Calorie Deficit Calculator
A calorie deficit occurs when you consume fewer calories than your body burns each day. Over time, the accumulated deficit causes your body to draw on stored fat for energy, resulting in weight loss. The fundamental energy balance principle underpinning this calculator is that one kilogram of body fat stores approximately 7,700 kilocalories. To lose that kilogram, you need to create a total deficit of 7,700 kcal across several days or weeks. Enter your current weight, your goal weight, and the number of weeks you want to allow. The calculator divides the total energy deficit needed by the number of days and tells you exactly how many calories below your maintenance level you need to eat each day. It also shows your recommended daily calorie target so you can set your food intake accordingly. This is a planning tool: it assumes consistent adherence and a stable metabolism. Real weight loss is rarely perfectly linear, so treat the output as a starting target and adjust based on results every two to four weeks.
Formula
Fat to lose (kg) = Current weight - Goal weight
Total deficit (kcal) = Fat to lose * 7,700
Daily deficit (kcal) = Total deficit / (Weeks * 7)
Daily calorie target = Maintenance calories - Daily deficit
Weekly loss rate = Fat to lose / Weeks
Calorie Deficit Calculator: frequently asked questions
How many calories equal 1 kg of fat?
One kilogram of body fat contains approximately 7,700 kilocalories of stored energy. This is the figure used to translate a calorie deficit into projected weight loss. In practice, water retention, metabolic adaptation, and lean mass changes mean actual results vary.
Is a 500 calorie per day deficit safe?
For most healthy adults, a deficit of 500 to 1,000 calories per day is considered safe and produces 0.45 to 0.9 kg (1 to 2 lb) of weight loss per week. Larger deficits may cause muscle loss, fatigue, and nutrient deficiencies. Always consult a doctor before making significant dietary changes.
What is the minimum number of calories I should eat?
Most dietitians recommend men eat no fewer than 1,500 calories per day and women no fewer than 1,200 calories per day without medical supervision. Eating below your BMR consistently can slow your metabolism and deprive your organs of essential energy.
Why do I stop losing weight even in a deficit?
Your body adapts to a reduced calorie intake by lowering its metabolic rate, a process called metabolic adaptation. As you lose weight, your BMR also falls because there is less mass to maintain. This means the same deficit produces less weight loss over time. Recalculate your targets as your weight changes.
Should I eat back calories burned through exercise?
It depends on your goal. If your daily calorie target was set from your TDEE (which already includes activity), you should not eat back exercise calories. If your target was set from your BMR only, eating back a portion of exercise calories avoids too large a deficit on active days.
Official sources
- CDC: Losing Weight
- Hall KD, et al. (2011). "Quantification of the effect of energy imbalance on bodyweight." The Lancet, 378(9793):826-837.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.