Calories you actually need,
per day.

Field guide

BMR, TDEE, and what they actually mean.

Two acronyms drive every calorie calculator: BMR (Basal Metabolic Rate) and TDEE (Total Daily Energy Expenditure). BMR is the energy your body burns at complete rest — the cost of staying alive. TDEE is BMR multiplied by an activity factor: it's the total calories you actually expend in a typical day, including movement and digestion.

The Mifflin-St Jeor equation (default)

Published in 1990 and validated extensively against indirect calorimetry, the Mifflin-St Jeor formula is the most accurate BMR equation for the general adult population. The Academy of Nutrition and Dietetics recommends it as the standard of practice.

Revised Harris-Benedict (alternate)

The 1919 Harris-Benedict equations were updated in 1984 by Roza and Shizgal with modern data. Slightly less accurate than Mifflin-St Jeor on average, but historically dominant and still widely cited.

Katch-McArdle (when you know your body fat)

If you have a measured body fat percentage, Katch-McArdle beats both alternatives because it works from lean body mass rather than total weight — the same metabolic logic that makes a 200-lb athlete and a 200-lb sedentary office worker have very different needs.

The activity multipliers

Once you have BMR, multiply by an activity factor to get TDEE. These multipliers haven't changed since they were published with the 1985 WHO/FAO/UNU report.

• Sedentary (×1.2): desk job, no exercise
• Lightly active (×1.375): light exercise 1–3 days/week
• Moderately active (×1.55): exercise 3–5 days/week
• Very active (×1.725): hard exercise 6–7 days/week
• Extra active (×1.9): physical job + intense training

From TDEE to a weight goal

The classic conversion: 1 kg of body fat ≈ 7,700 kcal (≈ 3,500 kcal per pound). To lose 0.5 kg per week, you need a daily deficit of (0.5 × 7700) ÷ 7 ≈ 550 kcal. To gain 0.5 kg per week, the same surplus.

Real life is messier: water weight, glycogen, sodium, and thermogenic adaptation all bend the curve. But the calories-in/calories-out arithmetic is the right starting point for any plan.

Sustainable rates of change

Faster isn't better. For sustained, fat-preferring weight loss, target 0.5–1% of body weight per week. A 90 kg person should lose roughly 0.45–0.9 kg/week. Aggressive deficits below ~80% of TDEE risk muscle loss, hormonal disruption, and metabolic slowdown.

For lean gain (“bulking”), the same caution applies in reverse. Around +250–500 kcal/day is plenty for most lifters; surpluses much larger than that mostly buy fat, not muscle.

The 30 / 40 / 30 macro split

This calculator uses a balanced default split of 30% protein, 40% carbohydrates, 30% fat — appropriate for general fitness. Convert calories to grams using the standard energy densities: protein 4 kcal/g, carbs 4 kcal/g, fat 9 kcal/g. Higher protein splits (35–40%) are common during a cut to preserve lean mass; lower protein (~20%) is fine for recreational athletes at maintenance.

Worked example

A 30-year-old male, 180 cm, 80 kg, exercising 3–5 days a week. Mifflin-St Jeor gives:

For a half-kilo-per-week cut, target ~2,209 kcal/day. For a half-kilo bulk, ~3,309 kcal/day.

Disclaimer

These numbers are educated estimates. Individual metabolic rates can vary ±10–15% from any predictive equation. Track your weight trend over 2–4 weeks and adjust intake by 100–200 kcal/day if it's drifting in the wrong direction. For medical or clinical guidance, consult a registered dietitian or physician.