How to Calculate a Safe Rate of Weight Loss
Understanding the math behind weight loss helps you set realistic goals and avoid the metabolic damage that comes from cutting calories too aggressively. The core principle is creating a consistent calorie deficit over time.
The Fundamental Formula
1 pound of fat ≈ 3,500 calories
Weekly loss of 1 lb → Deficit of 500 cal/day
Weekly loss of 2 lb → Deficit of 1,000 cal/day
Step-by-Step Calculation
Starting point: Calculate your Total Daily Energy Expenditure (TDEE).
Using the Mifflin-St Jeor equation:
- Men: TDEE = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: TDEE = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Then multiply by activity factor:
- Sedentary: × 1.2
- Lightly active: × 1.375
- Moderately active: × 1.55
- Very active: × 1.725
Example: 35-year-old woman, 75 kg, 165 cm, moderately active. BMR = (10 × 75) + (6.25 × 165) − (5 × 35) − 161 = 1,476 kcal TDEE = 1,476 × 1.55 = 2,288 kcal/day
To lose 1 lb/week: Eat 2,288 − 500 = 1,788 kcal/day
Why You Shouldn't Cut More Than 1,000 Cal/Day
- Muscle loss accelerates below aggressive deficits
- Metabolic rate adapts (decreases) more significantly
- Nutrient deficiencies become harder to avoid
- Hunger becomes unsustainable, leading to rebound
Timeline Calculation
Time to Goal = (Current weight − Goal weight) × 3,500 / Daily deficit
75 kg → 65 kg (22 lb loss) at 500 cal/day deficit: 22 × 3,500 / 500 = 154 days ≈ 5 months
Use our weight loss calculator to plan your calorie target and timeline.