How to Calculate a Calorie Deficit for Fat Loss (Step-by-Step)
A calorie deficit means consuming fewer calories than your body burns. This forces your body to burn stored fat for energy. The science is simple. The execution requires knowing your numbers.
What Is a Calorie Deficit?
A calorie deficit occurs when you eat fewer calories than your body burns in a day. Your body then draws on stored fat (and potentially muscle) to make up the energy shortfall. One pound (0.45kg) of fat contains approximately 3,500 calories — so a daily deficit of 500 calories produces roughly 0.45kg of fat loss per week.
How Many Calories Should You Cut?
| Deficit | Daily Cut | Weekly Loss | Risk Level |
|---|---|---|---|
| Mild | 250 kcal | ~0.25 kg | Very Low |
| Moderate ✓ | 500 kcal | ~0.5 kg | Low |
| Aggressive | 750 kcal | ~0.75 kg | Moderate |
| Maximum | 1,000 kcal | ~1 kg | High |
The 500 calorie daily deficit is the sweet spot for most people: meaningful fat loss of approximately 2kg per month, minimal muscle loss when combined with adequate protein, and sustainable long-term.
Step-by-Step Example
Person: 30-year-old male, 175cm, 85kg, moderately active.
Step 1 — Calculate BMR: (10 × 85) + (6.25 × 175) − (5 × 30) + 5 = 850 + 1,094 − 150 + 5 = 1,799 kcal
Step 2 — Calculate TDEE: 1,799 × 1.55 = 2,789 kcal/day
Step 3 — Set deficit: 2,789 − 500 = 2,289 kcal/day fat loss target
Expected result: 0.5kg fat loss per week = 2kg per month.
The 5 Biggest Mistakes
1. Underestimating food intake. Studies consistently show people underestimate calories by 20–50%. Weigh food on a kitchen scale for at least the first 2 weeks.
2. Going too aggressive. Cutting more than 750–1,000 cal/day accelerates muscle loss and triggers metabolic adaptation that makes subsequent fat loss harder.
3. Not eating enough protein. Without adequate protein (1.8–2.4g/kg), up to 40% of weight lost can be lean mass rather than fat.
4. Not adjusting as you lose weight. As you get lighter, your TDEE decreases. Recalculate every 4–6 weeks and adjust your calorie target.
5. No resistance training. Exercise, specifically lifting weights, is the most powerful tool for preserving lean muscle during a deficit.
Frequently Asked Questions
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References
- Hall KD et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011.
- Stiegler P & Cunliffe A. The role of diet and exercise for fat-free mass maintenance. Sports Medicine, 2006.