How to Calculate Your Calorie Deficit (And Actually Stick to It)
Learn the exact science behind calorie deficits — how to calculate your TDEE, set a sustainable target, and avoid the common mistakes that stall fat loss.
Why Most Diets Fail Before They Start
Most people approach fat loss backwards. They pick a random calorie number — usually something extreme like 1,200 calories — and wonder why they feel exhausted, hungry, and eventually quit. The problem isn't willpower. It's math.
Fat loss is governed by one simple principle: you must consume fewer calories than your body burns. But "fewer" doesn't mean "as few as possible." It means the right deficit for your body, your goals, and your lifestyle.
Step 1: Calculate Your Basal Metabolic Rate (BMR)
Your BMR is the number of calories your body burns at complete rest — just to keep your organs functioning. The most accurate formula for most people is the Mifflin-St Jeor equation:
For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Example: A 30-year-old woman who weighs 70 kg and is 165 cm tall has a BMR of approximately 1,491 calories per day.
Step 2: Calculate Your Total Daily Energy Expenditure (TDEE)
Your BMR only accounts for rest. Your TDEE adds the calories burned through daily activity:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, little to no exercise |
| Lightly Active | × 1.375 | Light exercise 1–3 days/week |
| Moderately Active | × 1.55 | Moderate exercise 3–5 days/week |
| Very Active | × 1.725 | Hard exercise 6–7 days/week |
| Extremely Active | × 1.9 | Physical job + hard training |
Using the example above with a lightly active lifestyle: TDEE = 1,491 × 1.375 = 2,050 calories/day.
Step 3: Set Your Deficit
A 500-calorie daily deficit produces approximately 0.45 kg (1 lb) of fat loss per week. This is the sweet spot recommended by most nutrition researchers because it:
- Preserves lean muscle mass
- Keeps hunger manageable
- Is sustainable for months, not days
Avoid deficits larger than 1,000 calories/day. Extreme restriction triggers metabolic adaptation — your body slows its metabolism to compensate, making fat loss progressively harder.
| Weekly Goal | Daily Deficit | Notes |
|---|---|---|
| 0.25 kg / 0.5 lb | −250 cal | Ideal for athletes preserving muscle |
| 0.45 kg / 1 lb | −500 cal | Best for most people |
| 0.9 kg / 2 lb | −1,000 cal | Maximum safe rate; only short-term |
Step 4: Track Macros, Not Just Calories
Hitting your calorie target is necessary, but your macro split determines whether you lose fat or muscle. A proven starting point:
- Protein: 1.6–2.2 g per kg of body weight (the most important macro for preserving muscle)
- Carbohydrates: 40–50% of remaining calories (fuel for workouts and brain function)
- Fats: 25–35% of remaining calories (hormones, satiety, nutrient absorption)
For our 70 kg example at 1,550 calories target: aim for 112–154 g protein, then split the remaining calories between carbs and fats based on preference.
The 3 Most Common Mistakes
1. Eating back exercise calories. Fitness trackers dramatically overestimate burn. If you exercise, choose the appropriate activity multiplier in your TDEE calculation — don't add extra food on top.
2. Ignoring liquid calories. A single latte, juice, or sports drink can add 150–300 calories invisibly. Track everything for the first two weeks to build awareness.
3. Cutting too fast, then bingeing. A 1,500-calorie deficit feels manageable for three days and unbearable by day four. A 500-calorie deficit feels easy every single day. Slow and steady wins every time.
When to Adjust Your Deficit
Your TDEE changes as you lose weight. Every 4–6 weeks, recalculate using your new weight. If fat loss stalls for two consecutive weeks despite tracking accurately, reduce calories by 100–150 per day rather than making a dramatic cut.
The Bottom Line
Sustainable fat loss is a precision exercise, not a punishment. Calculate your TDEE, apply a moderate deficit, hit your protein target, and give it 8–12 weeks before judging results. The math always works — the only variable is consistency.
Use our free Calorie Deficit Calculator to get your personalised numbers in 60 seconds.