Calorie Deficit Calculator
Find the daily calories and deficit needed to reach your goal weight by a date.
Reviewed by the ToolNestr Editorial Team — July 2026
Enter your details and click Calculate.
About the calorie deficit
A calorie deficit happens when you eat fewer calories than your body burns each day (your Total Daily Energy Expenditure, or TDEE). Over time, the body makes up the shortfall by breaking down stored body fat for energy — that is how weight loss happens. This calculator estimates the daily calorie target you need to hit your goal weight in the number of weeks you choose, and checks whether the required deficit is safe and sustainable.
️️ For general information only, not medical advice.
The formulas behind the calculator
The tool uses four linked equations based on the common estimate that 1 kg of body fat stores about 7,700 calories.
Total deficit needed: (current weight − goal weight) × 7,700 cal
Daily deficit: total deficit ÷ (weeks × 7)
Daily calorie target: TDEE − daily deficit
Expected weekly loss: (daily deficit × 7) ÷ 7,700 kg
Worked example
A person with a TDEE of 2,500 cal/day wants to lose 5 kg in 10 weeks.
When to use this tool
This calculator is useful whenever you are planning a weight-loss phase (a "cut") and need a concrete daily calorie number to aim for. Instead of guessing a random amount (e.g. 1,800 cal) this tool works backwards from your goal: it tells you how much of a deficit you need, and whether that deficit is realistic given your TDEE and timeframe.
Planning a cut: If you know your TDEE from a BMR calculator and an activity multiplier, you can plug it in here to get a precise eating target for the duration of your cut.
Setting daily calories: Rather than following a one-size-fits-all meal plan, this gives you a personalised daily calorie budget based on your body and schedule.
Checking a goal date: If you have an event or deadline (e.g. a holiday in 8 weeks), the tool shows you whether reaching your goal weight by then is feasible without an unsafe deficit.
Tips for a healthy calorie deficit
Aim for 0.5–1% of body weight per week
For most people, losing about 0.5–1% of body weight per week is sustainable and preserves muscle. For an 80 kg person, that is 0.4–0.8 kg per week — which matches a deficit of roughly 440–880 cal/day.
Avoid deficits of 1,000+ calories per day
Aggressive deficits may cause rapid muscle loss, hormonal disruptions, fatigue and rebound binge-eating. The tool flags deficits over 1,000 cal/day in red as a warning.
Prioritise protein and strength training
Even in a deficit, eating enough protein (around 1.6–2.2 g per kg of body weight) and continuing resistance training helps preserve lean mass so most of the weight lost is fat.
Reassess every 4–6 weeks
As you lose weight, your TDEE drops. Recalculate every few weeks so your deficit does not shrink (or grow) unintentionally. A 5 kg lighter body needs about 100–150 fewer calories per day.
Related tools
- BMR Calculator — find your resting calorie burn
- Calorie Calculator — estimate your TDEE with activity
- Ideal Weight Calculator — healthy weight range for your height
Frequently asked questions
How big a deficit is safe?
Often 500–750 cal/day; going beyond about 1,000 risks muscle loss and is hard to sustain.
Why is the scale not moving?
Water, food timing, and muscle gain mask fat loss — judge over 2–3 weeks.
Is 7,700 calories really 1 kg?
It is the common estimate for a kg of body fat; real results vary by person.
What if my goal is unrealistic?
The tool flags deficits over 1,000/day as too aggressive. Aim for 0.5–1 kg per week.
Sources & references
This tool uses standard formulas and reference values from:
- • NIH / National Institutes of Health and CDC reference values and formulas. nih.gov
- • Peer-reviewed equations (e.g. Mifflin-St Jeor, Harris-Benedict) as originally published.
- • ACOG for pregnancy, ovulation and due-date methodology. acog.org
Not medical advice. Estimates only — consult a qualified healthcare professional for any personal health decision.