How This Calculation Works
This calculator first finds your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest just to keep essential functions running — using the Mifflin-St Jeor equation, which is widely regarded as one of the more accurate formulas for the general population. It uses your weight, height, age, and sex.
BMR alone doesn't account for daily movement, exercise, or activity, so the calculator multiplies it by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active) to estimate your Total Daily Energy Expenditure (TDEE) — the total calories you burn in an average day, including everything from walking to workouts.
TDEE represents your maintenance calories — eating this amount should keep your weight roughly stable. To lose weight, you eat below TDEE (a calorie deficit); to gain weight, you eat above it (a calorie surplus). A deficit or surplus of about 500 calories per day roughly corresponds to 0.5 kg (about 1 lb) of weight change per week, since one kilogram of body fat contains approximately 7,700 calories.
Common Mistakes to Avoid
- Choosing the wrong activity level. Most people overestimate their activity level. "Moderate" assumes structured exercise 3-5 days a week — if your job is mostly sitting and you don't exercise regularly, "Sedentary" or "Light" is usually more accurate.
- Expecting the numbers to be exact. These formulas are population averages with a margin of error of roughly ±10%. Use the result as a starting point, then adjust based on how your actual weight changes over 2-3 weeks.
- Cutting calories too aggressively. A deficit larger than about 500-750 calories/day often leads to muscle loss, fatigue, and metabolic slowdown. Slow, sustainable deficits produce better long-term results than crash diets.
- Not recalculating as your weight changes. Your calorie needs change as your weight changes — recalculate every 5-10 kg (10-20 lb) of weight change, or every few months, to keep your targets accurate.
Worked Example
Scenario: A 30-year-old male, 175 cm tall, 75 kg, moderately active (exercise 3-5 days/week).
Step 1 — BMR (Mifflin-St Jeor): 10 × 75 + 6.25 × 175 − 5 × 30 + 5 = 750 + 1,093.75 − 150 + 5 = 1,698.75, rounded to 1,699 cal/day.
Step 2 — Apply activity multiplier: 1,699 × 1.55 (moderate) ≈ 2,633 cal/day. This is his TDEE.
Step 3 — Set a goal: To lose about 0.5 kg/week, he'd eat roughly 2,633 − 500 = 2,133 calories/day.