Calorie Deficit Calculator: How Many Calories to Lose Weight
Tell the calculator your current weight, goal and activity. It returns a daily calorie target, the size of your deficit and a realistic timeline.
How to calculate a calorie deficit
Deficit = maintenance calories (TDEE) − what you eat. One kilogram of body fat stores roughly 7,700 calories (about 3,500 per pound), so a 500-calorie daily deficit adds up to about 0.5 kg (1 lb) a week. The calculator estimates your TDEE, subtracts the deficit you choose and shows the resulting target.
How big a deficit is safe?
The CDC links gradual loss of 1–2 lb (0.5–1 kg) a week with keeping the weight off. That usually means a 500–1,000-calorie daily deficit — but never below about 1,200 calories for women or 1,500 for men without medical supervision, and never below your BMR for long. Smaller, steadier deficits preserve muscle and are easier to keep.
When will I reach my goal weight?
Divide the total you want to lose by your weekly rate. Losing 10 kg at 0.5 kg/week takes about 20 weeks. Expect the real timeline to be 10–20% longer: metabolism adapts and adherence is never perfect. Re-run the calculator every 5 kg (10 lb) so the deficit stays accurate.
Calorie deficit vs TDEE
TDEE is the baseline; the deficit is what you take off it. If you already eat close to your TDEE, weight is stable by definition — the deficit is created either by eating less, moving more, or both. Adding 30 minutes of brisk walking most days is worth roughly 100–150 calories for an average adult.
Sources
- CDC, Losing weight — https://www.cdc.gov/healthy-weight-growth/losing-weight/index.html
- Dietary Guidelines for Americans (current edition) — https://www.dietaryguidelines.gov/
- Mifflin-St Jeor equation, PubMed 2305711 — https://pubmed.ncbi.nlm.nih.gov/2305711/
This calculator is educational and not medical advice. If you have a health condition, are pregnant, or are under 18, ask a clinician before changing your diet.
What the result tells you
A daily calorie target below your maintenance, sized to your chosen pace of fat loss.
How to use it
- Pick a pace you can hold for weeks, not the fastest one.
- Judge progress from your weekly-average weight, not a single reading.
- If loss stalls for 2–3 weeks, trim another 100–150 kcal.
Recommendations
- Keep protein high to protect muscle while losing fat.
- Fill up on vegetables and fibre to manage hunger.
- A faster pace isn't better if it leaves you exhausted or bingeing.
Health & wellbeing
Constant cold, low energy, poor sleep, or preoccupation with food mean the deficit is too aggressive — ease off. Don't go below about 1,200 (women) or 1,500 (men) kcal without medical supervision.
Troubleshooting
Not losing? Recheck portions and activity honestly before cutting more. Losing too fast? Add 100–150 kcal back.
How it’s calculated
Maintenance calories come from Mifflin–St Jeor × activity, then a fixed deficit is subtracted for your chosen pace.
Target = TDEE − 275 (gentle), 550 (moderate), or 825 (faster) kcal/day, roughly 0.25–0.75 kg/week (1 kg fat ≈ 7,700 kcal).
Source: Mifflin–St Jeor (1990); energy-balance principles.
Common questions
Why am I not losing weight in a deficit?
Most often the deficit only exists on paper: untracked snacks, drinks and cooking oil, or an overestimated activity level. Water retention also hides fat loss for weeks.
Should I eat back exercise calories?
No — the activity level already includes your training.
Is a 1,000-calorie deficit too much?
It is the upper end of the CDC's steady-loss range; suitable only if it still leaves you above 1,200–1,500 calories and your BMR.