Growth Charts for Children: How the CDC and WHO BMI-for-Age Charts Work
A child's weight on its own says little: what matters is how their body mass index compares with other children of the same age and sex, and how it changes as they grow. That comparison is made on growth charts. This page explains which charts the CDC and the WHO publish, which one applies at which age, how to read a BMI-for-age curve, and where to find the official calculators that do the arithmetic for you.
General information, not medical advice. A single measurement does not diagnose anything: a doctor, school nurse or health visitor reads growth charts alongside how the child is growing over time.
Which chart for which age
| Age | Chart | Published by |
|---|---|---|
| Birth to 2 years (US) | WHO growth standards, as recommended by the CDC | WHO, adopted by the CDC |
| 2 to 19 years (US) | CDC growth charts, including BMI-for-age | CDC, National Center for Health Statistics |
| 2 to 19 years, very high BMI (US) | CDC extended BMI-for-age growth charts | CDC |
| Birth to 5 years (international) | WHO Child Growth Standards, including BMI-for-age | WHO |
| 5 to 19 years (international) | WHO Growth Reference 2007, BMI-for-age | WHO |
| 2 to 18 years (UK) | UK-WHO growth charts, with a BMI centile lookup | Royal College of Paediatrics and Child Health (RCPCH) |
The CDC's advice is simple: WHO growth standards for infants and children up to age 2, CDC growth charts for children aged 2 and older, and the extended BMI-for-age charts for children with severe obesity. It also stresses that growth charts are not meant to be used as a diagnostic tool on their own; they contribute to an overall picture of the child's health.
Standards and references: why there are two families of charts
The WHO Child Growth Standards, released in 2006, describe how children aged 0 to 59 months grow in conditions that support healthy growth, using data from children in six countries, including the United States. In the CDC's words, they show how young children grow under those conditions rather than how they happen to grow in environments that may not support optimal growth. That is why they are called a standard.
The WHO Growth Reference 2007 for 5 to 19 year olds is a reconstruction of the 1977 US National Center for Health Statistics reference, supplemented with data from the sample used for the under-fives standards and built with the same statistical method. The CDC growth charts released in 2000 describe US children, mostly measured between 1963 and 1980. They do not go beyond the 97th percentile, which is why the CDC added extended BMI-for-age percentiles in 2022, based on data that include children with obesity measured up to 2016.
How to read a BMI-for-age chart
- Axes. Age runs along the bottom, BMI up the side. There is one chart for girls and one for boys, because body fat changes differently with age in each.
- Curves. Each curve is a percentile, including the 5th, 85th and 95th that mark the CDC category boundaries. A point on the 85th percentile curve means the child's BMI is higher than that of 85% of children of the same sex and age in the reference data.
- Shape. The curves are not flat. BMI usually falls after infancy, reaches a low point in early childhood and then rises again through the school years and adolescence. That is why the same BMI can be high at one age and ordinary at another.
- Several points. Health professionals look at measurements taken over time. A child who follows roughly the same curve is growing along their own path; a marked change in direction is something to discuss with them, not a verdict.
Percentiles and z-scores
The CDC expresses a child's position as a percentile: below the 5th is underweight, the 5th to below the 85th is a healthy weight, the 85th to below the 95th is overweight and the 95th or above is obesity. The categories are set out in our guide to BMI for children and teens.
The WHO uses standard deviations, also called z-scores: the distance from the median of the reference, in units of its spread. For 5 to 19 year olds, overweight is a BMI-for-age more than 1 standard deviation above the median and obesity more than 2 above it. For children under 5, the WHO uses weight-for-height instead: overweight is more than 2 standard deviations above the median of the Child Growth Standards and obesity more than 3.
The two scales can be translated: a z-score of +1 sits at about the 84th percentile and +2 at about the 97.7th. So the WHO's overweight cut-off for school-age children is close to the CDC's 85th percentile, while its obesity cut-off (+2) is stricter than the CDC's 95th percentile. Different tools can therefore describe the same child slightly differently; use the one your own health service uses.
Why we do not calculate percentiles on this site
Each chart is built from three parameters published for every month of age and for each sex, known as L, M and S (for the skew, median and spread of the reference). The CDC and the WHO publish these tables, and turning a child's BMI into a percentile with them is precise work: the age has to be exact to the month, the right table has to be used for the age, and since 2022 the CDC computes percentiles above the 95th with its extended method. Rather than risk a small error on a sensitive subject, our calculator sends anyone under 18 to the official tools below, which apply the published tables and explain the result.
Official calculators and charts
- CDC Child and Teen BMI Calculator: ages 2 through 19; gives the BMI, the BMI percentile and the category, and plots the result on a growth chart. US customary or metric units.
- NHS BMI calculator for children and teenagers: ages 2 to 17, for families in the UK.
- CDC growth charts: the clinical charts to print, the WHO charts for US children under 2 and the extended BMI-for-age charts.
- WHO Child Growth Standards (birth to 5 years) and WHO growth reference data for 5 to 19 years, with charts and tables for girls and boys; the WHO also offers its AnthroPlus software for health workers.
- UK-WHO growth charts for 2 to 18 years, from the Royal College of Paediatrics and Child Health, used by health professionals in the UK.
For adults, the measures are different: see the healthy weight chart for adults and adult BMI categories.
Sources
- Centers for Disease Control and Prevention, National Center for Health Statistics, "Growth Charts", "WHO growth standards for use in US infants and children birth to 2 years", "CDC Extended BMI-for-age Growth Charts" and data files with LMS parameters (pages last reviewed 2 September 2024).
- CDC, "Child and Teen BMI Categories".
- World Health Organization, "Obesity and overweight" fact sheet: definitions for children under 5 and aged 5 to 19.
- WHO, "Growth reference data for 5-19 years": the 2007 reference and how it was built.
- Royal College of Paediatrics and Child Health, "UK-WHO growth charts - 2-18 years".
- Sources checked on 13 November 2026. The z-score to percentile equivalents (+1 ≈ 84th, +2 ≈ 97.7th) follow from the normal distribution.
Healthy weight & BMIBMI for children and teens
Children are still growing, so their BMI is compared with others of the same age and sex. How percentiles work and which official calculators to use.
Healthy weight & BMIAdult BMI categories explained
Underweight, healthy weight, overweight and the three obesity classes, the lower NICE thresholds for some ethnic groups, and how to read your number.
Healthy weight & BMIWhat is a healthy weight?
Why health services use BMI to describe a healthy weight, what it misses, which other measures help and what affects weight beyond food and exercise.