How the Weight Loss Calculator works
This calculator uses the widely accepted 7,700 kcal per kilogram of fat rule (3,500 kcal per pound). To lose 1 kg of body fat, you need to create a cumulative calorie deficit of 7,700 kcal.
Days to goal = (kg to lose × 7,700) ÷ daily calorie deficit
Weeks to goal = Days ÷ 7
Example
You weigh 80 kg and want to reach 70 kg with a 500 kcal/day deficit:
10 kg × 7,700 = 77,000 kcal total deficit needed
77,000 ÷ 500 = 154 days = 22 weeks ≈ 5.1 months
Safe rate of weight loss
- 0.25–0.5 kg/week — slow and sustainable, minimal muscle loss
- 0.5–1.0 kg/week — recommended for most people (500 kcal deficit)
- 1.0+ kg/week — aggressive, risk of muscle loss and nutrient deficiencies
How to use your results
Once you have your timeline, the key is creating the right calorie deficit. Use the TDEE Calculator to find your maintenance calories, then subtract your chosen deficit to get your daily calorie target.
Track your intake using a food diary or app. Weigh yourself once per week, in the morning, under the same conditions. Adjust your deficit if progress stalls for 2+ weeks.
Combine calorie restriction with strength training to preserve muscle mass during weight loss — this is the single most effective way to improve body composition rather than just losing weight.
Frequently asked questions
How long does it take to lose 10 kg?
With a 500 kcal/day deficit, losing 10 kg takes approximately 22 weeks (5.5 months). With a 1,000 kcal/day deficit, it takes about 11 weeks. The 500 kcal deficit is recommended as it preserves more muscle mass.
How many calories do I need to cut to lose 1 kg per week?
To lose 1 kg per week you need a deficit of 7,700 kcal per week, which means 1,100 kcal per day. Most guidelines recommend a maximum deficit of 1,000 kcal/day to avoid muscle loss and nutrient deficiencies.
Is losing 0.5 kg per week healthy?
Yes — 0.5 kg per week is generally considered a safe, sustainable rate of weight loss. It requires a 500 kcal/day deficit and minimises muscle loss compared to faster rates.
Why am I not losing weight despite a calorie deficit?
Common reasons include: underestimating calorie intake (cooking oils, sauces, drinks), overestimating exercise calories burned, water retention masking fat loss, or metabolic adaptation after extended dieting. Track accurately for 2 weeks and reassess.
How accurate is the 7,700 kcal per kg rule?
The 7,700 kcal/kg rule is a good estimate but not exact. Individual metabolism, body composition, and hormonal factors affect actual fat loss rates. Real-world results typically range from 6,000 to 9,000 kcal per kg of fat lost.
What is a realistic weight loss goal?
Most health authorities (WHO, NHS) recommend losing 0.5–1 kg per week as realistic and sustainable. Losing faster is possible but increases the risk of muscle loss, gallstones, and nutrient deficiencies.
Should I use a 500 or 1000 kcal deficit?
A 500 kcal/day deficit is optimal for most people — it produces approximately 0.5 kg/week of fat loss while preserving muscle. A 1,000 kcal deficit is appropriate for people with obesity under medical supervision.
How do I maintain weight loss long-term?
The most successful strategies are: gradual weight loss (not crash dieting), building sustainable eating habits, regular physical activity (especially resistance training), adequate protein intake (1.6–2g/kg), and monitoring weight weekly with small adjustments.
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