A child growth percentile calculator based on CDC growth charts
This child growth percentile calculator shows where a child’s measurements sit compared with other children of the same age and sex. Enter the date of birth (or age), weight, length or height and, for children up to 36 months, head circumference, and it returns a percentile and a z-score for each measurement — plus BMI-for-age from 2 years and weight-for-length for babies — together with a growth curve chart marking the child’s point between the 3rd and 97th percentile lines. Save each check-up to the growth history and the chart becomes a baby growth chart over time, with the points joined.
The numbers come from the official CDC growth chart data files (LMS parameters from the US National Center for Health Statistics, 2000 charts with the revised BMI file), which are public domain and embedded in the page, so everything runs in your browser.
A percentile is a comparison, not a verdict: doctors look at how a child follows a curve over months. This tool is informational and not medical advice.
How to use the Child Growth Percentile Calculator
- Choose Boy or Girl — the charts differ.
- Enter the date of birth and the date measured, or switch to Age in years and months.
- Enter the weight, length/height and, under 3 years, the head circumference. Any one measurement is enough.
- For ages 24–36 months, choose whether the child was measured lying down (birth–36 month charts) or standing (2–20 year charts).
- Read the percentile and z-score for each measurement in the table, and pick which growth curve to display.
- Press Add this measurement after each check-up to build the growth history on the chart.
Child Growth Percentile Calculator features
Real CDC data, LMS method
Weight-, length-, head- and weight-for-length (birth to 36 months) and weight-, stature- and BMI-for-age (2 to 20 years), with L, M and S interpolated to the exact age.
Percentile curve chart
The 3rd to 97th percentile curves (nine lines) with the child’s point.
BMI category for 2–20 years
CDC weight-status bands, and above the 95th percentile the BMI as a percentage of the 95th percentile.
Growth history plot
Saved check-ups are drawn on the curves and joined, each with its percentile.
Metric or imperial, private
kg or lb, cm or inches. Nothing is uploaded; the history stays in this browser.
How percentiles and z-scores are calculated
For every age (or length) the CDC publishes three numbers: M, the median; S, the coefficient of variation; and L, a Box-Cox power that corrects for skew. A measurement X is turned into a z-score with z = ((X ÷ M)L − 1) ÷ (L × S), and the percentile is the share of a normal distribution below that z. The tool interpolates L, M and S linearly between the CDC’s half-month rows, using age in months = days ÷ 30.4375.
You can check it against the files: the CDC’s wtageinf.csv lists 4.446 kg as the 97th percentile for boys at birth, and this calculator returns the 97th (z = 1.88); statage.csv lists 151.1 cm as the 3rd percentile for girls at 20 years, and it agrees.
Reading the result
- Crossing lines matters more than the line itself. A child who moves steadily along the 10th percentile is usually growing well; one who drops from the 75th to the 25th deserves a check.
- Under 2 years, US guidance recommends the WHO growth standards; the CDC birth–36 month charts used here can differ, especially for breastfed babies.
- Premature babies are plotted by corrected age (age minus weeks born early) until about 2 years — work it out with the corrected age calculator and enter it as the age.
- Above the 97th or below the 3rd percentile the LMS curves are extrapolated, and the CDC’s 2022 extended BMI charts describe severe obesity as a percentage of the 95th percentile, which is shown in the result.
| Percentile | z-score | What it means |
|---|---|---|
| 3rd | −1.88 | 3 in 100 children of this age and sex are smaller |
| 15th | −1.04 | Below average but common |
| 50th | 0 | The median |
| 85th | +1.04 | BMI at or above this is “overweight” on CDC BMI-for-age |
| 97th | +1.88 | Only 3 in 100 are larger |
WHO and IAP charts
Many countries use the WHO Child Growth Standards (2006) for young children. WHO’s terms of use require written permission to reproduce substantial parts of its material, so its tables are not built in; compare with the official charts at who.int.
In India the Indian Academy of Pediatrics recommends the WHO standards under 5 years and its revised IAP 2015 charts for height, weight and BMI from 5 to 18 years (Indian Pediatrics 2015;52:47–55). Its BMI charts mark overweight and obesity at the 23 and 27 adult-equivalent lines, because Asian children carry more risk at a lower BMI. The LMS values are not openly published, so IAP percentiles are not computed here: use the charts at iapindia.org, or ask your paediatrician.
Measuring accurately
Weigh babies naked or in a dry nappy, older children in light clothes. Measure length lying down until 2 years and standing height after that. Head circumference is the largest measurement around the forehead and back of the head. For adults use the BMI calculator.
Child Growth Percentile Calculator FAQ
How do I calculate my child’s growth percentile?
Enter sex, age or date of birth and any measurement; the calculator compares them with the CDC growth charts and shows each percentile and z-score.
What does the 50th percentile mean?
The median: half of children of the same age and sex measure less. It is not a target — any steady percentile between roughly the 3rd and 97th can be normal.
Is a low percentile bad?
Not by itself — small parents often have small, healthy children. Doctors look for a value below the 3rd percentile, a big drop across lines, or weight falling behind height. Discuss any concern with your paediatrician.
Should I use WHO, CDC or IAP charts?
US guidance uses WHO standards up to age 2 and CDC charts from 2 to 20. In India, IAP recommends WHO standards under 5 and the IAP 2015 charts from 5 to 18. This tool uses CDC data throughout, so values can differ from WHO or IAP charts.
Is this a kids BMI calculator?
Yes. From 2 to 20 years, enter weight and height for the BMI-for-age percentile and CDC category: underweight below the 5th, healthy 5th to below 85th, overweight 85th to below 95th, obesity 95th or above.
What is a z-score?
The number of standard deviations from the median: 0 is the 50th percentile, −2 about the 2nd and +2 about the 98th. It is useful where percentiles bunch together.