How it works
Your basal metabolic rate (BMR) is the energy your body needs at complete rest to breathe, pump blood, keep warm and repair cells. It is usually 60–70% of all the calories you burn in a day. The calculator gives three well-known estimates.
Mifflin–St Jeor: 10 × kg + 6.25 × cm − 5 × age + 5 (men) or − 161 (women) Harris–Benedict (Roza & Shizgal 1984): men 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age · women 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age Katch–McArdle: 370 + 21.6 × lean mass (kg), lean mass = weight × (1 − body fat %)Worked example. A 28-year-old woman, 62 kg and 165 cm: Mifflin–St Jeor = 620 + 1,031.25 − 140 − 161 = 1,350 kcal a day, about 56 kcal an hour. Harris–Benedict gives 1,411. With 25% body fat, lean mass is 46.5 kg and Katch–McArdle gives 370 + 21.6 × 46.5 = 1,374.
Which formula should I trust?
- Mifflin–St Jeor is the most accurate for most adults in modern studies, which is why it is the main result.
- Harris–Benedict is the classic equation; it tends to read a little higher.
- Katch–McArdle uses lean body mass, so it suits people who know their body fat — especially muscular people, for whom weight-based formulas underestimate.
What changes BMR
Muscle burns more energy than fat, so strength training raises BMR slightly. BMR falls with age (around 1–2% per decade after 20) and when you lose weight. Crash diets can lower it further, which is one reason slow weight loss lasts longer.
BMR is not what you should eat. Multiply it by your activity in the TDEE calculator, set a goal in the calorie calculator, and check your weight range with the ideal weight calculator. This is an estimate, not medical advice.