What is BMI for children and teenagers?
For adults, BMI is compared with fixed cut-offs such as 18.5 and 25. Children are different: their body fat changes naturally as they grow, and boys and girls develop differently. So a child’s BMI is compared with other children of the same age and sex using growth charts. The result is a BMI-for-age percentile.
For example, if a 10-year-old girl is at the 70th percentile, her BMI is higher than 70% of girls her age. This child BMI calculator uses the official U.S. Centers for Disease Control and Prevention (CDC) BMI-for-age growth charts for ages 2 to 19, which are widely used by paediatricians in the UAE, Pakistan and around the world.
How the child BMI calculator works
- It calculates BMI the usual way: weight (kg) ÷ height (m)².
- It finds the CDC reference values (called L, M and S) for your child’s exact age in months and sex.
- It converts the BMI into a z-score with the LMS formula — z = ((BMI ÷ M)L − 1) ÷ (L × S) — and then into a percentile.
Example: a 10-year-old boy who is 140 cm tall and weighs 38 kg has a BMI of 19.4. That places him at about the 85th percentile — the border between healthy weight and overweight for his age.
BMI percentile chart for kids: low, normal and high
| BMI-for-age percentile | Weight category | Level |
|---|---|---|
| Below the 5th percentile | Underweight | Low |
| 5th to below the 85th percentile | Healthy weight | Normal |
| 85th to below the 95th percentile | Overweight | High |
| 95th percentile or above | Obesity | Very high |
| 120% of the 95th percentile or above | Severe obesity | Very high |
Benefits of checking your child’s BMI
- Early detection: spotting a trend early makes it much easier to change habits gently.
- Healthy growth tracking over months and years, alongside your paediatrician’s growth charts.
- Prevents long-term problems: childhood obesity is linked with type 2 diabetes, high blood pressure, fatty liver, joint pain and low self-esteem.
- Reassurance: many parents worry needlessly — a healthy percentile confirms your child is growing well.
Health warnings
- Never put a child on a weight-loss diet without medical advice. Growing children need energy and nutrients.
- BMI percentile is a screening tool, not a diagnosis. Very muscular or early-maturing children may show a higher BMI.
- Avoid talking about weight or “fat” with your child; focus on health, energy and strong bodies.
- Sudden weight loss or gain, tiredness, excessive thirst or changes in eating behaviour need a doctor’s review.
- Not for babies under 2 — they use WHO weight-for-length charts.
Healthy habits for the whole family
Eat together, offer fruit and vegetables at every meal, swap sugary drinks and juice for water and milk, limit fast food and packaged snacks, and keep screen time under 2 hours a day. Children aged 5–17 need at least 60 minutes of active play every day. Our guides on childhood obesity, junk food and children’s health and nutrition for teenagers have more ideas.
Frequently asked questions
What is a healthy BMI percentile for a child?
A BMI between the 5th and 85th percentile for age and sex is considered a healthy weight. Below the 5th is underweight, the 85th to 95th is overweight and the 95th or above is obesity.
Why can’t I use the adult BMI calculator for my child?
Children’s body fat changes as they grow and differs between boys and girls, so a single cut-off does not work. Their BMI must be compared with growth charts for their age and sex.
At what age can I use this calculator?
This calculator works from 2 years to 19 years 11 months. For babies under 2, doctors use WHO weight-for-length charts.
My child is in the overweight range — what should I do?
Do not start a diet. Talk to your paediatrician, and make small family-wide changes: more vegetables, fewer sugary drinks and snacks, regular meals, more active play and good sleep.
Which growth charts does this calculator use?
It uses the CDC 2000 BMI-for-age growth charts and their official LMS reference values, which are also used by many doctors outside the United States.
Sources
- Centers for Disease Control and Prevention. CDC growth charts: BMI-for-age, 2 to 20 years (LMS parameters, bmiagerev). 2000.
- Kuczmarski RJ, et al. 2000 CDC Growth Charts for the United States: methods and development. Vital Health Stat 11(246), 2002.
- Hampl SE, et al. Clinical Practice Guideline for the Evaluation and Treatment of Children and Adolescents With Obesity. Pediatrics 2023.