Weight loss comes down to one fundamental principle: burn more calories than you consume. This is called a calorie deficit, and it's the most scientifically validated method for losing fat.
Everything else — keto, intermittent fasting, HIIT, paleo — works because it helps people eat fewer calories. The diet itself doesn't matter as much as the deficit it creates.
This guide explains exactly how to calculate the right deficit for your body, how fast you can expect to lose weight, and the most common mistakes that stall progress.
Calculate your personal calorie deficit → | Find your TDEE →
What Is a Calorie Deficit?
A calorie deficit occurs when you consume fewer calories than your body burns in a day.
Your body always needs energy to function — for breathing, heart function, digestion, body temperature, and movement. This total daily energy requirement is your TDEE (Total Daily Energy Expenditure).
If you eat less than your TDEE, your body draws on stored energy (primarily fat) to make up the difference. This is weight loss.
The math:
- 1 kg of fat ≈ 7,700 calories
- A daily deficit of 500 calories = ~3,500 calories/week = ~0.45 kg of fat loss per week
- A daily deficit of 1,000 calories = ~7,000 calories/week = ~0.9 kg of fat loss per week
Step 1: Calculate Your BMR
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — just to keep you alive.
The most accurate formula for most people is the Mifflin-St Jeor equation, validated by the American Dietetic Association:
For men: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) + 5
For women: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) − 161
Example (Male, 30 years, 80 kg, 175 cm): BMR = (10 × 80) + (6.25 × 175) − (5 × 30) + 5 BMR = 800 + 1093.75 − 150 + 5 = 1,748.75 calories/day
This is how many calories you'd burn lying in bed doing nothing all day.
Step 2: Calculate Your TDEE
TDEE accounts for your actual daily activity. Multiply your BMR by your activity factor:
| Activity Level | Description | 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 |
| Extra Active | Physical job + hard training | 1.9 |
Continuing the example (Moderately Active): TDEE = 1,748.75 × 1.55 = 2,711 calories/day
This means at 2,711 calories/day, this person's weight stays the same. Eat less → lose weight. Eat more → gain weight.
Get your exact TDEE in seconds →
Step 3: Choose Your Deficit Size
| Goal | Daily Deficit | Weekly Loss | Best For |
|---|---|---|---|
| Slow, sustainable | 250–300 cal | ~0.2–0.25 kg | Beginners, minimal muscle loss |
| Standard | 500 cal | ~0.45 kg | Most people |
| Aggressive | 750–1,000 cal | ~0.7–0.9 kg | Faster results, higher muscle loss risk |
The sweet spot for most people is a 500-calorie daily deficit — resulting in roughly 0.5 kg per week.
Do not go below 1,200 calories/day (women) or 1,500 calories/day (men) without medical supervision. Extreme restriction causes muscle loss, nutrient deficiencies, and metabolic adaptation.
Continuing the example: TDEE: 2,711 cal Target (500 deficit): 2,711 − 500 = 2,211 calories/day Expected loss: ~0.45 kg/week
Calculate your exact calorie target →
What to Eat: Protein Is the Priority
Total calories determine whether you lose weight. What you eat determines whether you lose fat or muscle.
The most important macronutrient for fat loss is protein.
Why protein matters during a deficit:
- Preserves muscle mass while you lose fat
- Higher thermic effect — you burn ~25–30% of protein calories just digesting it
- The most satiating macronutrient — reduces hunger
- High-protein diets reduce muscle loss during calorie restriction by up to 50%
Protein target during fat loss: 1.6–2.2g per kg of body weight
For an 80kg person: 128–176g of protein per day
Good protein sources:
- Chicken breast (100g): 31g protein, 165 cal
- Eggs (1 whole): 6g protein, 70 cal
- Paneer (100g): 18g protein, 265 cal
- Dal / Lentils (100g cooked): 9g protein, 116 cal
- Greek yogurt (100g): 10g protein, 59 cal
- Tofu (100g): 8g protein, 76 cal
- Whey protein (30g scoop): 24g protein, 120 cal
How Fast Will I Lose Weight? A Realistic Timeline
| Current Weight | Weekly Loss (500 cal deficit) | Weeks to Lose 10 kg |
|---|---|---|
| 100 kg | ~0.5 kg/week | ~20 weeks |
| 80 kg | ~0.4–0.5 kg/week | ~20–25 weeks |
| 70 kg | ~0.35–0.45 kg/week | ~22–28 weeks |
Note: The first 1–2 weeks often show faster apparent weight loss (2–4 kg) due to water weight and glycogen depletion. This is normal and not all fat loss.
Use the Weight Loss Calculator to get your personalised timeline →
Why the Scale Isn't Always Accurate
Weight on the scale fluctuates by 1–3 kg daily based on:
- Water retention from sodium, carbs, stress, or hormones
- Meal timing — weighing after a large meal will show more
- Menstrual cycle — women retain water in the days before their period
- Bowel movement — your gut can hold 0.5–1.5 kg of material
Track weekly trends, not daily numbers. Weigh yourself at the same time (ideally morning, after using the bathroom), and look at the 2-week trend.
Common Mistakes That Stall Weight Loss
1. Underestimating Calorie Intake
Studies consistently show people underestimate their food intake by 20–40%. A "small snack" that seems like 150 calories often contains 400.
Fix: Track your food precisely for 2–4 weeks using an app. Even experienced dieters are often shocked.
2. Overestimating Exercise Calories
Fitness trackers and gym machines over-estimate calorie burn by 20–90%. A 30-minute treadmill run burns ~250–350 calories for most people, not 600.
Fix: Don't eat back exercise calories unless you're genuinely very active (6+ days/week).
3. Not Eating Enough Protein
Low protein during a deficit leads to muscle loss — which slows your metabolism, makes you look "skinny fat," and makes it harder to maintain weight loss.
Fix: Hit your protein target (1.6–2.2g/kg) every day.
4. Too Large a Deficit
Eating 1,000+ calories below TDEE may cause faster weight loss initially, but leads to muscle loss, extreme hunger, hormonal disruption, and metabolic adaptation — all of which make the deficit harder to sustain.
Fix: Start with 500 cal/day deficit. Add exercise for extra deficit rather than slashing food further.
5. Weekend Overeating
Being in a 500-cal deficit Monday–Friday, then overeating by 1,000 cal on Saturday and Sunday creates a weekly average deficit of only ~100 calories — almost no progress.
Fix: Treat the week as one unit. Track daily or at minimum weekly.
6. Ignoring Liquid Calories
Juices, soft drinks, chai with sugar, lassi, alcohol — liquids can add 300–800 "invisible" calories per day.
Fix: Drink water, black coffee, or unsweetened tea. Be aware of what's in drinks.
Does Exercise Help Weight Loss?
Exercise is helpful but not essential for a calorie deficit. You can lose weight through diet alone.
However, exercise — especially resistance training (weightlifting) — is critical for:
- Preserving muscle while losing fat
- Improving body composition (looking fit, not just thin)
- Increasing TDEE so you can eat more
- Long-term weight maintenance
Best combination for fat loss:
- 3–4 days/week resistance training
- 2–3 days of cardio (walking, cycling, swimming)
- A 500 calorie/day dietary deficit
How to Maintain Weight Loss After Reaching Your Goal
Studies show most people regain weight after dieting. The reasons are:
- Metabolic adaptation: your TDEE drops during a deficit and doesn't fully recover immediately
- Increased hunger hormones: ghrelin stays elevated for months after weight loss
- Return to old habits: without new habits in place, old patterns resume
To maintain successfully:
- Reverse diet — slowly increase calories by 50–100/week until you reach your new maintenance level
- Keep protein high (prevents regain of lost muscle)
- Continue training
- Weigh yourself weekly to catch small regains early
Frequently Asked Questions
How many calories should I eat to lose 1 kg per week?
A deficit of ~7,700 calories per week (1,100 cal/day) would theoretically lose 1 kg/week. However, this is quite aggressive. Most people do better aiming for 0.5 kg/week (500 cal/day deficit).
Will eating less slow down my metabolism?
Yes, to some degree. This is called "metabolic adaptation." Your TDEE drops as you lose weight (lighter body burns fewer calories) and your body becomes slightly more efficient. This is why calorie targets should be recalculated every 4–6 weeks of dieting.
Is fasting better than calorie counting?
Intermittent fasting works because it reduces calorie intake — not because of any metabolic magic. If you eat the same total calories in a smaller window, you won't lose weight.
How do I deal with hunger during a calorie deficit?
Eat high-volume, low-calorie foods (vegetables, salads, soups). Increase protein. Don't restrict carbs to zero — a balanced deficit is more sustainable. Use black coffee/tea to reduce appetite if needed.
Do I need to count macros or just calories?
For basic weight loss, just hitting a calorie target works. For body composition (keeping muscle while losing fat), tracking protein is essential. Full macro tracking (protein + carbs + fat) is optional for most.
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