CalcVitalsBMR Calculator — Basal Metabolic Rate
BMR is the energy your body spends just staying alive — breathing, circulating blood, holding temperature. The Mifflin-St Jeor equation gives a man of 70 kg, 175 cm and 30 years a BMR of 1,649 kcal a day. Everything you actually do is added on top of that floor.
How it works
Lie still, awake, fed yesterday, in a comfortable room, doing nothing at all — your body still burns a surprising amount of energy. Your brain alone takes about a fifth of it; the liver, heart and kidneys, all small organs, burn far above their weight class. That floor of energy use is your basal metabolic rate, and for most people it is the largest single slice of their daily calorie expenditure — bigger than exercise, usually bigger than everything else combined.
Of the prediction equations, Mifflin-St Jeor (1990) has repeatedly tested closest to measured values in modern adults, which is why it leads this page and why dietitians default to it. The older Harris-Benedict equation, shown alongside, tends to read a little higher. Both are population averages wearing your clothes: two people with identical inputs can genuinely differ by a couple of hundred kilocalories.
BMR is a floor, not a budget. Nobody should eat at their BMR expecting to function — it excludes digestion, movement, work and thought. To turn it into a daily calorie figure, multiply by an activity factor, which is exactly what the TDEE calculator next door does.
The method
Mifflin-St Jeor (1990): men BMR = 10·W + 6.25·H − 5·A + 5; women = 10·W + 6.25·H − 5·A − 161 (W kg, H cm, A years). Harris-Benedict revised (Roza & Shizgal 1984) shown for comparison.
Frequently asked questions
What is the difference between BMR and RMR?
Resting metabolic rate is measured under looser conditions (not fully fasted or rested) and reads about 3–10% higher. In everyday use — and on most calculator sites — the two are treated as near enough the same number.
Does BMR fall with age?
Yes, mostly through lost muscle: the equation's −5 kcal per year captures the average drift. Resistance training and adequate protein blunt it, because what is really falling is lean mass, not some metabolic clock.
Can I raise my BMR?
Only modestly, and mainly by adding muscle — each kilogram of muscle burns roughly 13 kcal a day at rest, against about 4.5 for fat. The effect is real but small; BMR is mostly set by your size, sex and age.
Should I eat exactly my BMR to lose weight?
No. BMR assumes complete rest in bed. Eating at BMR while living a normal life creates a much larger deficit than intended and is a common route to fatigue and muscle loss.