A calorie deficit is the foundation of fat loss. When you consume fewer calories than your body burns, it draws on stored fat for energy. Understanding how to calculate and maintain the right deficit makes weight loss predictable rather than guesswork.
What Is a Calorie Deficit?
Calorie deficit = Calories burned (TDEE) − Calories consumed
A deficit of 500 calories per day theoretically produces about 0.5 kg (1 lb) of fat loss per week, since roughly 7,700 calories = 1 kg of body fat.
Step 1: Calculate Your TDEE
Your Total Daily Energy Expenditure (TDEE) is the total calories your body burns in a day.
Step 1a — Find your BMR (Basal Metabolic Rate) using Mifflin-St Jeor:
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
Step 1b — Multiply by activity level:
| Activity level | Multiplier |
|---|---|
| Sedentary (desk job, no exercise) | × 1.2 |
| Lightly active (1–3 days/week) | × 1.375 |
| Moderately active (3–5 days/week) | × 1.55 |
| Very active (6–7 days/week) | × 1.725 |
| Extremely active (physical job + training) | × 1.9 |
Example: 30-year-old woman, 65 kg, 165 cm, moderately active:
BMR = (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 1,401
TDEE = 1,401 × 1.55 = 2,172 calories/day
Step 2: Choose Your Deficit
| Goal | Daily deficit | Weekly loss |
|---|---|---|
| Gentle / sustainable | 250 kcal | ~0.25 kg |
| Standard | 500 kcal | ~0.5 kg |
| Aggressive | 750 kcal | ~0.75 kg |
| Maximum recommended | 1,000 kcal | ~1 kg |
A deficit above 1,000 kcal/day risks muscle loss, nutritional deficiencies, and metabolic adaptation.
Step 3: Set Your Calorie Target
Daily calorie target = TDEE − Deficit
From the example above: 2,172 − 500 = 1,672 calories/day
The Plateau Problem
After several weeks, weight loss often stalls. Reasons:
- Metabolic adaptation — your body becomes more efficient
- Less body weight = lower TDEE (you've lost mass)
- Calorie tracking errors — portions creep up
Fix: Recalculate TDEE with your new weight every 4–6 weeks.
Protein Target During a Deficit
Eating sufficient protein preserves muscle mass while losing fat. Target:
1.6–2.2 g of protein per kg of bodyweight
For a 65 kg person: 104–143 g protein per day.
Practical Tips
- Weigh yourself weekly (not daily) and average across a week
- High-volume, low-calorie foods (vegetables, lean protein) reduce hunger
- A deficit works best combined with resistance training to retain muscle
- Sleep deprivation increases hunger hormones — prioritise 7–9 hours