Calorie Deficit Calculator
Find your exact daily calorie target for fat loss and see a realistic timeline to your goal weight. Based on your TDEE and a sustainable, evidence-based deficit rate.
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Calorie Deficit and Weight Loss Guide
What do I need to know about The Energy Balance Equation?
Weight change is determined by the balance between energy consumed (calories eaten) and energy expended (TDEE). To lose weight: calories in < calories out. 1 kg of body fat contains approximately 7,700 kcal. A 500 kcal/day deficit produces approximately 0.5 kg fat loss per week. However: early weight loss also includes water and glycogen; initial losses are faster than 0.5 kg/week. Metabolic adaptation: extended calorie restriction reduces TDEE by 10-15%, which is why progress slows over time. This is normal and expected, not a sign the diet has 'stopped working' — it usually means the deficit needs adjusting as body weight and TDEE change.
What do I need to know about The Minimum Effective Deficit?
Larger deficits do not always produce faster fat loss in practice. Below approximately 1,200 kcal/day for women and 1,500 kcal/day for men: significant muscle loss, nutrient deficiencies, metabolic adaptation, fatigue, poor adherence, and rebound eating are common. Research consistently shows that a 500-750 kcal/day deficit produces the best combination of fat loss rate, muscle preservation, and long-term adherence. Very low calorie diets (under 800 kcal) should only be undertaken under medical
What's the key thing to understand about Protein and Muscle Preservation?
During a calorie deficit, eating sufficient protein is critical to preserve lean muscle mass. Without adequate protein, the body uses muscle tissue for energy — reducing metabolic rate and producing a less favourable body composition. Target: 1.6-2.2g protein per kg bodyweight during a deficit. For a 85 kg person: 136-187g protein per day. High protein also improves satiety — protein is more filling per calorie than fat or carbohydrate. Research shows that calorie-equated diets with higher protein content preserve significantly more lean muscle mass during a deficit than lower-protein diets, even when total calories and weight loss are identical.
What do I need to know about Diet Breaks and Reverse Dieting?
Metabolic adaptation: after 4-8 weeks of a calorie deficit, TDEE decreases by 10-15% due to reduced body mass (less to move), reduced thermogenesis, and hormonal changes (lower leptin, higher ghrelin). Diet breaks: periods of 1-2 weeks at maintenance calories restore hormones, improve adherence, and partly reverse metabolic adaptation — without regaining fat. Research supports alternating 2 weeks deficit with 1-2 weeks at maintenance for long-term success. Reverse dieting: very gradually increasing calories back toward maintenance after a long diet, rather than jumping straight back to normal eating, which helps limit rapid fat regain and psychological rebound overeating.