What BMR actually measures
Basal metabolic rate is the energy your body spends doing nothing more than staying alive: keeping your heart beating, your lungs working, your brain active and your body temperature stable. It is the single largest slice of most people’s daily calorie burn, typically 60 to 70 percent of the total.
The Mifflin–St Jeor equation used here estimates BMR from weight, height, age and sex. It was published in 1990 and tends to be more accurate for modern populations than the older Harris–Benedict formula, which can overestimate by a few percent.
Turning BMR into daily calories
BMR on its own is the resting figure. To estimate the calories you actually burn in a day you multiply it by an activity factor that reflects how much you move, which gives your total daily energy expenditure (TDEE).
- Sedentary (little exercise): BMR × 1.2
- Lightly active (1–3 days a week): BMR × 1.375
- Moderately active (3–5 days a week): BMR × 1.55
- Very active (6–7 days a week): BMR × 1.725
Why your real number may differ
Equations work from population averages, so two people with identical stats can have BMRs that differ by a few hundred calories. Muscle mass, body composition, hormones, genetics and medications all shift the figure.
If you are tracking calories, treat the estimate as a starting point. Watch how your weight responds over two to three weeks and adjust intake rather than trusting the formula to the last calorie.
A note on health
This estimate is for general fitness and nutrition planning, not medical advice. If you have a thyroid condition, are pregnant, are recovering from illness, or are managing weight for a clinical reason, speak to a doctor or registered dietitian before setting calorie targets.
Formula
bmr = 10·kg + 6.25·cm − 5·age + (5 male / −161 female)