Calorie Deficit Calculator
Compare estimated daily maintenance energy with planned average intake across a chosen number of weeks.
Content updated August 7, 2026
This is arithmetic between two estimates; it does not predict body weight. Energy needs adapt over time, and logged intake and estimated expenditure can be inaccurate. The 1,000 kcal/day floor mirrors the NIH Body Weight Planner input floor, not a personalized safe minimum. Seek qualified care for an eating disorder, pregnancy, a medical condition or an individualized nutrition plan.
A calorie deficit is the arithmetic difference between estimated maintenance energy and average energy intake. Enter both estimates to see the daily, weekly and chosen-horizon gap; if intake is higher, the same tool labels the result as a surplus.
The output is intentionally an energy comparison rather than a body-weight forecast. Human energy expenditure adapts, intake logs contain error, and the familiar fixed calories-per-pound rule does not model those dynamics.
The Calorie Deficit formula
Daily balance = maintenance − intake; Weekly balance = daily balance × 7; Horizon balance = daily balance × 7 × weeksA positive balance is labeled a deficit, a negative balance a surplus, and zero a balance. All values use kilocalories.
Worked example
With estimated maintenance of 2,400 kcal/day and planned intake of 1,900 kcal/day, the arithmetic deficit is 500 kcal/day, 3,500 kcal/week and 14,000 kcal over four weeks.
Assumptions, rounding, and limitations
Assumptions
- Entered maintenance and intake are daily averages held constant across the selected whole number of weeks.
- Both inputs use dietary kilocalories and the time horizon contains exactly seven days per week.
- The calculation compares estimates and makes no assumption about a corresponding body-weight change.
Rounding: The engine retains full precision. Displayed energy and percentage values are rounded to the nearest whole unit.
Limitations
- Maintenance expenditure and logged intake are uncertain and can change over time.
- The result does not model metabolism, body composition, water, adherence or weight change.
- The 1,000 kcal/day input floor follows the NIH planner's floor but is not an individualized safety threshold or diet recommendation.
Sources
- NIH Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases
- Predicting metabolic adaptation, body weight change, and energy intake in humans — PubMed / American Journal of Physiology
Read the sign before the size
Maintenance minus intake gives the daily balance. A positive value is a deficit, a negative value is a surplus, and zero means the two entered estimates are equal. Weekly and horizon values multiply that same assumed daily difference.
The percentage divides the daily balance by entered maintenance. It describes the two inputs; it is not a recommendation for an appropriate percentage or calorie target.
Why the calculator does not convert the gap to weight
Body weight and composition change dynamically. As weight changes, energy expenditure and several metabolic processes also change, so a fixed conversion from accumulated calories to pounds or kilograms can overstate long-term outcomes.
The NIH Body Weight Planner uses a dynamic model and more personal inputs for adult planning. This simpler calculator is useful for checking arithmetic, not for replacing individualized assessment or forecasting a scale reading.
Frequently asked questions
▶How is a calorie deficit calculated?
Subtract planned average intake from estimated maintenance energy. For example, 2,400 minus 1,900 gives an entered deficit of 500 kcal/day.
▶What if intake is above maintenance?
The calculator reports a surplus instead of hiding the negative sign. Weekly and multiweek totals keep the same direction.
▶Does this predict how much weight I will lose?
No. It reports an energy gap between two estimates. It does not model metabolic adaptation, changes in activity, body composition, water or logging error.
▶Why can I not enter less than 1,000 kcal/day?
The NIH Body Weight Planner does not accept daily intake below 1,000 kcal because food-group and nutrient recommendations will not be met. That floor is not a personalized safe minimum.
▶Where do I get a maintenance estimate?
You can use a separate total-daily-energy estimate or a measured value. Treat either as uncertain and revise it using real observations and qualified guidance where appropriate.
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Open calculator →Disclaimer: Calorie Deficit Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.