BMI is a quick calculation using weight and height, but a child’s result cannot be interpreted like an adult’s. Children are still growing, so paediatricians compare BMI with age- and sex-specific growth charts and look at the pattern over time. Use this calculator to check the number, then discuss any concern with your child’s doctor rather than starting a restrictive diet.
Child and Teen BMI Calculator
Use the official CDC metric calculator below for ages 2–19. It calculates BMI and interprets it by age and sex. Results are a screening aid, not a diagnosis.
Open the CDC calculator in a new page if the embedded tool does not appear.
What is BMI?
Body mass index expresses weight relative to height in kilograms per square metre. It is inexpensive and useful for population monitoring and health screening. It does not directly measure body fat, muscle, bone, puberty, diet quality or fitness. Two children with the same BMI can have different builds and health needs.
For adults aged 20 and over, fixed BMI categories are often used as a screening starting point. Those adult cut-offs must not be applied directly to a five-year-old, ten-year-old or teenager.
Why children need BMI-for-age charts
A child’s body composition changes with normal growth. The same raw BMI can mean different things at different ages, and expected patterns also differ by sex. Clinicians therefore use BMI-for-age percentiles or z-scores from an appropriate reference, along with height, weight, development, family history and clinical assessment.
The CDC child calculator covers ages 2–19 and describes BMI as a screening measure, not a diagnosis. WHO provides growth standards for children under five and a growth reference for ages 5–19. Indian paediatricians may use growth charts recommended for Indian children, so bring the measurements to your own doctor rather than comparing results from several websites.
How to measure height and weight accurately
- Use a level digital scale on a hard floor, not carpet.
- Measure at a similar time of day in light clothing and without shoes.
- For standing height, place heels together, legs straight, shoulders relaxed and head looking forward.
- Keep heels, and where possible the back, against a flat wall. Place a rigid book level on the head and mark the wall.
- Record height to the nearest 0.1 cm if practical and weight to the nearest 0.1 kg.
- Do not repeatedly weigh a child out of anxiety. Growth is assessed over sensible intervals.
What should parents do with the result?
A single number is not a reason to praise, criticise or frighten a child. Save the date and measurements, then ask the paediatrician to plot them correctly. A clinician may repeat the measurement, review the growth curve, examine the child, discuss sleep, movement and eating, and order tests only when indicated.
Avoid discussing “good” and “bad” bodies or putting a child on a weight-loss plan without medical guidance. Weight stigma can harm wellbeing and may discourage children from seeking help. Talk instead about energy, strength, sleep, enjoyable movement and varied food.
Healthy habits for the whole family
- Offer regular meals and snacks with vegetables, fruit, pulses, grains, dairy or suitable alternatives and other protein sources.
- Keep water easily available and limit sugary drinks.
- Let children respond to hunger and fullness; avoid forcing a clean plate.
- Build daily active play into family life and reduce long uninterrupted sitting.
- Protect age-appropriate sleep and predictable routines.
- Make changes as a household so one child is not singled out.
When to speak with a paediatrician
Book a review if weight or height changes rapidly, the child crosses growth-chart lines, has poor appetite or persistent fatigue, snores heavily, has excessive thirst or urination, develops early or delayed puberty concerns, takes medicines affecting growth, or you are worried for any reason. Seek prompt help for fainting, severe weakness, dehydration, breathing difficulty or signs of an eating disorder.
Frequently asked questions
What is a healthy BMI for a child?
There is no single healthy number for every child. BMI must be interpreted by exact age and sex on an appropriate growth chart and alongside the overall growth pattern.
Can I use adult BMI categories for a teenager?
Not until age 20 in the CDC system. Children and teenagers need BMI-for-age interpretation.
Is BMI an accurate measure of body fat?
No. It is a screening calculation and does not directly measure fat, muscle or bone.
How often should I weigh my child?
Routine growth checks at healthcare visits are usually sufficient unless a clinician recommends more frequent monitoring.
Should a child diet if BMI is high?
Do not start a restrictive diet without a paediatric assessment. Family-wide food, activity and sleep habits are safer starting points.
Does a low BMI always mean poor nutrition?
No. Build, genetics, measurement error and medical factors all matter. A clinician should review the child’s curve and health.
Reliable sources
This tool and article provide general information only. They do not diagnose a health condition or replace a paediatric growth assessment.
