Weight Change Timeline Calculator
Body-weight change is estimated from stored energy: roughly 7,700 kcal is equivalent to 1 kg of body mass.
Enter Values
How to use this calculator
- Enter your current weight and your goal weight in kilograms.
- Enter the daily calorie deficit you plan to hold (positive to lose weight; put a minus sign in front to model a surplus for gaining).
- Read the time to reach your goal, the weekly rate, and your projected weight after 1, 2 and 4 weeks.
How it works
Body-weight change is estimated from stored energy: roughly 7,700 kcal is equivalent to 1 kg of body mass. The weight you need to change is |current − goal|, and the total energy is that many kilograms × 7,700 kcal. Dividing the total energy by your daily deficit gives the number of days, which is then expressed in weeks and days.
The weekly rate is deficit × 7 ÷ 7,700 kg per week, and the milestone weights subtract that rate for each elapsed week (capped once the goal is reached). The sign of the deficit must match the direction of change — a deficit loses weight, a surplus (entered as a negative deficit) gains it — otherwise the tool flags the mismatch. If the implied rate exceeds about 1 kg/week the result carries a caution, because faster changes are hard to sustain.
Worked example
Lose 10 kg on a 500 kcal/day deficit. Starting at 90 kg with a goal of 80 kg and a steady 500 kcal/day deficit: 10 kg × 7,700 = 77,000 kcal to burn. At 500 kcal/day that is 154 days, i.e. 22 weeks, losing about 0.45 kg/week. After 4 weeks you would be around 88.18 kg.
Common mistakes
- Confusing the daily deficit with your total daily intake. The deficit is how far below (or above) maintenance you eat, not the number of calories you eat — a 500 kcal deficit does not mean 500 calories of food.
- Expecting a perfectly linear result. The 7,700 kcal/kg rule is an average; real weight change slows as your body adapts and fluctuates day to day from water and food weight.
- Entering a surplus as a plain positive number when trying to gain weight. To gain, put a minus sign in front of the deficit (a negative deficit is a surplus); a positive deficit with a higher goal weight is flagged as going the wrong way.
Frequently asked questions
How long will it take to lose 10 kg?
It depends on your daily deficit. At a 500 kcal/day deficit, 10 kg takes about 154 days (22 weeks), losing roughly 0.45 kg/week. A larger deficit is faster but harder to sustain, and going much beyond about 1 kg/week is generally not recommended.
Where does the 7,700 number come from?
It is the widely used estimate that about 7,700 kcal of energy is stored in 1 kg of body fat/mass. It is an average rule of thumb, so use the timeline as a guide rather than a guarantee.
Can this tool model weight gain too?
Yes. Set your goal weight above your current weight and enter the deficit as a negative number (a negative deficit is a surplus). The tool then projects how long the gain takes at that surplus.
Is a bigger deficit always better?
No. Very large deficits are hard to maintain, can cost muscle, and may be unsafe. If your inputs imply more than about 1 kg/week the tool adds a caution and suggests a gentler, longer plan. It is an estimate, not medical advice.
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Cite this tool
Zerdly. (2026). Weight Change Timeline Calculator. Retrieved from https://www.zerdly.com/tools/weight-change-timeline-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.