Weight Loss Timeline Calculator
Estimate how long it will take to reach your goal weight with a daily calorie deficit.
How to use this tool
- Enter current weight, goal weight and daily calorie deficit in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your estimated weeks and the full breakdown beneath it.
1 kg of body fat contains roughly 7,700 kcal. Divide your total fat to lose by your daily deficit to estimate time to goal.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
Weight to lose (kg) = current weight − goal weight
Days required = (kg to lose × 7700) ÷ daily calorie deficit
Weeks required = days ÷ 7
How it works
The calculator uses the widely cited rule of thumb that 1 kg of body fat contains approximately 7700 kcal, so the total calorie deficit needed equals kilograms to lose multiplied by 7700. Dividing by the daily deficit gives the number of days, which is then converted to weeks. This is a linear estimate; in practice weight loss slows as body weight decreases (reducing TDEE), so actual timelines are often longer than the estimate, particularly for larger losses.
Worked example
- Current weight = 85 kg, Goal = 75 kg, Daily deficit = 500 kcal/day.
- Weight to lose = 85 − 75 = 10 kg.
- Total deficit needed = 10 × 7700 = 77 000 kcal.
- Days = 77 000 ÷ 500 = 154 days.
- Weeks = 154 ÷ 7 = 22 weeks.
Estimated time: 22 weeks to lose 10 kg
Common mistakes to avoid
- Using 3,500 kcal per pound (the older US estimate) instead of 7,700 kcal per kg, which causes unit-mixing errors if weight is entered in kilograms.
- Ignoring metabolic adaptation: as body weight decreases, TDEE also decreases, so the same calorie deficit produces slower loss over time than a linear calculation suggests.
- Setting an aggressive deficit (e.g. 1,000+ kcal/day) and trusting the timeline without accounting for increased hunger, muscle loss, or adherence issues at large deficits.
Key terms
- Calorie deficit
- The gap between calories consumed and calories burned; a sustained deficit causes the body to draw on stored fat for energy.
- 7700 kcal/kg rule
- An approximation that 1 kg of body fat stores roughly 7700 kcal of energy, used to estimate how large a deficit is needed to lose a given mass.
- TDEE (Total Daily Energy Expenditure)
- The total calories burned per day including basal metabolism, physical activity, and digestion.
- Linear weight loss model
- A simplified model assuming a constant rate of loss; real weight loss is non-linear because metabolism adapts to lower body weight over time.
- Plateau
- A period during a diet where weight loss stalls, often because reduced body mass lowers TDEE, closing the effective calorie deficit.
Frequently asked questions
- How many calories are in a kilogram of fat?
- Approximately 7,700 kcal per kg. Some sources use 7,000–7,700; this calculator uses 7,700.
- Is a 500 kcal/day deficit safe?
- A 500 kcal deficit typically produces about 0.5 kg of loss per week, which is within the NHS and WHO recommended range of 0.5–1 kg per week.