Health calculator
BMI Calculator
Calculate Body Mass Index with metric or US units, then review category, health risk and estimated healthy weight range.
BMI category scale
UnderweightNormalOverweightObesity
Adult thresholds: underweight below 18.5, normal 18.5-24.9, overweight 25-29.9, obesity 30 or above.
BMI categories for adults age 20 and older
| BMI category | BMI range | Health risk |
|---|---|---|
| Underweight | 18.4 and below | Malnutrition risk |
| Normal weight | 18.5 - 24.9 | Low risk |
| Overweight | 25 - 29.9 | Enhanced risk |
| Moderately obese | 30 - 34.9 | Medium risk |
| Severely obese | 35 - 39.9 | High risk |
| Very severely obese | 40 and above | Very high risk |
BMI categories for kids and teens under age 20
| BMI category | BMI percentile | Health risk |
|---|---|---|
| Underweight | Less than 5th percentile | Malnutrition risk |
| Normal weight | 5th to under 85th percentile | Low risk |
| Overweight | 85th to under 95th percentile | Enhanced risk |
| Obesity | 95th percentile and greater | High risk |
This calculator shows adult categories. Pediatric BMI needs age-and-sex growth charts.
BMI formula
Metric: BMI = weight(kg) / height(m)².
US: BMI = 703 × weight(lb) / height(in)².
Healthy weight is estimated from BMI 18.5 to 24.9 at the entered height.
BMI calculator FAQ
Is BMI accurate for everyone?
No. It does not directly measure body fat and may be less informative for some people.
Why ask for age and sex?
People under 20 require percentile interpretation based on age and sex.
Does BMI replace medical advice?
No. Consult a qualified health professional for medical guidance.
What is a healthy adult BMI?
The commonly used adult normal range is 18.5 to 24.9.