Weight loss is math: burn more calories than you consume. But the formula isn't one-size-fits-all—your unique metabolism depends on age, gender, activity level, and body composition. This calculator computes your TDEE (total daily energy expenditure) using the science-backed Mifflin-St Jeor formula, then shows how different deficit levels affect your weight loss timeline. A 500-calorie daily deficit = 1 pound lost per week; 750 calories = 1.5 pounds. Skip guessing and hit your goal date with precision.
The safe zone matters. Losing faster than 2 pounds per week triggers muscle loss, metabolic slowdown, and metabolic fatigue—unsustainable for most people. A 1-pound-per-week deficit (500 calories) is the sweet spot: sustainable, preserves muscle (especially with high protein), and feels manageable. This calculator shows your options—fast (aggressive), moderate (sustainable), or slow (flexible)—so you choose a deficit you can actually stick to for months, not weeks.
Don't just count calories; understand what you're optimizing for. In a deficit, every gram of protein matters to preserve muscle. This tool factors in nutrition reality: your deficit isn't just calorie volume but also food quality and satiety. It projects not just weight loss speed but also when metabolic adaptation kicks in (around week 4–6), requiring recalculation. Input your actual stats and get a personalized roadmap to your goal weight—realistic and backed by physiology, not fad diet nonsense.
Understanding TDEE and Calorie Deficit
TDEE (Total Daily Energy Expenditure) = calories you burn daily. Create a deficit by eating fewer calories than TDEE. Deficit of 500 cal/day = 1 lb/week weight loss (3,500 cal = 1 lb). Deficit of 1,000 cal/day = 2 lbs/week. Safe range: 500–750 cal/day (1–1.5 lbs/week). Never go below 1,200 cal/day.
The Mifflin-St Jeor Formula: Calculating BMR
BMR (Basal Metabolic Rate) = calories you burn at rest. TDEE = BMR × activity factor. Sedentary: BMR × 1.2. Lightly active: BMR × 1.375. Moderately active: BMR × 1.55. The calculator uses this science-based formula; it's more accurate than online "calculators" using random multipliers.
Safe Weight Loss Speed: 1–1.5 lbs/Week
Faster than 2 lbs/week causes muscle loss, fatigue, metabolic slowdown. 1 lb/week (500 cal deficit) is sustainable, preserves muscle. 1.5 lbs/week (750 cal deficit) is aggressive but doable. Anything below 1 lb/week is very slow (psychologically hard). Find your balance between speed and sustainability.
Macronutrients Matter: Protein Is Essential
In a calorie deficit, protein preserves muscle mass. Aim 0.8–1g protein per pound of goal body weight. On a deficit, prioritize protein, vegetables, and whole grains over refined carbs/sugar. Protein keeps you fuller longer (higher satiety). Don't just count calories; eat quality food.
Metabolic Adaptation: Why Weight Loss Slows
As you lose weight, TDEE decreases (smaller body burns fewer calories). After 10–15 lbs lost, recalculate TDEE. Some people experience "metabolic slowdown"—burning 100–200 fewer calories at the same activity level. This is normal. Solution: increase activity or slightly reduce calories again.