A Calorie Deficit Calculator
A calorie deficit is subtraction: maintenance calories minus the calories you eat. The arithmetic is simple, but the figure you subtract from is a moving estimate rather than a fixed constant, and that is where most of the difficulty lives.
Daily deficit
500
- Deficit over a week
- 3,500
- Pounds the model predicts over that span
- 4.2857
- The same figure in kilograms
- 1.944
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
Daily deficit = maintenance calories - intake calories
- M
- Maintenance calories, the total daily energy expenditure that holds weight steady
- I
- Calories eaten each day
- D
- Daily deficit, positive when intake sits below maintenance
- 3500
- Approximate kilocalories per pound of body fat, the model's conversion constant
How to check the result by hand
- 1
Estimate your maintenance calories
Maintenance is your total daily energy expenditure, which you can estimate from a formula such as Mifflin-St Jeor or from a period of tracking. The estimate carries uncertainty of a few hundred calories either way. Treat it as a starting figure rather than a fixed truth, because it changes as your weight changes.
- 2
Subtract planned intake to get the daily deficit
2400 minus 1900 leaves 500 kcal a day. If the result is zero or negative there is no deficit, and the rest of the calculation has nothing to work with. The sign of this number is the whole premise of the exercise.
- 3
Convert to a weekly figure
Multiply by seven: 500 x 7 = 3500 kcal. This weekly total is the quantity the weight-change approximation actually consumes, and it is easier to sanity-check than a monthly figure. A deficit that varies from day to day should be averaged before you multiply.
- 4
Apply the 3500 kcal per pound approximation
Divide the total deficit by 3500 for pounds, or by 7700 for kilograms. Thirty days at 500 a day gives 500 x 30 / 3500 = 4.2857142857 pounds. The division is exact arithmetic on an approximate constant, so the precision of the output exceeds the precision of the input.
- 5
Convert if needed and label the answer an estimate
4.2857142857 pounds is 1.9439673 kilograms. Re-check the figure every few weeks against real weight, because the model's assumption of constant maintenance weakens over time. A growing gap between prediction and reality is the signal to re-estimate maintenance.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate A Calorie Deficit page.