BMR Calculator
Your Basal Metabolic Rate is the energy your body needs just to stay alive — breathing, circulating blood, keeping cells running — if you did nothing but lie still for 24 hours. Every other calorie estimate builds on this number.
Used because it changes the formula's constant — not a statement about identity.
Enter your details to see how many calories your body burns at rest.
How it's calculated
Wellnum uses the Mifflin-St Jeor equation, published in 1990 and validated against measured metabolic rates in later studies, which most dietitians consider more accurate than the older 1919 Harris-Benedict formula for the general population:
Men: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5
Women: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161
This is your resting number — it doesn't include the calories burned by daily movement or exercise. For that, see the daily calorie calculator, which applies an activity multiplier on top of your BMR.
A worked example
Take a 30-year-old woman who is 165 cm tall and weighs 60 kg: BMR = (10 × 60) + (6.25 × 165) − (5 × 30) − 161 = 600 + 1,031 − 150 − 161 = 1,320 kcal. That's roughly what her body would burn lying in bed all day doing nothing but staying alive — breathing, circulating blood, maintaining body temperature, and repairing cells. Almost nobody actually eats at this number; it's a baseline you build on top of, not a daily target.
What actually drives your BMR
Four things move this number more than anything else. Body size is the biggest — taller, heavier people simply have more tissue to maintain, so BMR scales up with weight and height, which is why the formula uses both. Muscle mass matters almost as much: a kilogram of muscle burns noticeably more energy at rest than a kilogram of fat, so two people at the same weight can have meaningfully different BMRs if one carries more lean mass. Age works against you slowly — BMR tends to drift down roughly 1–2% per decade past your twenties, mostly because muscle mass declines unless it's actively maintained through resistance training. And sex plays a role too, which is why the formula has separate equations — men typically carry more muscle mass at the same height and weight, which the −161 versus +5 constant partly accounts for.
Why "starving" yourself backfires
Eating well below your BMR for extended periods can trigger what researchers call adaptive thermogenesis — your body senses a prolonged shortfall and quietly turns down its own energy expenditure to compensate, partly by reducing non-essential processes and partly through muscle loss (muscle is metabolically expensive to maintain, so the body sheds it under sustained restriction). The practical result is a slower metabolism that makes further weight loss harder and rebound weight gain more likely once normal eating resumes. This is the biological argument for a moderate deficit over a crash one — see the calorie calculator for sustainable targets.
Frequently asked questions
What is BMR and why does it matter?
Basal Metabolic Rate is the energy your body burns at complete rest just to keep essential functions running — breathing, circulation, cell repair. It's usually 60–75% of your total daily calorie burn, so it's the number every calorie or diet target should start from.
How is BMR different from TDEE?
BMR is your resting number alone. TDEE (Total Daily Energy Expenditure) is BMR adjusted for how active you actually are — desk job versus manual labour, sedentary versus training twice a day. See the daily calorie calculator for your TDEE.
Does BMR decrease with age?
Yes, gradually — typically 1–2% per decade after your twenties. Muscle mass tends to decline with age unless actively maintained through resistance training, and since muscle burns more energy at rest than fat, BMR drifts down over the decades even if body weight stays the same.
Which BMR formula does Wellnum use?
The Mifflin-St Jeor equation, published in 1990, which most dietitians consider more accurate than the older Harris-Benedict formula for the general population. It's also the equation most commonly used in clinical nutrition practice today.
Can I eat below my BMR to lose weight faster?
You can, but it's usually counterproductive past the short term. Sustained eating well below BMR can slow your metabolism through a process called adaptive thermogenesis and accelerate muscle loss, both of which make long-term weight management harder rather than easier.
Does building muscle raise my BMR?
Yes, modestly. Muscle tissue burns more energy at rest than fat tissue, so adding muscle through resistance training nudges your BMR upward over time. It's a slow lever — a few extra kilograms of muscle might add roughly 50–100 kcal to daily BMR — but it compounds over years and helps offset the natural age-related decline.