Losing weight comes down to one principle: consume fewer calories than you burn. But knowing exactly how much less to eat, and how long it will take to reach your goal, requires precise calculation.
This calculator uses your TDEE (Total Daily Energy Expenditure) — calculated from the Mifflin-St Jeor equation — combined with your goal weight and preferred loss rate to give you a personalised calorie target, weekly fat loss projection, and realistic timeline.
How the Weight Loss Calculator Works
The calculator first computes your TDEE (Total Daily Energy Expenditure) using the Mifflin-St Jeor equation — the most validated BMR formula for modern populations. Your chosen deficit is subtracted from your TDEE to give your daily calorie target. The timeline is calculated from the energy equivalent of body fat: 1 kg of fat ≈ 7,700 kcal.
What is a Safe Calorie Deficit?
Research supports deficits of 250–750 kcal/day for most people. The 500 kcal/day deficit (yielding ~0.45 kg/week) is the most widely recommended rate — large enough for meaningful progress, small enough to preserve muscle mass, energy, and hormonal health. Deficits above 1,000 kcal/day significantly increase muscle loss and nutritional risk.
Why Does Weight Loss Slow Over Time?
As you lose weight, your TDEE decreases — your body requires fewer calories to maintain a lighter frame. Additionally, adaptive thermogenesis (metabolic adaptation) can reduce your TDEE by 100–300 kcal after several weeks in a deficit. This is why recalculating every 5–10 kg lost, and taking occasional diet breaks, is essential for long-term success.
The Role of Protein in Fat Loss
High protein intake (1.8–2.2 g/kg) during a calorie deficit is the single most important nutritional strategy for preserving lean muscle mass while losing fat. Protein also has the highest thermic effect of food (20–30% of calories burned in digestion), increases satiety, and stabilises blood sugar. Prioritise protein even when overall calories are reduced.
Exercise During Weight Loss
Exercise creates additional calorie expenditure and helps preserve muscle during a deficit. Resistance training 3× per week is more effective than cardio alone for maintaining body composition during fat loss. Avoid dramatically increasing exercise volume simultaneously with cutting calories — the combined stress can impair recovery and adherence.
💡 Expert Tips
- ✓Weigh yourself at the same time each day (morning, fasted). Use the weekly average, not daily readings, to track true progress.
- ✓Protein should be ≥1.8 g/kg during fat loss — it prevents muscle loss and keeps you full longer.
- ✓Take a 1–2 week diet break (eating at TDEE) every 8–12 weeks to restore leptin levels and prevent metabolic adaptation.
- ✓Strength train 3× per week — muscle preservation during fat loss dramatically improves body composition outcomes.
- ✓Recalculate your TDEE every time you lose 5–10 kg, as your calorie needs decrease as you get lighter.
📊 Deficit Rate vs Weekly Fat Loss
| Daily Deficit | Weekly Loss | Monthly Loss | Safety Rating |
|---|---|---|---|
| −250 kcal | ~0.23 kg | ~1 kg | Very safe |
| −500 kcal | ~0.45 kg | ~2 kg | Recommended |
| −750 kcal | ~0.68 kg | ~3 kg | Moderate risk |
| −1,000 kcal | ~0.91 kg | ~4 kg | Maximum safe |
| −1,200+ kcal | 1.1+ kg | 4.8+ kg | ⚠ Risky — GP advice |
Frequently Asked Questions
How many calories should I cut to lose 0.5 kg per week?+
Is 1 kg per week weight loss safe?+
Why does weight loss plateau after a few weeks?+
Should I eat back exercise calories?+
What is the minimum calories I should eat to lose weight?+
How long does it take to lose 10 kg?+
Related Calculators
Calorie Deficit Calculator
Calculate your daily calorie deficit to lose weight at a safe, sustainable rate without sacrificing muscle.
TDEE Calculator
Calculate your Total Daily Energy Expenditure. The most important number for setting any nutrition goal.
Macro Calculator
Calculate your optimal protein, carbohydrate, and fat targets based on your calorie goal and fitness objective.