter your body-fat percentage, Katch-McArdle. A table then multiplies your BMR by the conventional activity factors to show daily calories, in kg or lb. Nothing you type is stored.
The three differ because each was fitted to a different sample and uses different inputs: Mifflin-St Jeor (1990) and revised Harris-Benedict (1984) work from height, weight, age and sex, while Katch-McArdle ignores all of those and uses only lean body mass.
Daily calories by activity level (Mifflin-St Jeor × factor)
| Activity level | Multiplier | Calories per day |
|---|---|---|
| SedentaryLittle or no exercise, desk job | BMR × 1.2 | — |
| LightExercise 1-3 days a week | BMR × 1.375 | — |
| ModerateExercise 3-5 days a week | BMR × 1.55 | — |
| ActiveHard exercise 6-7 days a week | BMR × 1.725 | — |
| Very activeHard daily training or a physical job | BMR × 1.9 | — |
That row is your maintenance intake. For cut and bulk targets built on it, use the TDEE calculator.
Values recalculate instantly as you type. Nothing is sent or stored — the math runs in your browser.
How the calculation works
Each formula predicts resting energy expenditure from a few body measurements, because measuring it directly needs indirect calorimetry: a mask or hood that analyses the oxygen you consume and the carbon dioxide you produce while lying still. The equations were fitted to people measured that way, so they return the average BMR of someone with your numbers. The calculator shows all three so you can see how much the choice of equation moves the answer.
Mifflin-St Jeor (1990, the most accurate for the general population; derived from 498 healthy adults aged 19 to 78 measured by indirect calorimetry — Mifflin et al., Am J Clin Nutr 51:241-247):
Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Revised Harris-Benedict (the 1919 equations re-fitted by Roza & Shizgal, 1984, Am J Clin Nutr 40:168-182):
Men: 88.362 + (13.397 × weight kg) + (4.799 × height cm) − (5.677 × age)
Women: 447.593 + (9.247 × weight kg) + (3.098 × height cm) − (4.330 × age)
Katch-McArdle (one equation for both sexes, from lean body mass; as printed in Frontiers in Nutrition, 2025):
BMR = 370 + (21.6 × lean body mass kg), where lean body mass = weight kg × (1 − body fat % ÷ 100)
From BMR to daily calories
BMR is what you burn lying still; everything you do on top of it is added with an activity factor. The table multiplies your Mifflin-St Jeor result by the five conventional multipliers (1.2, 1.375, 1.55, 1.725 and 1.9) used by most calculators. They are rules of thumb, not measurements, and the largest source of error in any daily estimate: if you sit most of the day and train a few times a week, the 1.375 row is usually the honest one. The product is your total daily energy expenditure, or maintenance calories; the TDEE calculator builds cut and bulk targets from it.
BMR versus RMR
Basal metabolic rate is defined under strict conditions: measured after a night's sleep, fasted, at rest, in a temperature-neutral room. Resting metabolic rate is measured under everyday conditions and comes out a little higher because some digestion and recent activity leak in. The Mifflin-St Jeor and Harris-Benedict studies measured resting energy expenditure, so strictly their output is RMR; the difference is small enough that calculators, including this one, use the terms interchangeably.
Limits of the estimate
Every formula is a statistical estimate: two people with identical height, weight, age and sex can differ in BMR because of lean mass, thyroid function, genetics and how long they have been dieting, which lowers expenditure through metabolic adaptation. Katch-McArdle only helps if your body-fat figure is reliable; a smart-scale reading can be off by several points, and that error goes straight into the result. None of the formulas is valid during pregnancy or breastfeeding, for people under 18, for elite athletes or with metabolic conditions — in those cases the reference should come from a healthcare professional. The way to refine the number is to log what you eat for two or three weeks and compare it with how your weight actually moves.
Frequently asked questions
What is BMR?
Basal metabolic rate is the energy your body uses at complete rest to keep organs working, hold its temperature and repair cells: breathing, circulation, brain activity. It is measured after a night's sleep, fasted, in a temperature-neutral room. For most adults it is the largest part of daily calorie burn, before digestion and any movement are added.
Can I just eat my BMR to lose weight?
You would lose weight, because you burn more than your BMR every day, but it is not a target most people should plan around. BMR is the floor of your expenditure; deficits are taken from your total daily expenditure (TDEE) instead. Eating at BMR often lands below 1,200 kcal for women or 1,500 kcal for men, an intake that should be supervised.
What is the most accurate BMR calculator?
Any calculator that applies Mifflin-St Jeor to your correct height, weight, age and sex gives the same answer; the site does not matter. That equation was derived from 498 healthy adults measured by indirect calorimetry and predicted their resting expenditure better than the 1919 Harris-Benedict. If you know your body fat, Katch-McArdle can be closer for lean or very muscular people.
Can a fitness tracker or smartwatch tell me my BMR?
Watches estimate it with a formula like this one; they do not measure it. They take the height, weight, age and sex in your profile and multiply. A measured BMR requires indirect calorimetry, equipment that analyses the oxygen you consume at rest. What trackers add is something the formula cannot: an estimate of your daily activity, which turns BMR into total expenditure.
How many calories should I eat if my BMR is 1500 to lose weight?
Start from total expenditure, not from BMR. With a BMR of 1,500 kcal, maintenance is about 1,800 kcal if you are sedentary (× 1.2) and about 2,325 kcal with moderate exercise (× 1.55). A 300 to 500 kcal deficit means roughly 1,300 to 1,500 kcal sedentary or 1,825 to 2,025 kcal active. The sedentary figure sits at or below the intake floors, so adding activity is the safer lever.
Should I eat 500 calories less than my BMR to lose weight?
No. The 500 kcal rule subtracts from total daily energy expenditure (TDEE), which already includes your BMR plus everything you do; subtracting from BMR itself doubles the cut. For a woman with a BMR of 1,400 kcal that would mean 900 kcal a day, well under the 1,200 kcal floor. Calculate your TDEE with the multipliers above, then take the deficit from that.
What is the difference between BMR and RMR?
Basal metabolic rate is measured under strict conditions: fasted, rested, after sleep, in a temperature-controlled room. Resting metabolic rate is measured under looser conditions and comes out slightly higher because it includes a little digestion and recent activity. The equations on this page were fitted to resting measurements, so many sources call their output RMR; in everyday use the two terms are interchangeable.
Keep reading
TDEE calculator · Daily calorie calculator with macros · Where the 1,200 and 1,500 calorie floors come from · How many calories should I eat per day? · Energy balance: the full ledger
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