Weight Loss Calculator
Daily calorie deficit, weekly loss rate, and pace verdict from current weight, goal, and weeks.
What it does
Weight loss planning works backwards from the goal: kilos to lose set the total energy debt, weeks set the daily pace. One kilo of body fat stores near 7,700 kcal, so 5 kg over 8 weeks asks about 688 kcal a day under maintenance.
The tool above takes current weight, goal weight, and weeks in metric or imperial. It returns the daily deficit with the weekly rate and a pace verdict beside them.
The default of 90 to 85 kg in 8 weeks needs 688 kcal/day at 0.63 kg/week: steady. The imperial mirror of 198 to 187 lb needs 686 kcal/day at 1.37 lb/week, the same trip in pounds.
The ranges follow CDC gradual loss guidance with the NIH body weight planner matching the slowdown warning. Both place 1 to 2 lb a week as the keepable pace and note that metabolism adapts below the simple math.
How to use
- Pick kilos or pounds for both weights.
- Enter current morning weight and the goal weight.
- Enter the weeks allowed for the trip.
- Read the daily deficit first for meal planning.
- Read the verdict: stretch the timeline when it reads brisk.
Formula
- 7,700
- Kcal stored per kilo of body fat (about 3,500 per pound).
- weeks
- Timeline spreading the total debt.
- 1-2 lb
- Weekly guide band for keepable loss.
Imperial converts to kilos first (x 0.45359237), then runs one path, so systems agree. The 7,700 rule overpromises late in long diets as expenditure adapts, which the verdict flags on fast plans.
Worked example
Example: 90 to 85 kg in 8 weeks
Metric defaults: current 90 kg, goal 85 kg, 8 weeks.
- Loss: 90 - 85 = 5 kg.
- Weekly: 5 / 8 = 0.63 kg/week.
- Total debt: 5 x 7,700 = 38,500 kcal.
- Daily: 38,500 / 8 / 7 = 688 kcal/day.
- Tool shows 688 kcal/day, 0.63 kg/week, steady verdict.
Reference table
| Trip | Daily deficit | Rate |
|---|---|---|
| 5 kg in 8 weeks | 688 kcal/day | 0.63 kg/week |
| 5 kg in 10 weeks | 550 kcal/day | 0.5 kg/week |
| 20 lb in 10 weeks | 998 kcal/day | 2 lb/week |
Limits
- Estimates only, not medical advice; conditions change safe rates.
- Simple math ignores adaptation that slows long diets.
- Exercise and protein shift what the lost kilos are made of.
- Very low intakes need clinician supervision.
Common mistakes
- Chasing the deadline instead of the deficit.
- Eating back every tracked exercise calorie.
- Weighing once after salty meals and quitting.
- Cutting protein with calories and losing muscle.
- Holding the same deficit for months without rechecking.
Try it yourself
Quick checks. Answers sit tucked under each question.
70 to 65 kg in 10 weeks?
5 kg at 550 kcal/day, 0.5 kg/week: steady.
Goal above current?
Rejected: goal must sit below current weight for a loss plan.
Why 1 to 2 lb a week?
Gradual losers keep weight off more often than fast losers, per CDC follow up data.
Questions
How much deficit to lose 1 kg a week?
About 1,100 kcal a day (7,700 / 7). Most do better near half that pace.
Why did loss stall at week six?
Adaptation: lighter bodies burn less and move less. Recheck intake and steps, then adjust.
Exercise or diet first?
Diet sets the deficit; training keeps muscle and mood. Both beats either alone.
Is 1,000 kcal a day safe?
Only under supervision. Moderate deficits near 500 to 750 suit most adults.
Does muscle loss matter?
Yes. Protein near target plus resistance work keeps the loss mostly fat.
What if the verdict reads brisk?
Add weeks. The same goal slower needs a smaller daily cut and keeps better.