How the Weight Loss Calculator Works
This calculator uses the Mifflin-St Jeor equation — the most accurate formula for estimating Basal Metabolic Rate (BMR) available. It was validated in a 2005 meta-analysis by the Academy of Nutrition and Dietetics as the preferred method for estimating resting energy expenditure.
Step 1: Calculate Your BMR
BMR is the number of calories your body burns at complete rest — just to keep your heart beating, lungs breathing, and organs functioning. The Mifflin-St Jeor formula is:
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Step 2: Apply Your Activity Multiplier (TDEE)
Your Total Daily Energy Expenditure (TDEE) accounts for how active you are. We multiply your BMR by an activity factor:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, little or no exercise |
| Lightly Active | × 1.375 | Light exercise 1–3 days/week |
| Moderately Active | × 1.55 | Moderate exercise 3–5 days/week |
| Very Active | × 1.725 | Hard exercise 6–7 days/week |
| Extra Active | × 1.9 | Physical job + twice-daily training |
Step 3: Create Your Calorie Deficit
One kilogram of body fat contains approximately 7,700 kcal of stored energy. To lose 0.5 kg per week, you need a deficit of ~3,850 kcal per week — or 550 kcal per day. We subtract this from your TDEE to get your daily calorie target.
How Fast Should You Lose Weight?
Research consistently shows that losing 0.5–1% of your body weight per week is both safe and sustainable. Faster rates often cause muscle loss, nutritional deficiencies, and metabolic adaptation — making the weight much harder to keep off long-term.
- 0.25 kg/week — Very gentle, best for those close to goal or with very active lifestyles
- 0.5 kg/week — The sweet spot recommended by most dietitians and health organisations
- 0.75–1 kg/week — Appropriate for those with significant weight to lose, but requires careful nutrition planning
Understanding Your Macros
Calories matter most for weight loss, but macronutrient ratios affect body composition, hunger, and performance. This calculator uses an evidence-based split:
- Protein (30%): Essential for preserving muscle during a calorie deficit. Target ~1.6–2.2 g per kg of body weight.
- Carbohydrates (40%): Primary fuel for the brain and exercise. Choose whole grains, vegetables, and fruit.
- Fat (30%): Critical for hormone production and fat-soluble vitamin absorption.
