BMI Weight Loss Calculator — Target Weight & Timeline
Enter your current weight, height, and a target BMI to see exactly how many kilograms to lose — and how many weeks it will take at a 250, 500, or 750 kcal/day calorie deficit.
kg
cm
To reach BMI 22
- 1
Height in metres
170 ÷ 100 = 1.7 - 2
Current BMI
85 ÷ 2.89 = 29.4 - 3
Target weight
22 × 2.89 = 63.6Weight that produces your target BMI at this height. - 4
Weight to lose
85 − 63.6 = 21.4
How does this calculator work?
Target weight = Target BMI × height (m)². Divide the difference between your current and target weight by the daily calorie deficit (in kcal) and multiply by 7 700 kcal/kg to get the number of days. A 500 kcal/day deficit loses about 0.45 kg/week — the most commonly recommended pace for safe weight loss.
Formula
How this is calculated
The calculator first works out your current BMI from weight and height (BMI = kg ÷ m²), then rearranges the same formula to find the weight that would produce your target BMI for the same height: target weight = target BMI × height². The difference between your current weight and that target weight is the total amount to lose (or gain, if your target BMI is above your current BMI).
To estimate timelines, the calculator uses the commonly cited clinical approximation that one kilogram of body fat stores roughly 7 700 kilocalories. Dividing the total fat-equivalent energy by a daily calorie deficit gives the number of days to reach the target, which is then converted to weeks. The three deficits shown — 250, 500, and 750 kcal/day — span a conservative to moderate rate; 500 kcal/day is the most commonly recommended deficit in clinical weight-management guidelines, corresponding to roughly 0.45 kg (1 lb) per week.
These are idealized estimates. In practice, weight loss is not linear — metabolic adaptation, water retention, and changes in lean mass mean real results differ from the formula. The 7 700 kcal/kg figure is an average for adipose tissue; actual results vary by individual. Use these numbers as planning benchmarks, not guarantees, and consult a doctor or dietitian for personalised guidance.
Frequently asked questions
Rearrange the BMI formula: target weight = target BMI × height (m)². Subtract that from your current weight to get the amount to lose. For example, at 170 cm (1.7 m) a target BMI of 22 gives 22 × 1.7² = 63.5 kg; if you currently weigh 85 kg you need to lose 21.5 kg.
A 500 kcal/day deficit is the most widely recommended starting point, targeting roughly 0.45 kg/week. Larger deficits lose weight faster but are harder to sustain and risk losing more lean muscle; smaller deficits are sustainable but slower. Most guidelines cap safe calorie restriction at about 750–1 000 kcal/day below maintenance.
A BMI of 22 sits near the middle of the 18.5–24.9 healthy range for adults. Any value within that range is medically acceptable; the right target for you depends on factors like muscle mass, age, and personal health goals. A doctor or registered dietitian can help set a realistic and appropriate goal.
Also known as
TG we-Calculate Editorial Team. (2026). BMI Weight Loss Calculator — Target Weight & Timeline [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/bmi-weight-loss-calculator
TG we-Calculate Editorial Team. "BMI Weight Loss Calculator — Target Weight & Timeline." TG we-Calculate. 2026. https://we-calculate.com/calculator/bmi-weight-loss-calculator.
TG we-Calculate Editorial Team, "BMI Weight Loss Calculator — Target Weight & Timeline," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/bmi-weight-loss-calculator
@misc{wecalculate_bmi_weight_loss_calculator, title = {BMI Weight Loss Calculator — Target Weight & Timeline}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/bmi-weight-loss-calculator}}, year = {2026}, note = {TG we-Calculate} }
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