By Zencalcy Editorial TeamLast reviewed About us
A calorie deficit is the gap between the energy you consume and the energy you expend. This calculator converts that gap into an estimated timeline for reaching a target weight, using the common approximation that one kilogram of fat stores about 7700 kilocalories. It works for loss or gain, and it shows the assumptions behind the estimate.
Estimate how long a daily calorie deficit will take to change your weight.
| Between 100 and 1500 kcal. |
Weight change (kg) = |current - target| Weeks = weight change x 7700 / daily deficit / 7
The 7700 kcal per kilogram figure is an approximation for fat tissue, not a law of physiology. Early weight loss often includes water and glycogen, and later loss slows as body mass falls. The estimate assumes the deficit stays constant, which rarely happens without adjustment.
| Symbol | Meaning |
|---|---|
| current | Current body weight in kilograms. |
| target | Goal body weight in kilograms. |
| deficit | Daily calorie deficit in kilocalories. |
| weeks | Estimated weeks to reach the target at a constant deficit. |
The change is 10 kg, so the estimated energy gap is 10 x 7700 = 77,000 kcal. At 500 kcal per day that is 154 days, or 154 / 7 = 22 weeks. Real progress may be faster at first because of water loss and slower later as maintenance calories fall.
The arithmetic assumes a fixed daily deficit and a fixed energy density for the weight you lose. Neither is fully true. Early in a diet, glycogen depletion releases water, so the scale can drop faster than fat loss alone would explain. Later, a lower body mass means a lower maintenance requirement, and adaptive thermogenesis can reduce expenditure further. Social and behavioural factors matter too: weekends, holidays and hunger often make the real deficit smaller than the planned one. A better use of this calculator is to set an order of magnitude. If the projection says 22 weeks, plan review points at four and eight weeks rather than expecting a straight line. Adjust based on the average trend, protect protein intake and strength training, and treat a plateau as information rather than failure.
Continue with the BMR Calculator (Mifflin-St Jeor), Harris-Benedict Calculator, or the Katch-McArdle Calculator — or browse more dietary tools and all health calculators.
Also see the Calorie Calculator, TDEE Calculator and the Macro Calculator.
No. It is a widely used approximation for the energy stored in a kilogram of fat tissue. Real weight change includes water, glycogen, lean mass and digestive contents, so the scale will not follow the projection perfectly.
Energy and nutrient estimates are population guidance, not personal prescriptions. Actual needs vary with body composition, medical conditions, medication, pregnancy and activity. Values are rounded and should be discussed with a registered dietitian or clinician when used to plan treatment.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026