How Your Calorie Target Is Calculated
This calculator first estimates your BMR (Mifflin-St Jeor equation), multiplies it by an activity factor to get your TDEE (maintenance calories), then applies an adjustment based on your goal:
- Moderate weight loss: −500 calories/day (roughly 1 lb / 0.45 kg loss per week)
- Mild weight loss: −250 calories/day (roughly 0.5 lb / 0.25 kg loss per week)
- Mild weight gain: +250 calories/day
- Moderate weight gain: +500 calories/day
Why 500 Calories ≈ 1 Pound Per Week
One pound of body fat contains roughly 3,500 calories of stored energy. A daily deficit or surplus of 500 calories, sustained over 7 days, totals approximately 3,500 calories — hence the widely used "500 calories/day ≈ 1 lb/week" rule of thumb, though real-world results vary due to metabolic adaptation and other individual factors.
Sustainable Rates of Change
Moderate, sustainable deficits/surpluses (0.5-1 lb per week) are generally easier to maintain long-term and better preserve muscle mass (during loss) or minimize fat gain (during bulking) compared to more aggressive, faster targets.