BMR is your body's idle draw — the calories burned keeping organs running, brain thinking, and temperature steady if you did nothing all day. It's the foundation every calorie target is built on, and typically 60–70% of your total burn.
The equation and why this one
This calculator uses Mifflin-St Jeor, the 1990 equation the American Dietetic Association found most accurate for healthy adults, retiring the older Harris-Benedict standard. For a 30-year-old man, 178 cm and 82 kg: 10×82 + 6.25×178 − 5×30 + 5 = 1,788 kcal/day — about 75 kcal an hour, even asleep.
Katch-McArdle: when you know your body fat
Weight-based formulas can't tell muscle from fat, so they under-estimate muscular people and over-estimate at high body fat. Katch-McArdle fixes this by pricing lean tissue only: 370 + 21.6 × lean mass (kg). Enter a body-fat percentage — measured, or estimated with the body fat calculator — and it appears alongside for comparison.
From BMR to what you should actually eat
Never eat at BMR — it's the floor, not the target. Digestion and daily movement add on top: multiply by 1.2 (sedentary) to 1.9 (very active) for maintenance calories. That's precisely what the TDEE calculator does, then offers goal-based targets from there.
What moves BMR
Lean mass is the big lever — each kilogram of muscle adds roughly 13–22 kcal/day at rest, which is why resistance training defends metabolism during weight loss. Age drifts it down a few percent per decade; crash dieting suppresses it further. Formulas assume typical physiology: thyroid conditions and medications can move the real number.
Estimates for healthy adults; not medical advice.