Child Growth Percentile Calculator
Weight-for-age, length or height-for-age and head circumference percentiles and z-scores: WHO standards from birth to 2 years, CDC charts from 2 to 20.
Result…
How it's calculated
z = ((X ÷ M)^L − 1) ÷ (L × S), or ln(X ÷ M) ÷ S when L = 0 percentile = Φ(z) × 100 L, M, S for the sex and age, interpolated between the table rows: WHO (monthly, birth to 24 months) under 2 years, CDC 2000 (half-monthly, 2 to 20 years) from 2
Growth percentiles compare one measurement with children of the same sex and age. Following CDC's advice for the United States, this uses the WHO Child Growth Standards (2006) from birth to 2 years, built from healthy breastfed children in six countries, and the CDC 2000 growth charts from 2 to 20 years. Many countries use the WHO standards to age 5 and their own charts after that (the UK, for example, uses UK-WHO charts), so a percentile can differ from your child's health record. Head circumference is charted here to 2 years only. Under 2 the length is measured lying down; from 2 the height is measured standing, which reads slightly less.
Your numbers, step by step
About the Child Growth Percentile calculator
Parents often see a percentile in a baby's health record and wonder what it means. This calculator gives the weight-for-age, length or height-for-age and head circumference percentiles, with z-scores, for a child of a given sex and age. From birth to 2 years it uses the WHO Child Growth Standards (2006), which describe healthy breastfed children in six countries. From 2 to 20 it uses the CDC 2000 growth charts. That split follows CDC's advice for the United States. You can enter any one measurement or all three, in metric or imperial, and give the age in years and months or as two dates. The steps show the table values used for that exact age, how the z-score is worked out, and the measurements at the 3rd, 50th and 97th percentiles.
How to use it
- Choose “Boy” or “Girl” and give the age, either as years and months or as the “Date of birth” and “Date measured”.
- Pick metric or imperial under “Units”.
- Enter the “Weight”, the “Length or height” and, under 2 years, the “Head circumference”. Leave any field blank to skip it.
- Read each percentile and z-score, and check which chart was used.
Worked example
A boy aged 1 year 0 months weighs 9.6 kg (21.2 lb), is 76 cm (30 in) long and has a head circumference of 46 cm (18.1 in). The calculator uses 12.5 months and the WHO tables for boys. His weight is at about the 43.9th percentile (z = −0.15), his length at the 44.5th (z = −0.14) and his head circumference at the 43.7th (z = −0.16).
Updated
Questions people ask
How are growth percentiles calculated?
Each chart gives three numbers for every age: L, M (the median) and S. The z-score is ((X ÷ M)^L − 1) ÷ (L × S), where X is the measurement. The percentile is the share of the normal curve below that z-score.
What is a normal growth percentile for a baby?
Any percentile can be normal. A child at the 10th percentile can be as healthy as one at the 90th. What matters more is whether a child keeps roughly to their own curve over time.
Why does the chart change at 2 years?
CDC recommends the WHO standards from birth to 2 years and its own 2000 charts from 2 to 20. Under 2 the length is measured lying down. From 2 the height is measured standing, which reads slightly less.
Why is head circumference not shown after age 2?
This calculator charts head circumference with the WHO standards to 2 years only. The CDC charts for 2 to 20 years do not include it.
Does my country use the same charts?
Not always. Many countries use the WHO standards to age 5 and their own charts after that, and the UK uses UK-WHO charts. Your child's record may show a slightly different percentile.
Should I worry about a low or high percentile?
One reading says little on its own, and measuring errors are common. A doctor or health visitor looks at the pattern across several visits, so ask them if you are worried. For BMI from age 2, use the child BMI percentile calculator. The source tables are on the WHO Child Growth Standards site.