Calorie Deficit Calculator
Enter your TDEE (from the Calorie Calculator), your goal weight, and preferred rate of loss to see your daily calorie target and estimated time to reach your goal.
How Calorie Deficit Calculator works
Calorie deficit and fat loss
Body fat contains approximately 7,700 kilocalories per kilogram. To lose 0.5 kg of fat per week requires a daily deficit of 7,700 × 0.5 ÷ 7 ≈ 550 kcal. This is the theoretical value; actual fat loss also involves changes in water retention, glycogen stores, and metabolic adaptation, so real-world results vary. The direction of the relationship is reliable — sustained deficit leads to weight loss.
TDEE and where to find it
Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a day, including activity. Use the Calorie Calculator on this site to estimate your TDEE from your age, sex, height, weight, and activity level. Note that TDEE is an estimate — if your actual weight does not change on a given calorie intake, that intake is your maintenance level.
Rate of loss and muscle preservation
Faster rates of loss (above 1 kg/week) increase the proportion of weight lost from muscle rather than fat, particularly without adequate protein and resistance training. A rate of 0.5–0.75 kg/week is generally considered the optimal range for fat loss while preserving muscle mass. Slower rates (0.25–0.5 kg/week) are more sustainable for most people and cause less metabolic adaptation.
Metabolic adaptation
The body adapts to sustained calorie deficits by reducing energy expenditure — a process sometimes called metabolic adaptation or "starvation mode." This is why the theoretical timeline based on a fixed deficit tends to underestimate actual time to goal in practice. Periodic diet breaks (returning to maintenance for 1–2 weeks) can help manage adaptation and improve long-term adherence.
Frequently asked questions
How many calories should I eat to lose 1 kg per week?
Losing 1 kg of fat per week requires a daily deficit of approximately 1,100 kcal (7,700 kcal/kg ÷ 7 days). For most people, this is a very aggressive target — eating only 1,000–1,200 kcal/day — which is hard to sustain and may lead to muscle loss and nutritional deficiencies. A target of 0.5 kg/week (550 kcal/day deficit) is more practical and sustainable.
What is the minimum number of calories I should eat?
The NHS and British Dietetic Association recommend not going below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Very low calorie diets (VLCDs) below 800 kcal/day carry health risks and should only be undertaken under medical supervision.
Why is my weight loss slower than the calculation predicts?
Several factors slow actual weight loss: metabolic adaptation (the body reduces energy expenditure in response to deficit), water retention fluctuations, digestive system contents varying day to day, and individual variation in calorie absorption. Over weeks and months, the trend should follow the prediction, but daily and weekly fluctuations of 1–2 kg from water alone are normal.
Should I eat back exercise calories?
If your TDEE was calculated using an activity factor that accounts for your exercise, no. If your TDEE is sedentary baseline (and exercise is additional), then partially eating back exercise calories helps prevent an excessive deficit. Many people who "eat back" all exercise calories find it harder to lose weight because calorie burn estimates (from fitness trackers) tend to be overestimated.
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This calculator provides estimates for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.