Basal metabolic rate calculator
Find out how many calories your body burns at rest (BMR) and your maintenance calories based on physical activity, with the Mifflin-St Jeor formula.
What the basal metabolic rate is
The basal metabolic rate (BMR) is the energy your body burns at complete rest for vital functions (breathing, heartbeat, temperature). Maintenance calories (TDEE) add the burn from daily and sporting activity: they are the calories you need to keep your current weight.
How to use it
To lose weight aim a bit below your maintenance calories (e.g. −15/−20%); to gain muscle, a bit above. It's a statistical estimate: consistency over time matters more than the exact number. For health concerns consult a doctor or dietitian.
Why the formula used matters
There are two widespread formulas and they do not give the same number: Harris-Benedict, from 1919 and revised in 1984, and Mifflin-St Jeor, from 1990. On the same person they can differ by one or two hundred calories, and the second is today considered the more reliable across the general population.
Neither of them uses body composition, and that is the limitation: two people of the same weight, height and age get the same result even if one carries far more muscle. Muscle burns more at rest than fat, so the estimate understates people who train and overstates those who do not.
Basal, resting and total are not the same
Basal metabolism is measured under laboratory conditions: on waking, lying down, twelve hours fasted, in a room at neutral temperature. What we usually call resting metabolism is measured under more realistic conditions and comes out 5 to 10% higher.
The number you actually need in order to eat is a third one: total requirement, the basal figure multiplied by an activity factor. That is where the errors concentrate, because almost everybody declares themselves «moderately active» while sitting for nine hours a day.
Metabolism adapts to what you eat
On a prolonged diet expenditure falls by more than the weight loss explains: the body cuts non-essential spending, from spontaneous movement to the temperature of the extremities. It is why after a few months the same deficit stops working.
The defence that holds is keeping muscle mass with strength training and enough protein, and not dropping too far below maintenance. A 15-20% deficit works better over time than a 40% one, which costs muscle too and lowers expenditure further.
Nearby tools
Your requirement with activity included is in Calorie requirement, and the sums for losing weight in Calorie deficit. To split calories between nutrients there is Macronutrients.