NUTRITION · DEFICIT PLANNING
Calorie Deficit Calculator
Estimate the daily calorie deficit you need to reach a target bodyweight in a given number of weeks.
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Result
Projected Weight Path
Linear projection at the computed weekly rate.
How to use it
- Run the TDEE Calculator first to establish your maintenance calories, then enter that number here along with your weight-loss goal and timeline.
- A 500-calorie daily deficit theoretically produces 1 lb/week loss (3,500 cal = 1 lb fat). In practice expect 0.6–0.8 lb/week average due to water fluctuation and metabolic adaptation.
- Cap your deficit at 25% of TDEE to preserve lean mass. For a 2,200 TDEE, max sustainable deficit is 550 calories/day. Exceeding this accelerates muscle protein breakdown.
- If the scale stalls for 3+ weeks, do NOT simply cut more calories — first recalculate TDEE at your current (lower) body weight. A 10 lb loss typically lowers TDEE by 50–100 calories.
- Plan diet breaks: 1–2 weeks at maintenance calories every 6–8 weeks during a sustained cut partially reverses metabolic adaptation and significantly improves long-term adherence.
Questions people usually ask
How large a deficit should I use to lose fat without losing muscle?
Research supports 300-500 calories below TDEE for most people. This yields 0.5-1 lb weekly loss. Deficits exceeding 25% of TDEE accelerate muscle protein breakdown — a 150 lb person should not exceed ~500-600 calorie daily deficit. Protein intake of 0.8-1g per lb of body weight is the most important muscle-preservation factor.
Why did I stop losing weight on the same deficit?
Three reasons: (1) Adaptive thermogenesis — metabolism slows by 5-15% during sustained restriction. (2) Weight loss itself reduces TDEE — lighter bodies burn fewer calories. (3) Food tracking drift — portion accuracy decreases over time. Recalculate your deficit based on current weight and consider a 1-2 week diet break at maintenance.
Is it safe to eat 1200 calories a day?
1200 calories is a minimum threshold commonly cited, but adequacy depends on body size. A 130 lb, 5 foot 4 inch lightly active woman might have a TDEE around 1700 calories — a 500 calorie deficit brings her to 1200, which is adequate. A larger person eating 1200 calories would be in an extreme deficit (40%+) risking muscle loss, fatigue, and nutrient deficiencies.
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