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What your body spends doing nothing.
Basal metabolic rate is the energy cost of simply being alive: breathing, circulating blood, keeping your temperature up, repairing tissue. It is the floor everything else is built on, and for most people it is the largest single part of the day.
Everything here runs in your browser. Nothing you enter is uploaded, nothing is stored, and there is no sign-up. These are estimates from published equations, not medical advice.
What is BMR, and what does it actually measure?
Basal metabolic rate is what your body burns at complete rest, doing nothing at all. It covers breathing, circulation, body temperature, brain activity and tissue repair. For most people it accounts for roughly 60 to 70 percent of everything they burn in a day, which is why it dominates the total.
Strictly, BMR is measured after an overnight fast, lying still, in a temperature-controlled room. What a calculator gives you is an estimate of resting energy expenditure, which runs a few percent higher and is close enough for every practical purpose outside a lab.
How do you calculate BMR?
This page uses the Mifflin-St Jeor equation, published in 1990. For men it is 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age, plus 5. For women the final term is minus 161 instead. Nothing else goes in.
The older Harris-Benedict equation, published in 1919 and revised in 1984, tends to overestimate for modern body compositions, which is why most dietitians moved to Mifflin-St Jeor. Katch-McArdle is more accurate again, but it needs a measured body fat percentage that most people do not have.
What is the difference between BMR and TDEE?
BMR is the resting cost. TDEE is the whole day. TDEE is your BMR multiplied by an activity factor between 1.2 and 1.9, so it is always the larger number. Nobody burns only their BMR, because standing up, walking and digesting food all cost energy on top.
This matters because eating at your BMR is not the same as eating at maintenance. It would be a steep deficit for almost anyone. If you want the number to eat at, use the TDEE calculator or the full calorie calculator instead.
Can you change your BMR?
A little, and slowly. Carrying more lean mass raises it, because muscle costs more to maintain than fat, though the effect is smaller than most people expect at roughly 13 calories per kilo of muscle per day. Age lowers it. Crash dieting lowers it temporarily too.
The practical lever is not your BMR, it is the activity factor sitting on top of it. Moving the multiplier from 1.2 to 1.375 is worth more calories for most people than a year of training would add through lean mass alone.
What does a typical BMR look like?
For adults of average height, resting energy usually lands between about 1,200 and 1,900 calories a day. A 30-year-old woman at 170 cm and 70 kg comes out at 1,452. A 30-year-old man at 180 cm and 80 kg comes out at 1,780. Age and body size move it more than anything else.
| Person | BMR | Sedentary day |
|---|---|---|
| Woman, 30, 170 cm, 70 kg | 1,452 kcal | 1,740 kcal |
| Woman, 50, 160 cm, 65 kg | 1,239 kcal | 1,490 kcal |
| Man, 30, 180 cm, 80 kg | 1,780 kcal | 2,140 kcal |
| Man, 50, 175 cm, 90 kg | 1,779 kcal | 2,130 kcal |
Every figure above comes from the same equation this page runs. Put your own numbers in the fields and it will do the same arithmetic.
FAQ
Should I eat my BMR number of calories?
No. Eating at your BMR would be a significant deficit for almost anyone, because it ignores everything you do while awake. Use your TDEE as the reference point, then subtract from that if you want to lose weight.
Why does BMR fall as you get older?
Partly lean mass, which tends to decline from around the fourth decade unless it is trained for, and partly changes in tissue metabolic rate. The Mifflin-St Jeor equation reflects this by subtracting 5 calories for each year of age.
Is BMR different for men and women?
Yes, and the equation handles it with a constant: plus 5 for men, minus 161 for women. At the same weight, height and age that is a gap of 166 calories a day, largely reflecting average differences in body composition.
Sources
- Mifflin MD et al., A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition, 1990
- Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Protein and Amino Acids, National Academies
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