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 31, 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 applies a linear 7,700 kcal per kilogram rule of thumb to explore a weight-loss timeline. It is intentionally simpler than a physiological model. The NIH Body Weight Planner accounts for changes in energy needs and activity over time; this calculator does not.
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 |
The shortcut returns 140 days, or 20 weeks. At 500 calories per day it returns 154 days. These are outputs of a linear scenario, not predictions of when a person will reach the entered weight.
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 an educational scenario for adults, not medical or dietary advice. Real weight change is dynamic: energy needs adapt as weight and activity change, and the same nominal food reduction does not guarantee a fixed daily energy deficit. Water, lean tissue, medication, illness, pregnancy, breastfeeding, and many other factors can dominate a short-term scale trend. The calculator does not set a safe calorie intake or determine whether the goal weight is appropriate. It should not be used by children or during pregnancy or breastfeeding. Seek individualized advice before making a substantial change.
Sources and scope
- Jurisdiction
- General educational model for adults
- Data current to
- Formula has no current market or regulatory data
- Last updated
- About the Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases
- Eating and Physical Activity to Lose or Maintain Weight — National Institute of Diabetes and Digestive and Kidney Diseases
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.