Calorie Deficit Calculator
A calorie deficit occurs when you consume fewer calories than your body uses. The widely cited estimate is that one pound of body fat stores approximately 3,500 kilocalories, so a cumulative deficit of 3,500 kcal corresponds to roughly one pound of fat loss. This calculator uses that benchmark: enter your planned daily calorie deficit and the number of days you plan to maintain it, and it estimates your total calorie deficit plus projected weight loss in both pounds and kilograms. The model is a linear approximation; actual weight loss slows over time as the body adapts, so use these figures as a planning guide rather than a precise prediction.
Calorie deficit formula
Total deficit (kcal) = Daily deficit * Days
Loss (lb) = Total deficit / 3,500
Loss (kg) = Loss (lb) * 0.453592
One pound of fat equals approximately 3,500 kcal. Dividing the total deficit by 3,500 gives the estimated fat loss in pounds. Multiplying by 0.453592 converts to kilograms.
Using the calorie deficit calculator
- A 500 kcal/day deficit over 7 days equals a 3,500 kcal deficit, targeting 1 lb of fat loss per week.
- A 250 kcal/day deficit over 30 days produces a 7,500 kcal deficit, roughly 2.14 lb loss.
- Deficits larger than 1,000 kcal/day increase risk of muscle loss and nutrient deficiencies.
- Actual results depend on adherence, metabolic adaptation, water retention, and starting body composition.
- Combine the deficit with adequate protein intake to maximise fat loss while preserving muscle.
Calorie deficit calculator: frequently asked questions
What is the 3,500 calorie per pound rule?
One pound of body fat contains approximately 3,500 kilocalories of stored energy. Creating a cumulative deficit of 3,500 kcal is therefore estimated to result in approximately one pound of fat loss. This figure has been used in dietary guidance for decades and is referenced by the USDA.
How many calories should I cut per day to lose 1 pound per week?
A deficit of 500 kcal per day produces a weekly deficit of 3,500 kcal, which corresponds to approximately 1 pound of fat loss per week. A deficit of 1,000 kcal per day corresponds to about 2 pounds per week.
Is the 3,500 calorie rule accurate?
The 3,500 kcal rule is a useful approximation for short-term planning, but actual weight loss is non-linear because metabolism adapts over time. Longer-term predictions should account for metabolic adaptation. The rule is still widely used by the USDA and NIH as a planning benchmark.
What is a safe daily calorie deficit?
Dietary guidelines generally consider deficits of 500-1,000 kcal per day to be appropriate for most healthy adults, targeting 0.5-1 kg (1-2 lb) per week. Very low calorie diets (below 800 kcal/day) should only be used under medical supervision.
Does the 3,500 rule apply to kilograms too?
One kilogram of fat stores approximately 7,700 kcal. To lose one kilogram per week you would need a deficit of about 1,100 kcal per day, which is aggressive for most people. A more sustainable 500 kcal/day deficit removes about 0.45 kg per week.
Official sources
- USDA Dietary Guidelines 2020-2025: DietaryGuidelines.gov.
- NIH Weight Management: NHLBI Healthy Weight Resources.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.