What Is a Calorie Deficit?
A calorie deficit means eating fewer calories than your body burns each day (your TDEE). When you consume fewer calories than you expend, your body makes up the difference by breaking down stored fat for energy — resulting in weight loss. A 500-calorie daily deficit typically leads to about 0.5 kg (1 lb) of fat loss per week. Your deficit should be large enough to produce results but not so large that it triggers metabolic adaptation, muscle loss, or nutrient deficiencies.
How to Use This Calculator
- Enter your stats — Gender, age, height, current weight, and goal weight.
- Choose your activity level — Be honest. Overestimating activity leads to underestimating your deficit.
- Select deficit size — 500 cal/day is the recommended sweet spot for most people.
- Click calculate — Your daily calorie target, weekly loss rate, and time to goal will appear.
- Check your BMR — Never eat below your BMR without medical supervision. The calculator warns you in red if your target is too low.
Safe Deficit Guide
| Deficit | Weekly Loss | Best For |
|---|---|---|
| 250 cal | ~0.25 kg (0.5 lb) | Slow, easy maintenance. Minimal hunger. |
| 500 cal | ~0.5 kg (1 lb) | Most people. Sustainable, good results. |
| 750 cal | ~0.75 kg (1.5 lb) | Faster results. Higher protein needed to preserve muscle. |
| 1000 cal | ~1 kg (2 lb) | Short-term only. Risk of muscle loss and metabolic slowdown. |
Tips for Success
- Prioritize protein — 1.6-2.2 g per kg of body weight preserves muscle during a deficit.
- Don't cut too much — Extreme deficits slow metabolism and cause muscle loss. Losing more than 1 kg per week is rarely sustainable.
- Exercise helps maintenance — Strength training preserves muscle. Cardio increases the deficit without cutting more food.
- Plateaus are normal — As you lose weight, your TDEE decreases. Recalculate every 5 kg lost.
Metabolic Adaptation: Why Diets Stop Working
When you lose weight, your metabolism slows down — metabolic adaptation. Studies show it can be 10-20% greater than expected from weight loss alone. A 500-calorie deficit at 90 kg may be only a 300-calorie deficit at 75 kg. Recalculate your TDEE every 5 kg lost.
How to Overcome a Plateau
- Recalculate TDEE — Maintenance decreases as you lose weight.
- Increase activity — More steps, harder workouts.
- Check tracking accuracy — Hidden calories from sauces, oils, drinks add up.
- Take a diet break — Eat at maintenance for 1-2 weeks, then resume deficit.
- Increase protein — 2.0-2.4 g/kg increases satiety and thermic effect.
The Danger of Crash Diets
Very low-calorie diets (under 800-1000 cal/day) may produce rapid weight loss, but up to 40% can be muscle. Muscle loss lowers BMR and makes long-term maintenance harder. Crash dieters often regain more weight than they lost within 1-2 years.
Weight Loss vs Fat Loss
The scale measures total weight — fat, muscle, water, bone. Body composition tells you whether you’re losing fat or muscle. Aim for fat loss, not just weight loss. Preserving muscle helps you maintain results long term.
Frequently Asked Questions
How much of a calorie deficit for weight loss?
300-500 calories below TDEE is safe and sustainable. This yields 0.5-1 kg (1-2 lbs) per week. Larger deficits increase muscle loss risk.
What happens if I eat too little?
Eating below your BMR triggers metabolic adaptation — your body slows calorie burning, conserves energy, and may break down muscle. This is why crash diets fail long-term.
Do I need to exercise in a deficit?
Not strictly — you can lose weight with diet alone. However, strength training prevents muscle loss, and cardio increases the deficit allowing you to eat more while still losing weight.
Sources: National Institutes of Health (NIH), Academy of Nutrition and Dietetics, Journal of the International Society of Sports Nutrition.