A calorie deficit is the only proven mechanism for weight loss. Everything else — low carb, intermittent fasting, detox teas, fat burners — works only insofar as it helps you eat fewer calories than you burn.
Understanding calorie deficits properly helps you lose weight at a sensible rate, preserve muscle, and avoid the metabolic slowdown that derails most diets.
What Is a Calorie Deficit?
A calorie deficit occurs when you consume fewer calories than your body burns in a given day. Your body needs to make up the energy shortfall from somewhere — and it draws on stored body fat to do so.
The relationship is straightforward:
- 3,500 calories ≈ 1 pound (0.45kg) of body fat
- A 500 calorie daily deficit → approximately 1 pound of fat loss per week
- A 250 calorie daily deficit → approximately 0.5 pounds per week
These numbers aren't perfectly precise for every individual — metabolism varies, hormones play a role, and water retention can mask fat loss on the scale — but they're reliable enough as a planning framework.
Step 1: Calculate Your TDEE
Your Total Daily Energy Expenditure (TDEE) is the number of calories your body burns per day, accounting for your activity level. This is the number you build your deficit from.
TDEE = BMR × Activity Multiplier
BMR (Basal Metabolic Rate) — calories burned at complete rest:
- Mifflin-St Jeor equation (most accurate):
- Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5 - Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161
Activity multipliers:
| Activity Level | Multiplier |
|---|---|
| Sedentary (desk job, little exercise) | 1.2 |
| Lightly active (light exercise 1–3 days/week) | 1.375 |
| Moderately active (moderate exercise 3–5 days/week) | 1.55 |
| Very active (hard exercise 6–7 days/week) | 1.725 |
| Extremely active (physical job + daily training) | 1.9 |
Example:
- 30-year-old woman, 70kg, 165cm, lightly active
- BMR = (10 × 70) + (6.25 × 165) − (5 × 30) − 161 = 700 + 1,031 − 150 − 161 = 1,420 BMR
- TDEE = 1,420 × 1.375 = 1,953 calories/day
Step 2: Set Your Calorie Target
Once you know your TDEE, subtract your deficit:
| Goal | Daily Deficit | Weekly Loss (approx.) |
|---|---|---|
| Conservative (low muscle loss risk) | 250 calories | 0.25kg / 0.5 lbs |
| Standard | 500 calories | 0.5kg / 1 lb |
| Aggressive | 750 calories | 0.75kg / 1.5 lbs |
| Very aggressive (not recommended) | 1,000+ calories | 1kg+ / 2 lbs+ |
For most people, a 500-calorie deficit is the sweet spot. You lose roughly half a kilogram per week — fast enough to see results, slow enough to preserve muscle and maintain energy.
Do not go below 1,200 calories (women) or 1,500 calories (men), regardless of your calculated deficit. Below these thresholds, it becomes very difficult to meet your protein and micronutrient needs.
From the example above:
- TDEE: 1,953 calories
- 500-calorie deficit → target: 1,453 calories/day
Step 3: Set Your Protein Target
Protein is the most important macro when losing weight. It:
- Preserves muscle mass during a deficit (essential — you want to lose fat, not muscle)
- Is the most satiating macro (reduces hunger significantly)
- Has the highest thermic effect (your body burns ~25% of protein calories just digesting it)
Protein target during a deficit:
- 0.7–1g of protein per pound of bodyweight (1.5–2.2g per kg)
- For a 70kg person: aim for 110–154g protein per day
Hit your protein target first. Then fill remaining calories with carbohydrates and fat in whatever ratio you prefer.
Step 4: Track Your Intake
You cannot estimate a calorie deficit reliably — you have to track it. Research consistently shows that people underestimate their calorie intake by 20–40%, which is enough to completely eliminate a deficit without realising it.
Use a calorie tracking app:
NutriBalance is the best free option for Android. Log every meal — breakfast, lunch, dinner, snacks, cooking oils, drinks. The barcode scanner and AI food label scanner make logging fast enough to actually sustain.
Critical logging rules:
- Weigh food on a digital scale — don't estimate portion sizes
- Log cooking oils and condiments (often 200–400 hidden calories)
- Log the raw weight of meat before cooking
- Log drinks — fruit juice, lattes, protein shakes, alcohol all count
Step 5: Weigh Yourself Consistently
The scale doesn't move linearly. Hormonal fluctuations, water retention, bowel contents, and glycogen stores can all shift your weight by 1–2kg from day to day without any change in actual body fat.
Weigh yourself consistently:
- Same time every day (first thing in the morning, after using the bathroom)
- Record it in your app (NutriBalance has a built-in weight tracker)
- Look at your 7-day average — not day-to-day changes
If your 7-day average is trending down by roughly your expected rate, the plan is working. If it's flat for 3+ weeks, your calorie intake needs adjustment.
When to Adjust Your Deficit
Your deficit should change as you lose weight. As your body gets lighter, it burns fewer calories. A 500-calorie deficit at 90kg becomes a smaller deficit at 75kg — because your TDEE has decreased.
Recalculate your TDEE every 5–10kg of weight lost and adjust your calorie target accordingly.
If fat loss stalls:
- First, audit your tracking — are you logging everything accurately? Cooking oils and condiments are the most common hidden sources.
- Reduce calories by 100–150 per day (not a drastic cut).
- Consider a 1–2 week diet break at maintenance — this can help reset hormones and reduce diet fatigue before resuming the deficit.
Common Calorie Deficit Mistakes
Mistake 1: Starting too aggressively A 1,000+ calorie deficit feels faster but increases muscle loss, causes extreme hunger, and is unsustainable. Losing 0.5–1kg per week is far better for body composition and long-term success.
Mistake 2: "Eating back" all exercise calories Apps and fitness trackers notoriously overestimate calories burned during exercise. If you burned 400 calories on a run, eating back 400 calories often eliminates your deficit. Add exercise calories conservatively — at most 50%.
Mistake 3: Ignoring protein People in a calorie deficit who don't eat enough protein lose significant amounts of muscle alongside fat. Muscle loss slows your metabolism and worsens body composition. Hit your protein target every day.
Mistake 4: The "weekend effect" A perfect 500-calorie deficit Monday–Friday followed by 1,000+ calorie surpluses Saturday and Sunday can eliminate an entire week of progress. Track on weekends — this is where most deficits fall apart.
How Fast Should You Lose Weight?
Evidence-based rates:
- 0.5–1% of bodyweight per week is generally considered optimal for fat loss while preserving muscle
- For a 90kg person: 450g–900g per week
- For a 70kg person: 350g–700g per week
Faster than this increases muscle loss risk. Slower is fine if sustainable — consistency beats speed.
Frequently Asked Questions
How big should my calorie deficit be? For most people, 300–500 calories below your TDEE is optimal. This produces 0.3–0.5kg of fat loss per week while minimising muscle loss and hunger.
Do I have to count calories to lose weight? Technically no, but research consistently shows that people who track their intake lose significantly more weight than those who don't. Tracking apps make this process quick — under 10 minutes per day with a barcode scanner.
What is the fastest way to lose weight in a calorie deficit? Maximise protein intake (preserves muscle), minimise liquid calories (low satiety per calorie), prioritise high-volume low-calorie foods like vegetables, and add resistance training (preserves muscle and increases TDEE).
Will I lose muscle in a calorie deficit? Some muscle loss is possible, but it's minimised by: eating adequate protein (0.8–1g per pound of bodyweight), continuing resistance training during the deficit, and not creating too aggressive a calorie restriction (stay above a 750-calorie deficit).
What app should I use to track a calorie deficit? NutriBalance is the best free calorie tracking app for Android. Set your custom calorie goal, track your intake with the barcode or AI scanner, and monitor your weight trend over time in the built-in weight tracker.
Track your calories, macros, and streaks for free with NutriBalance — the gamified calorie tracker for Android.
