Calorie Calculator

Two-step process. First, compute BMR (Basal Metabolic Rate) — calories burned at rest, just keeping you alive (breathing, circulation, brain, organ function). Then multiply by an activity factor that accounts for movement.

Mifflin-St Jeor (1990, the standard since 2005): BMR_men = 10×weight(kg) + 6.25×height(cm) − 5×age(years) + 5. BMR_women = 10×weight(kg) + 6.25×height(cm) − 5×age(years) − 161. The "+5/−161" tail accounts for average body composition differences. For known body composition, Katch-McArdle (BMR = 370 + 21.6×lean_mass_kg) is more accurate.

• Activity factor 1.2 (sedentary) — desk job, no exercise. Most office workers.
• Activity factor 1.375 (lightly active) — 1-3 sessions of light exercise/week.
• Activity factor 1.55 (moderately active) — 3-5 moderate sessions/week.
• Activity factor 1.725 (very active) — 6-7 hard sessions/week.
• Activity factor 1.9 (extremely active) — physical job + daily training.

• Activity factor is the biggest source of error. People consistently overestimate their activity level. "Moderately active" requires consistent intentional exercise; a daily walk + the gym occasionally is "lightly active" at best.
• Body composition matters. Two people with identical height, weight, age can differ in muscle mass by 10+ kg. The muscular one burns 200-400 more kcal/day at rest. Formulas using weight (not lean mass) average them out.
• Genetic variation in BMR is ±10-15% from the population mean. Some people just burn fewer or more calories than the formula predicts.
• NEAT (non-exercise activity thermogenesis) — fidgeting, posture changes, walking around the kitchen — varies wildly between individuals (300+ kcal/day spread). Underweight people often have high NEAT; "I just have a fast metabolism" usually means high NEAT, not a different BMR.
• Adaptive thermogenesis — sustained calorie restriction lowers BMR below the formula's prediction. Heavy dieters at goal weight often need 10-20% fewer calories to maintain than the calculator says they should.

• Treat TDEE as a starting estimate, not a prescription. Eat at the estimated maintenance for 2 weeks, track weight; if stable, the estimate is good. If you gain or lose, adjust by ~100-200 kcal/day until stable.
• For weight loss, 300-500 kcal/day deficit is sustainable for most people. 750+ kcal/day deficit is harder to maintain and risks muscle loss without sufficient protein and resistance training.
• For muscle gain, +200-300 kcal/day above maintenance is the textbook "lean bulk" range. More than that produces faster weight gain but more of it is fat.
• For maintenance after weight loss, expect to maintain at 5-15% fewer calories than the calculator predicts for your new weight. Adaptive thermogenesis is real.

• You are starting a diet or fitness program and want a starting calorie target instead of a generic "1500 for women, 2000 for men".
• You finished a cut and want to know your new maintenance calories.
• You are evaluating a tracker app's estimated TDEE against an independent formula.
• You are curious about the math behind "calorie deficit for weight loss" and want to see the numbers for your specific stats.

• It will not measure your real BMR. Indirect calorimetry (in a lab, breathing into a mask for 30 minutes) gives ±2% accuracy. Formulas give ±10-15%. If you need precision, get tested.
• It will not give medical advice. Severe calorie restriction, eating disorders, and chronic conditions require professional guidance — not a calculator.
• It will not account for medication, thyroid conditions, PCOS, recent significant weight changes, or other factors that meaningfully alter metabolism beyond the formula's assumptions.