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
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 |
| Severe obesity | At least 120% of the sex- and age-specific 95th percentile BMI, or BMI of 35 or above | Clinical review recommended |
For ages 2-19, this calculator uses CDC 2000 sex-specific BMI-for-age LMS data and age in completed years and months. Percentiles are screening results, not a diagnosis.
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.
Calculation method and sources
Adults use standard BMI thresholds. Ages 2-19 use sex-specific CDC 2000 BMI-for-age LMS parameters at the entered age in months. The calculator derives a z-score and percentile and compares BMI with the CDC 5th, 85th and 95th percentile values.
Authoritative references
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.
Handy Tool Lab
How this tool is maintained
Handy Tool Lab builds and tests each tool around repeatable examples. Formula-based tools use published references when a suitable source exists; browser utilities are checked with representative inputs and output cases.