The Short Answer
To lose weight, eat fewer calories than you burn. The size of the gap determines how fast you lose:
| Daily Deficit | Weekly Loss | Monthly Loss |
|---|---|---|
| 250 calories | 0.5 lb (0.23 kg) | 2 lb (0.9 kg) |
| 500 calories | 1 lb (0.45 kg) | 4 lb (1.8 kg) |
| 750 calories | 1.5 lb (0.68 kg) | 6 lb (2.7 kg) |
| 1,000 calories | 2 lb (0.9 kg) | 8 lb (3.6 kg) |
The sweet spot for most people: 500 calories/day (1 lb/week).
Calculate Your Deficit
Enter your stats to get a personalized calorie target and timeline:
How Calorie Deficits Work
The 3,500 Calorie Rule
One pound of body fat stores approximately 3,500 calories of energy. To lose one pound, you need a total deficit of 3,500 calories — or 500 calories per day over a week.
500 cal/day × 7 days = 3,500 cal = ~1 lb lost
This is a simplification (metabolism adapts over time), but it's a reliable starting point.
Step 1: Find Your TDEE
Your Total Daily Energy Expenditure (TDEE) is how many calories you burn per day:
TDEE = BMR × Activity Factor
The Mifflin-St Jeor equation for BMR:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
| Activity Level | Factor | Example |
|---|---|---|
| Sedentary (desk job, no exercise) | 1.2 | Office worker |
| Lightly active (1-3 days/week) | 1.375 | Casual gym-goer |
| Moderately active (3-5 days/week) | 1.55 | Regular exerciser |
| Very active (6-7 days/week) | 1.725 | Athlete |
| Extra active (physical job + exercise) | 1.9 | Construction worker who exercises |
Step 2: Subtract Your Deficit
Daily calorie target = TDEE − deficit
Example: TDEE of 2,500 with a 500-calorie deficit = eat 2,000 calories/day.
Choosing Your Deficit Level
Mild: 250 cal/day (0.5 lb/week)
- Easiest to sustain
- Minimal muscle loss
- Best for people close to goal weight
- Barely noticeable dietary change
Moderate: 500 cal/day (1 lb/week) ✓ Recommended
- Sustainable for most people
- Good balance of speed and adherence
- Noticeable results within a month
- Standard recommendation from dietitians
Aggressive: 1,000 cal/day (2 lb/week)
- Faster results but harder to maintain
- Higher risk of muscle loss
- May impact energy and mood
- Should not go below 1,200 cal/day (women) or 1,500 cal/day (men)
How Long Will It Take?
| Weight to Lose | 250 cal/day | 500 cal/day | 1,000 cal/day |
|---|---|---|---|
| 10 lb (4.5 kg) | 20 weeks | 10 weeks | 5 weeks |
| 20 lb (9 kg) | 40 weeks | 20 weeks | 10 weeks |
| 30 lb (14 kg) | 60 weeks | 30 weeks | 15 weeks |
| 50 lb (23 kg) | 100 weeks | 50 weeks | 25 weeks |
Reality check: Weight loss isn't perfectly linear. You'll see faster loss in the first few weeks (water weight), then it slows down. Plateaus are normal — your metabolism adapts.
Protein: The Most Important Macro During a Deficit
When cutting calories, protein becomes critical:
| Why | How Much |
|---|---|
| Preserves muscle mass | 0.7-1g per lb of body weight |
| Increases satiety (you feel fuller) | ~30-40% of total calories |
| Higher thermic effect (burns more to digest) | 20-30% of protein calories burned in digestion |
Example: At 2,000 cal/day with 40% protein = 800 cal from protein = 200g protein.
A recommended macro split during a deficit:
| Macro | Percentage | At 2,000 cal | Grams |
|---|---|---|---|
| Protein | 40% | 800 cal | 200g |
| Carbs | 35% | 700 cal | 175g |
| Fat | 25% | 500 cal | 56g |
Common Mistakes
1. Cutting Too Aggressively
Going below 1,200 calories triggers survival mechanisms: your metabolism slows, you lose muscle, and you're more likely to binge. Slow and steady wins.
2. Not Counting Liquid Calories
A daily latte (250 cal), juice (150 cal), and evening beer (150 cal) = 550 calories you might not be tracking. That's your entire deficit gone.
3. Overestimating Exercise Calories
The treadmill says you burned 500 calories? It's probably 300. Exercise machines overestimate by 15-30%. Don't "eat back" all your exercise calories.
4. Weekend Overeating
A 500 cal/day deficit Monday-Friday = 2,500 total. Two weekend days at maintenance = net deficit of only 2,500 instead of 3,500. Results: 0.7 lb/week instead of 1 lb/week.
5. Ignoring Sleep
Poor sleep increases ghrelin (hunger hormone) by up to 28% and decreases leptin (fullness hormone). Aim for 7-9 hours.
When to Adjust
If you've been consistent for 2-3 weeks with no change:
- Recalculate your TDEE — it decreases as you lose weight
- Track more carefully — food scales are more accurate than measuring cups
- Add movement — even 30 min of walking adds 100-200 cal to your daily burn
- Check non-scale wins — measurements, how clothes fit, progress photos
Key Takeaways
- A 500 cal/day deficit (1 lb/week) is the most sustainable approach for most people
- Never go below 1,200 cal/day without medical supervision
- Prioritize protein (40% of calories) to preserve muscle
- Weight loss isn't linear — plateaus are normal
- Recalculate your TDEE as you lose weight (your needs decrease)
- Sleep, stress, and hydration all affect results