Weight Loss Calculator
How long to reach your goal weight at a given calorie deficit.
Calories below maintenance each day. A 500 kcal/day deficit is a common, sustainable target.
Estimated time to goal
- Target date
- December 24, 2026
- Days to goal
- 154
- Weight to lose
- 10 kg
- Total calorie deficit
- 77,000 kcal
Estimate based on roughly 7,700 kcal per kilogram (3,500 per pound). A sustained daily deficit assumes a steady rate of loss; real progress varies and usually slows as you go. Not medical advice.
How the weight-loss timeline works
This tool estimates how long it will take to reach a goal weight from a steady daily calorie deficit. It rests on a single energy-balance idea: a kilogram of body weight stores about 7,700 calories (roughly 3,500 calories per pound). To lose weight you have to run a calorie deficit, eating fewer calories than you burn, and the total deficit you accumulate determines how much weight comes off.
The math is three short steps:
- Weight to lose:
currentWeight − goalWeight - Total deficit needed:
weightToLose × 7,700calories - Days to goal:
totalDeficit ÷ dailyDeficit
Weeks are simply the days divided by seven, and the target date counts that many calendar days forward from today. The calculator guards the inputs so it never returns a nonsense answer: your goal must be below your current weight, and the daily deficit must be greater than zero, because it is the divisor in the final step.
Worked example
Suppose you weigh 90 kg, want to reach 80 kg, and plan to hold a 550 calorie daily deficit.
| Step | Calculation | Result |
|---|---|---|
| Weight to lose | 90 − 80 | 10 kg |
| Total deficit needed | 10 × 7,700 | 77,000 kcal |
| Days to goal | 77,000 ÷ 550 | 140 days |
| Weeks to goal | 140 ÷ 7 | 20 weeks |
So a 10 kg loss at 550 calories a day takes about 140 days, or 20 weeks. Tighten the deficit to 500 calories a day and the same 10 kg takes 154 days (77,000 ÷ 500), a little over 22 weeks. The relationship is linear: cut the daily deficit in half and the time doubles, because you are chipping away at the same total with smaller daily bites.
How to use it
- Pick your units (kilograms or pounds) so the weight fields match how you weigh yourself.
- Enter your current and goal weight. The goal must be lower than where you are now.
- Enter a daily calorie deficit. This is how many calories below maintenance you eat each day. If you do not know your maintenance level, estimate it first with a daily-calorie tool, then subtract your planned deficit.
- Read the timeline. You get the number of weeks, the whole days to goal, and a projected target date counted forward from today.
- Re-run it monthly. As you lose weight your maintenance calories fall, so update your current weight every few weeks to keep the estimate honest.
Limitations
This is a planning estimate, not medical or dietary advice. The 7,700 calories per kilogram figure is an average, and real bodies do not lose weight in a perfectly straight line. Your maintenance calories drop as you get lighter, which shrinks a fixed-food deficit over time, so the later weeks usually run slower than the math suggests. Water retention, muscle gain from training, hormones, sleep, medication, and ordinary daily fluctuations can all move the scale by more than a day-to-day deficit would explain. Very aggressive deficits can cost muscle and are hard to sustain. Use the result to set a realistic target and to compare scenarios, and speak to a doctor or registered dietitian before starting a significant weight-loss plan.
Frequently asked questions
Where does the 7,700 calories per kilogram figure come from?
It is the long-standing rule of thumb for the energy stored in a kilogram of body fat, which works out to roughly 3,500 calories per pound. The calculator multiplies the weight you want to lose by 7,700 to get the total calorie deficit you need, then divides by your daily deficit to get the number of days. It is an approximation, not a fixed biological constant, so treat the timeline as a planning guide rather than a promise.
Is a 500 calorie per day deficit safe?
For many adults a deficit of about 500 calories a day produces a steady loss of roughly half a kilogram (one pound) a week, which is widely considered a sustainable pace. Larger deficits lose weight faster but are harder to maintain and can cost muscle. The right number depends on your size, activity, and health, so check with a doctor or dietitian before setting an aggressive target.
Why does my real weight loss slow down over time?
This model assumes a constant deficit and a constant rate of loss, but in practice your maintenance calories fall as you get lighter, so the same diet creates a smaller deficit over time. Water weight, muscle changes, and day-to-day fluctuations also blur the trend. Expect the early weeks to look faster than the math and the later weeks to look slower, and re-run the numbers with your new weight every month or so.
Does the calculator handle pounds as well as kilograms?
Yes. Switch the unit selector to imperial and enter your weights in pounds. Internally the tool converts pounds to kilograms using the exact factor 1 lb = 0.45359237 kg, runs the same calorie math, and converts the result back, so the energy figure of 7,700 per kilogram (about 3,500 per pound) is applied consistently either way.
What date does the timeline use as the start?
It counts forward from today using real calendar days, so months of different lengths and leap years are handled correctly rather than assuming every month is 30 days. The target date is the day your goal would be reached if you held the deficit every single day with no breaks.