BMR Calculator
Basal metabolic rate is what the body spends keeping you alive — breathing, circulation, staying warm. It is roughly two thirds of most people's daily total, which is why exercise moves the number less than people expect.
Resting calories
1,755a day
- Mifflin-St Jeor
- 1,755 cal
- Harris-Benedict
- 1,825 cal
- Sedentary (x1.2)
- 2,106 cal
- Light (x1.375)
- 2,413 cal
- Moderate (x1.55)
- 2,720 cal
- Active (x1.725)
- 3,027 cal
- Athlete (x1.9)
- 3,335 cal
- Basal rate is what the body spends doing nothing at all — breathing, circulation, keeping warm. It is roughly two thirds of most people's daily total, which is why exercise moves the number less than people expect.
- The two formulas disagree by a few per cent and Mifflin-St Jeor is generally the more accurate of them. Neither accounts for body composition, so both understate a very muscular person and overstate a very sedentary one.
- Treat any of these as a starting figure to test against reality. Track what you actually eat and what your weight does for a fortnight, and the truth will be within a few hundred calories of one of them.
About the BMR calculator
Your body spends most of its energy on being a body. Heart, lungs, liver, kidneys and brain run continuously, and together they account for the majority of what you burn before you move at all. An 80kg man of 35 at 180cm has a basal rate of around 1,755 calories — spent lying still.
Two formulas are in wide use and they disagree by a few per cent. Mifflin-St Jeor dates from 1990 and is generally the more accurate; Harris-Benedict is from 1919, revised in 1984, and usually reads a little higher. Both are shown here because the gap between them is a fair indication of how precise either can be.
Neither knows anything about body composition, which is their real limitation. Muscle burns more at rest than fat does, so both formulas understate a very muscular person and overstate a very sedentary one of the same weight. If you know your body fat percentage, a lean-mass formula will do better.
The activity multipliers turn a basal rate into a daily total, and they are blunter still. The gap between sedentary and athlete is more than a thousand calories on these figures, and most people place themselves a level too high.
Treat any of this as a starting figure to test. Track what you actually eat and what your weight does over a fortnight, and reality will land within a couple of hundred calories of one of these numbers.
What it works out
- Basal rate by both formulas in common use
- Daily needs at five activity levels
- Metric or imperial measurements
The formula
Mifflin-St Jeor: BMR = 10w + 6.25h − 5a + s (s = +5 male, −161 female)
Weight in kilograms, height in centimetres, age in years. The sex constant is where the two versions of the formula differ, and it accounts for the difference in average body composition rather than anything else.
For an 80kg, 180cm man of 35: 800 + 1,125 − 175 + 5 = 1,755 calories a day at complete rest.
Harris-Benedict uses different coefficients and gives 1,825 for the same person — four per cent higher. Neither is authoritative. The spread is the useful information: any single figure implies a precision these formulas do not have.
Multiplying by an activity factor gives the daily total. Sedentary is 1.2, athlete is 1.9, and the honest answer for most desk workers who train a few times a week is somewhere around 1.375 to 1.55 — lower than they would like to pick.
- w
- Weight in kilograms.
- h
- Height in centimetres.
- a
- Age in years. The rate falls with age, largely through lost muscle.
- s
- The sex constant: +5 for men, −161 for women.
A worked example
A 35-year-old man, 80 kilograms and 180 centimetres.
That works out to 1,755 a day.
- Mifflin-St Jeor
- 1,755 cal
- Harris-Benedict
- 1,825 cal
- Sedentary (x1.2)
- 2,106 cal
- Light (x1.375)
- 2,413 cal
- Moderate (x1.55)
- 2,720 cal
- Active (x1.725)
- 3,027 cal
- Athlete (x1.9)
- 3,335 cal
Questions
What is BMR?
The energy your body uses at complete rest — breathing, circulation, cell repair, staying warm. It is what you would burn lying still all day, and for most people it is around two thirds of the daily total.
What is the difference between BMR and TDEE?
BMR is at rest. Total daily energy expenditure is BMR multiplied by an activity factor, so it includes everything you do. TDEE is the number to eat against; BMR is the number it is built from.
Which formula should I use?
Mifflin-St Jeor is generally the more accurate and is the modern default. Harris-Benedict is older and usually reads a few per cent higher. If you are unusually muscular, a formula based on lean mass will beat both.
Why does BMR fall with age?
Mostly through lost muscle rather than age itself. Muscle costs more to maintain than fat, and people carry less of it each decade unless they train. Resistance training slows the decline substantially.
Can I eat at my BMR to lose weight?
It is more aggressive than it sounds, because you burn well above BMR just by being awake and moving. Eating at basal rate is typically a deficit of several hundred calories a day, and going below it makes adequate nutrition difficult.
How accurate is this?
Within about ten per cent for most people, which is a couple of hundred calories. The formulas cannot see body composition, so they are least accurate at the extremes — very muscular or very sedentary.
Which activity level should I pick?
Lower than you think. Sedentary covers a desk job with little exercise; moderate means genuinely training three to five days a week. Most people overestimate by one level, which is several hundred calories.