Calorie Deficit: How Much to Lose Weight

Creating a calorie deficit is the foundation of fat loss. When you consume fewer calories than your body burns, it draws on stored energy — primarily body fat — to make up the difference. Understanding how large that deficit should be separates sustainable progress from counterproductive crash dieting.

What Is a Calorie Deficit?

A calorie deficit exists whenever your total daily energy expenditure (TDEE) exceeds your caloric intake. Your TDEE is the sum of your basal metabolic rate (BMR), the thermic effect of food (roughly 10% of calories consumed), non-exercise activity thermogenesis (NEAT), and deliberate exercise. For most adults, TDEE ranges from 1,600 to 3,000 kcal per day depending on body size and activity level.

One pound of body fat stores approximately 3,500 kilocalories of energy. A deficit of 500 kcal per day therefore produces roughly 1 lb of fat loss per week in theory, though the real-world relationship is less linear due to metabolic adaptation and changes in water retention.

How Large Should Your Deficit Be?

Research and clinical experience point to three practical deficit tiers:

• Mild deficit (250–300 kcal/day): Projected loss of 0.25–0.5 lb per week. Ideal for athletes, people close to goal weight, or anyone prioritizing muscle preservation. Metabolic adaptation is minimal.
• Moderate deficit (500 kcal/day): The most widely recommended starting point. Yields roughly 0.5–1 lb per week and is sustainable for most people without significant hunger or muscle loss when protein intake is adequate.
• Aggressive deficit (750–1,000 kcal/day): Targets 1–2 lbs per week. Appropriate for individuals with a BMI above 30 under medical supervision, but increases risk of lean mass loss, micronutrient deficiency, and fatigue.

Most guidelines recommend a maximum deficit of 1,000 kcal per day, and most practitioners cap free-living fat loss goals at 1 lb per week for people under 200 lbs, or 1% of body weight per week for heavier individuals.

Calculating Your Personal Deficit

The process has two steps: estimate TDEE, then subtract your target deficit.

1. Estimate BMR using the Mifflin-St Jeor equation (considered more accurate than Harris-Benedict for modern populations):
   Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
   Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
2. Multiply by an activity factor: Sedentary (×1.2), lightly active (×1.375), moderately active (×1.55), very active (×1.725), extremely active (×1.9).
3. Subtract your chosen deficit (typically 500 kcal) to get your daily calorie target.

Example: a 35-year-old woman, 70 kg, 165 cm, lightly active. BMR ≈ 1,470 kcal. TDEE ≈ 2,021 kcal. Target with 500-kcal deficit ≈ 1,521 kcal.

Minimum Calorie Floors

Regardless of deficit math, intake should rarely drop below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Below these thresholds, meeting protein, vitamin, and mineral requirements becomes extremely difficult, and metabolic rate suppression accelerates. Very low calorie diets (800 kcal/day or less) are a medical intervention, not a self-directed approach.

Adjusting Over Time

Metabolic adaptation — a reduction in TDEE beyond what body weight loss alone predicts — is a real phenomenon documented in studies including the famous Minnesota Starvation Experiment and subsequent research on The Biggest Loser participants. After 4–8 weeks at a consistent deficit, reassess by tracking weight trends. If loss stalls, consider a 1–2 week maintenance break (a "diet break") to partially restore leptin and thyroid hormone levels before resuming the deficit.

Protein intake of at least 1.6–2.2 g per kg of body weight is the strongest lever for preserving muscle during a calorie deficit, making protein the nutrient to prioritize when cutting calories.