Free Calorie Deficit Calculator

Enter your stats and goal weight to find your daily calorie target, weekly deficit, and estimated goal date you'll reach your goal.

Calculator What is a deficit? Safe deficit size FAQ

Your stats

Biological sex

Age

Current weight (lbs)

Goal weight (lbs)

Height

Activity level

Weight loss pace

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kcal/day — your calorie target

What is a calorie deficit and how does it cause fat loss?

A calorie deficit means consuming fewer calories than your body burns in a day (your TDEE). When your body doesn't get enough energy from food, it taps into stored fat to make up the difference — this is how fat loss happens.

The relationship is straightforward: 1 lb of fat stores approximately 3,500 kcal of energy. A consistent 500 kcal/day deficit therefore produces approximately 1 lb of fat loss per week. This is the most widely cited guideline in nutrition science, derived from early research by Max Wishnofsky (1958) and still broadly supported by modern data.

Example: Male, 30y, 85 kg, 178 cm, moderately active — goal weight 75 kg

TDEE (maintenance)2,757 kcal/day

Calorie target at −500/day2,257 kcal/day

Weekly deficit3,500 kcal = ~1 lb fat

Total to lose10 kg = 22 lbs

Estimated weeks~22 weeks (5.5 months)

Important: The 3,500 kcal/lb rule is a starting estimate, not a precise prediction. Real fat loss varies based on water retention, muscle loss, metabolic adaptation, and dietary composition. Track your weight weekly (averaged over 4 weeks) and adjust calories by ±100–150 kcal if results don't match expectations after 3–4 weeks.

How big should your calorie deficit be?

The optimal deficit balances fat loss speed against muscle preservation, hormonal health, energy levels, and diet sustainability. Research and practical experience converge on these guidelines:

Moderate deficit — 500 kcal/day (~1 lb/week) — recommended for most people

The standard starting point. Large enough to produce visible results, small enough to preserve most muscle mass when protein is adequate. Suits anyone with 10–50+ lbs to lose who is not in a rush.

Slow deficit — 250 kcal/day (~0.5 lb/week)

Best for people close to their goal weight, athletes who need to maintain performance, or anyone with a history of disordered eating. Lower deficit means higher training quality and better muscle retention in the final stretch.

Aggressive deficit — 750–1000 kcal/day (~1.5–2 lbs/week)

Appropriate only for people with significant excess body fat (BMI 30+) or specific medical reasons. At this deficit, muscle loss becomes a real risk unless protein intake is very high (2.4+ g/kg) and resistance training is maintained. Very low calorie intake may be inappropriate for many people — consult a healthcare professional — this may be associated with metabolic adaptation.

The deficit you can sustain is always better than the one you can't

A 300 kcal/day deficit maintained for 6 months produces more fat loss than a 1,000 kcal/day deficit abandoned after 6 weeks. Hunger, mood, and energy levels are your body's signals — if you're constantly miserable, reduce the deficit and extend the timeline.

Frequently asked questions

How do I calculate my calorie deficit?

Calculate your TDEE first (how many calories you burn per day), then subtract your chosen deficit. Example: TDEE of 2,500 kcal minus a 500 kcal deficit = eat 2,000 kcal/day. This calculator does both steps automatically using the Mifflin–St Jeor equation.

How many calories should I eat to lose 1 pound per week?

Eat 500 kcal/day below your TDEE. Since 1 lb of fat contains approximately 3,500 kcal, a 500 kcal daily deficit creates a weekly deficit of 3,500 kcal — translating to roughly 1 lb of fat loss per week under stable conditions.

Is a 1,000 calorie deficit safe?

For most people, a 1,000 kcal/day deficit is aggressive and risks muscle loss, fatigue, hormonal disruption, and diet failure. It's generally only appropriate for people with BMI above 30 under medical supervision, and only when protein intake is very high (2.4 g/kg+). Most people achieve better long-term results with a 500 kcal deficit they can maintain consistently.

Why is my weight loss slower than the calculator predicts?

Several factors slow apparent progress: water retention (especially if increasing carbs or starting exercise), muscle gain offsetting fat loss, measurement errors in calorie tracking (studies show people underestimate intake by 20–40%), and metabolic adaptation. Measure your 4-week weight trend rather than daily fluctuations, and adjust calories if the trend doesn't match your deficit after 3–4 weeks.

Do I need to recalculate as I lose weight?

Yes — every 10 lbs (4.5 kg) lost reduces your BMR by approximately 50–80 kcal/day. If you don't recalculate, what started as a 500 kcal deficit gradually becomes smaller and weight loss stalls. Recalculate every 4–8 weeks or whenever you notice your progress has plateaued for 2+ weeks.

What should I eat at my calorie deficit?

Prioritise protein (1.6–2.2 g/kg bodyweight) to preserve muscle mass — this is the single most important dietary factor during a cut. Fill remaining calories with whole foods: vegetables, fruits, whole grains, legumes, and healthy fats. Minimise ultra-processed foods which are calorie-dense but low in satiety. Use the macro calculator for exact protein, carb and fat targets.

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Results are estimates based on validated formulas. Not medical advice.