Calorie Deficit Calculator

A calorie deficit occurs when you consume fewer calories than your body burns (TDEE). Since your body needs energy, it taps into fat stores to make up the difference. A deficit of 500 calories/day theoretically produces about 1 pound of fat loss per week (3,500 calories = approximately 1 lb of fat). The calculator determines your ideal deficit based on your goals.

A moderate deficit of 300-500 calories/day (1-2 lb/week loss) is considered safe and sustainable. Deficits over 1000 calories/day risk muscle loss, nutrient deficiencies, metabolic slowdown, and are difficult to maintain. The calculator warns if your target requires an excessively aggressive deficit.

TDEE is estimated using the Mifflin-St Jeor equation for BMR multiplied by an activity factor. The calculator uses your age, weight, height, gender, and activity level. Your daily calorie target is TDEE minus your chosen deficit. Track your actual weight loss for 2-3 weeks and adjust if results differ from projections.

Some muscle loss occurs during any deficit, but you can minimize it by eating adequate protein (1.6-2.4g/kg), performing resistance training 2-4 times per week, keeping the deficit moderate (not extreme), and getting sufficient sleep. The calculator recommends a protein target alongside your calorie goal for this reason.

As you lose weight, your TDEE decreases because your body is smaller and requires less energy. A 500-calorie deficit that produced 1 lb/week loss initially may only produce 0.5 lb/week later. The calculator accounts for this adaptive thermogenesis and shows revised calorie targets as your weight decreases.