How the calculation works
The calculator estimates the calories you need to keep your weight (Mifflin-St Jeor equation times your activity level) and sets your intake at the chosen deficit below that. Then it follows your weight week by week: each week the deficit is turned into kilograms, and the maintenance level is recalculated for the new, lower weight.
Intake = maintenance now − deficit
Weekly loss = (maintenance at that weight − intake) × 7 ÷ 7,700
About 7,700 calories correspond to 1 kg of body weight. Your intake stays the same every day, so the deficit shrinks as you get lighter.Worked example
Woman, 35, 165 cm, 80 kg, moderate activity, goal 70 kg, deficit 500.
- Maintenance is about 2,317 calories, so the intake is about 1,818 calories a day.
- In week 1 the loss is about 0.45 kg. After 12 weeks the weight is about 75 kg.
- The loss slows as maintenance falls, so reaching 70 kg takes about 27 weeks.
What this calculator does not include
- Water balance, muscle gain and changes in activity.
- A change in your intake over time, or days you eat more or less.
- Individual differences. Real progress is rarely a straight line.
Results are estimates for information, not medical advice. Last updated: 12 November 2026.
Frequently asked questions
Why does the estimate give a time and not a date?
Because real weight loss varies. Water, training, sleep and how closely you follow a plan all move the scale. Treat the time as a rough guide, not a promise.
Why does my weight loss slow down?
A lighter body uses less energy. As your weight falls, the calories you need to maintain it fall too, so the same intake gives a smaller deficit. The calculator recalculates this every week.
What does "Not reached at this intake" mean?
At that calorie intake your weight settles at a level above your goal, because your body then uses as much as you eat. Eat a little less or move more to go lower.
How big a deficit is sensible?
A deficit of 250 to 500 calories a day, or about 0.25 to 0.5 kg a week, is common advice. The calculator warns you when your intake falls below your resting energy. Talk to a doctor or dietitian before a bigger deficit.
Is this suitable for everyone?
No. It is for healthy adults aged 18 and over. It does not fit children, pregnancy, breastfeeding, medical conditions or a history of eating problems. Ask a doctor or dietitian for advice that fits you.