Calorie Deficit Calculator

Tell the calculator your maintenance calories and how much weight you want to lose by when, and it works out the daily calorie target and the size of the deficit — flagging anything faster than a safe rate.

Fill in the fields, then press Calculate deficit.

How a calorie deficit works

You lose weight when you eat fewer calories than you burn — a calorie deficit. A long-standing rule of thumb is that about 3,500 calories equals roughly one pound of body fat (about 7,700 calories per kilogram). Spread the total deficit across your timeframe to get a daily number.

daily deficit = (pounds × 3,500) ÷ (weeks × 7)

Subtract that daily deficit from your maintenance calories — the amount that keeps your weight steady — to get your daily intake target. If you don't know your maintenance figure, estimate it first with a TDEE calculator.

Worked example

Lose 15 lb in 12 weeks at 2,400 maintenance calories:

Total deficit: 15 × 3,500 = 52,500 calories.
Daily deficit: 52,500 ÷ (12 × 7) = 52,500 ÷ 84 ≈ 625 cal/day.
Daily target: 2,400 − 625 ≈ 1,775 calories per day.

Safe rates of loss

Most health authorities suggest losing about 0.5–2 lb (0.25–1 kg) per week. Faster loss usually means giving up muscle and is hard to sustain. This calculator warns you if your plan needs a daily deficit that drops intake below roughly 1,200 calories (women) or 1,500 (men), or if the weekly rate exceeds 1% of body weight — either is a sign to extend your timeline. The 3,500-calorie rule is a useful approximation; real-world loss varies with water, metabolism and adherence.

Tip: find your maintenance calories with the TDEE calculator or the calorie calculator, then set protein with the macro calculator.

Frequently asked questions

How big a deficit is safe?

A deficit of about 500–750 calories a day produces a sustainable loss of roughly 1–1.5 lb per week for most people. Larger deficits risk muscle loss, fatigue and rebound, and shouldn't push intake below about 1,200 (women) or 1,500 (men) calories.

Is the 3,500-calorie rule exact?

No — it's a useful approximation. Real fat loss varies with water weight, metabolic adaptation and how accurately you track food, so treat the number as a starting plan and adjust based on real-world results over a few weeks.

What if I don't know my maintenance calories?

Estimate them first with a TDEE calculator, which combines your resting metabolism with an activity factor. Then subtract the daily deficit this tool gives you to find your intake target.

Why does the calculator warn me?

It flags plans that drop your daily intake too low or demand a weekly loss faster than about 1% of body weight. Both make the diet hard to sustain and more likely to cost muscle, so it suggests extending the timeline.

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Mustafa Bilgic · Editor, Calcool
Uses the ~3,500-kcal-per-pound approximation and standard 0.5–2 lb/week safe-loss guidance. Educational, not medical advice. Everything runs in your browser — nothing you enter is uploaded, logged or stored.

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