The first numbers to know before any diet are your BMI and how many calories you burn a day. Skip them and crash-dieting just costs you muscle and invites the weight back. Enter height, weight, age and activity to get your BMI category, healthy weight range, basal metabolic rate and daily calorie needs at once.
Calculates automatically. BMI categories follow the Korean Society for the Study of Obesity (2022) guideline; BMR uses the Mifflin-St Jeor equation. This is a reference estimate that cannot account for muscle mass or body fat, and is not a medical diagnosis.
BMI categories (Korean guideline, 2022)
Koreans and other Asian populations carry more body fat at the same BMI than Western populations, so the cut-offs are lower than the WHO international standard.
- Under 18.5 — underweight
- 18.5 – 22.9 — normal
- 23 – 24.9 — pre-obesity (overweight)
- 25 – 29.9 — obesity class I
- 30 – 34.9 — obesity class II
- 35 and above — obesity class III
Check your waist too. Even with a normal BMI, 90cm or more for men and 85cm or more for women counts as abdominal obesity and warrants attention. Visceral fat predicts metabolic risk better than BMI alone.
BMR and daily calorie needs
- BMR — the calories burned just breathing and maintaining body temperature, even at complete rest.
- Daily needs (maintenance) — BMR multiplied by your activity level. Eat this much and weight holds steady.
- Weight-loss target — subtracting 500 kcal a day corresponds in theory to about 0.5 kg per week.
The crucial rule is not to eat below your BMR. Go under it and you lose muscle while metabolism drops, leaving a body that resists further loss. The calculator won't recommend going below 90% of BMR for that reason.
FAQ
I train hard but my BMI says obese.
Muscle weighs more than fat, so heavy training can push BMI up. In that case judge by body fat percentage and waist circumference instead.
My BMI is normal but my belly sticks out.
That may be "normal-weight obesity." With low muscle and high body fat, metabolic risk resembles obesity even at a normal weight. Always check waist circumference.
How do I pick an activity level?
Base it on exercise frequency, and when unsure choose one level lower — most people overestimate how active they are.
How fast is safe to lose weight?
0.5–1 kg per week is generally considered a sustainable pace. Faster raises the risk of muscle loss and regain.
Diets succeed less on how little you eat than on whether you cut while protecting your basal metabolism.
This calculator is a general reference estimate and does not replace medical diagnosis or treatment. If you have a health condition or are pregnant or nursing, consult a professional.
