Weight Change Calculator
Calculate weight loss or gain timeline using the 3500-calorie-per-pound rule and caloric deficit/surplus
Your Information
Positive = deficit (weight loss), Negative = surplus (weight gain). Calculate your TDEE first.
Quick Deficit Presets (Weight Loss)
How It Works
The 3500-Calorie Rule
Time to Goal (weeks) = Total Weight Change / Weekly Rate
This is a simplified model. Actual weight loss varies based on metabolism, water retention, muscle loss/gain, and adaptive thermogenesis.
Example Calculation
Goal: Lose 5 kg
Daily Deficit: 500 calories
Step 1: Weekly deficit = 500 × 7 = 3500 calories
Step 2: Weekly weight loss = 3500 / 7700 = 0.45 kg
Step 3: Time to goal = 5 / 0.45 = 11 weeks
Result: ~11 weeks to lose 5 kg at 500 cal/day deficit
Limitations of the 3500-Calorie Rule
- Doesn't account for metabolic adaptation (body adapts to lower calories)
- Ignores changes in water retention and glycogen stores
- Assumes all weight lost is fat (some is muscle, especially in large deficits)
- Individual variation in metabolism, hormones, and genetics
- More accurate for short-term predictions (<12 weeks)
Frequently Asked Questions
Is the 3500-calorie rule accurate? ▼
It's a useful approximation but not exact. Research shows it overestimates weight loss, especially long-term, due to metabolic adaptation and changes in energy expenditure. It's more accurate for initial weeks and serves as a starting point for planning.
What's a safe rate of weight loss? ▼
0.5-1 kg (1-2 lbs) per week is sustainable for most people. Faster loss (500-1000 cal deficit) risks muscle loss and metabolic slowdown. Slower loss (250-500 cal deficit) is easier to maintain and preserves muscle better.
Why did my weight loss stall? ▼
Metabolic adaptation: your body reduces energy expenditure in response to caloric deficit. NEAT (non-exercise activity) decreases, and BMR may drop 5-15%. Water retention from cortisol can mask fat loss on the scale. Take diet breaks every 8-12 weeks.
How do I preserve muscle during weight loss? ▼
1) Keep deficit moderate (500-750 cal/day), 2) Eat 1.6-2.2g protein per kg bodyweight, 3) Maintain strength training 3-4×/week, 4) Don't lose more than 1% bodyweight per week. Aggressive deficits sacrifice muscle.
References & Sources
More accurate model accounting for metabolic adaptation
Comprehensive weight loss timeline calculator