OneTaskBy Tim King · Updated
BMR Calculator
Resting Calorie Burn by Three Formulas, Plus Daily Calorie Needs
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How the BMR Calculator works
This BMR calculator works out your basal metabolic rate, the calories your body burns at complete rest just to stay alive. It compares the Mifflin-St Jeor and revised Harris-Benedict equations, adds Katch-McArdle when you know your body fat percentage, and turns the result into daily calorie needs for five activity levels.
Basal metabolic rate covers breathing, circulation, keeping warm and repairing cells. For most people it is 60% to 70% of everything they burn in a day, so it is the foundation of any calorie target. Exercise and daily movement are added on top through an activity multiplier.
How the BMR calculator works
The Mifflin-St Jeor formula is BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age, plus 5 for men or minus 161 for women. The revised Harris-Benedict equation from 1984 uses different weights for the same inputs. Katch-McArdle ignores sex and age and uses lean mass only: BMR = 370 + 21.6 × lean body mass in kg, which suits lean, muscular people better.
First example. A 30-year-old man, 180 cm and 80 kg: 800 + 1,125 − 150 + 5 = 1,780 kcal a day by Mifflin-St Jeor, and 1,854 kcal by Harris-Benedict.
Second example. A 35-year-old woman, 5'5" and 140 lb with 25% body fat, has 47.6 kg of lean mass, so Katch-McArdle gives 370 + 21.6 × 47.6 = 1,399 kcal a day.
How many calories do I burn doing nothing? Your BMR, spread over 24 hours: 1,780 kcal is about 74 kcal an hour, roughly the energy of a small banana.
BMR by weight for a 40-year-old woman (165 cm) and man (178 cm), kcal per day
| Weight (kg) | Woman, Mifflin | Woman, Harris-Benedict | Man, Mifflin | Man, Harris-Benedict |
|---|---|---|---|---|
| 45 | 1,120 | 1,202 | 1,368 | 1,318 |
| 50 | 1,170 | 1,248 | 1,418 | 1,385 |
| 55 | 1,220 | 1,294 | 1,468 | 1,452 |
| 60 | 1,270 | 1,340 | 1,518 | 1,519 |
| 65 | 1,320 | 1,387 | 1,568 | 1,586 |
| 70 | 1,370 | 1,433 | 1,618 | 1,653 |
| 75 | 1,420 | 1,479 | 1,668 | 1,720 |
| 80 | 1,470 | 1,525 | 1,718 | 1,787 |
| 85 | 1,520 | 1,572 | 1,768 | 1,854 |
| 90 | 1,570 | 1,618 | 1,818 | 1,921 |
| 95 | 1,620 | 1,664 | 1,868 | 1,988 |
| 100 | 1,670 | 1,710 | 1,918 | 2,055 |
| 105 | 1,720 | 1,756 | 1,968 | 2,122 |
| 110 | 1,770 | 1,803 | 2,018 | 2,189 |
| 115 | 1,820 | 1,849 | 2,068 | 2,256 |
| 120 | 1,870 | 1,895 | 2,118 | 2,323 |
| 125 | 1,920 | 1,941 | 2,168 | 2,390 |
| 130 | 1,970 | 1,988 | 2,218 | 2,457 |
| 135 | 2,020 | 2,034 | 2,268 | 2,524 |
| 140 | 2,070 | 2,080 | 2,318 | 2,591 |
Tips and pitfalls
- Mifflin-St Jeor is the default. Studies comparing equations against measured metabolism find it the most accurate for most adults, typically within 10%.
- Add body fat if you know it. For athletes and very lean people, Katch-McArdle tracks muscle better than height and weight do.
- BMR is not your calorie target. Eating at BMR leaves nothing for daily movement. Use the activity table, or the TDEE calculator, for a daily figure.
- Equations are estimates. Genetics, hormones and recent dieting can shift real metabolism by a few hundred calories either way.
FAQ
What is a normal BMR?
For adults, BMR usually falls between about 1,200 and 1,500 kcal a day for women and 1,500 to 1,900 kcal for men. Bigger, taller and more muscular people sit higher, and the figure falls gently with age, by roughly 50 kcal per decade on the Mifflin-St Jeor scale.
What is the difference between BMR and RMR?
Basal metabolic rate is measured under strict conditions: fully rested, fasted and at a neutral temperature. Resting metabolic rate is measured more casually and runs about 10% higher. In everyday use the two terms are treated as the same, and these formulas estimate both.
Which BMR formula is most accurate?
For most adults Mifflin-St Jeor comes closest to measured values, which is why dietitians default to it. Harris-Benedict tends to read a little high. Katch-McArdle can beat both for lean, muscular people, but only if the body fat figure you enter is accurate.
How do I increase my BMR?
Building muscle is the main lever, since lean tissue burns more at rest than fat does. Strength training, enough protein and avoiding long crash diets all help. The effect is modest though: each extra kilogram of muscle adds only about 13 kcal a day.
Does BMR go down when you lose weight?
Yes. A smaller body needs less energy, so BMR falls as weight comes off, and long periods of heavy dieting can lower it a little further. Recalculate after every few kilograms lost so your calorie target keeps matching your current body.
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