Baby Growth Percentile Calculator (WHO, 0–2 years)
Find a baby’s weight, length and head circumference percentiles, and weight-for-length, from the WHO growth charts that CDC recommends for children under 2. Enter age, sex and measurements in metric or US units.
How to Use
- Give the baby’s age as months and days, or as the birth date and the date of the measurement (left blank, the measurement date is today).
- Pick boy or girl: the WHO charts are separate for each.
- Enter whatever was measured on that day: weight (kg, lb, or pounds and ounces like 7 lb 8 oz), length lying down (cm or inches) and head circumference.
- Choose the chart to show at the top. The readouts give that chart’s percentile, z-score and the 50th-percentile value; the table lists every chart your numbers allow.
- The growth chart draws the 2nd, 10th, 50th, 90th and 98th percentile curves with your baby marked, and Show Work lists the WHO L, M and S values used.
Worked Example
A boy at exactly 6 months, 7.9 kg. The WHO weight-for-age row for boys at 6 months gives L = 0.1257, M = 7.934 kg and S = 0.10958. Then z = ((7.9 ÷ 7.934)^0.1257 − 1) ÷ (0.1257 × 0.10958) = −0.04, and Φ(−0.04) puts him on the 48.4th percentile, just under the median of 7.93 kg. The 2nd and 98th lines at this age are 6.35 kg and 9.85 kg.
A girl measured between two monthly rows. Born 15 January 2026 and weighed on 4 October 2026, she is 262 days old: 262 ÷ 30.4375 = 8.608 months. Her L, M and S are taken 0.6078 of the way from the 8-month row to the 9-month row (M = 8.117 kg), so 8.2 kg is z = 0.08, the 53.3rd percentile.
The common mistake: rounding the age to whole months. For the same girl, using 8 months gives the 60.1st percentile and 9 months the 49.0th. In the first year babies gain weight quickly, so even two weeks shift the percentile by several points.
Show Work
Formulas
The WHO Growth Standards
The World Health Organization released its growth charts for children from birth to 5 years in April 2006. They come from the WHO Multicentre Growth Reference Study, run from 1997 to 2003 in Pelotas (Brazil), Accra (Ghana), Delhi (India), Oslo (Norway), Muscat (Oman) and Davis (California). Babies in the under-2 charts were followed from birth to 23 months, and the mothers did not smoke, breastfed and lived where money did not hold back growth; the average length of the babies at the six sites turned out to be almost identical.
Because they describe how healthy babies grow in good conditions, the WHO charts are a standard rather than a plain reference. In 2010 the CDC, after a panel with the National Institutes of Health and the American Academy of Pediatrics, recommended them for all US children under 24 months, with the 2.3rd and 97.7th percentiles as the cut-offs, and kept the CDC 2000 charts from age 2. Like the CDC charts, the WHO curves are smoothed with an LMS method, so any measurement turns into a z-score with one formula.
The table this calculator uses is the CDC’s own file of the WHO L, M and S values by month and by length.
About This Tool
This calculator reads the WHO weight-for-age, length-for-age, head circumference-for-age and weight-for-length tables for your baby’s sex, interpolates between monthly rows (or half-centimetre rows for length) for the exact age, and gives every percentile your measurements allow. Weight can be typed in kilograms, pounds, or pounds and ounces; length and head size in centimetres or inches. It covers birth to 24 months. From 2 years, CDC recommends its own charts: for BMI-for-age, use the Child BMI Percentile Calculator. If your baby was born early, ask your baby’s doctor whether to use corrected age; the Corrected Age Calculator works it out.
A percentile is a comparison, not a grade: babies on the 10th and the 90th percentile can be equally healthy. What doctors watch is how a baby follows the curves over several visits. For general information only — not medical advice. Talk to a doctor or other qualified professional about your own health or your baby’s.
Everything runs in your browser; nothing you enter is sent anywhere.
Related tools: Child BMI Percentile Calculator, Corrected Age Calculator, and Height Calculator.
Frequently Asked Questions
What does my baby’s percentile mean?
It is the share of babies of the same age and sex in the WHO reference who measure less. A 6-month-old boy weighing 7.9 kg is on the 48.4th percentile: a little under half of the WHO reference boys weighed less. The 50th-percentile weight for boys at 6 months is 7.93 kg.
Why WHO charts and not CDC charts?
Since 2010 the CDC has recommended the 2006 WHO growth standards for all children under 24 months, whatever the feeding, because they were built from healthy, mostly breastfed babies measured in six countries. From age 2 the CDC charts are used; for BMI from 2 to 19 years use the Child BMI Percentile Calculator.
Which percentiles should I pay attention to?
With the WHO charts, CDC recommends the 2.3rd and 97.7th percentiles, 2 standard deviations from the median, printed as the 2nd and 98th lines. For a boy at 6 months that is 6.35 kg to 9.85 kg. Between them is the usual range; outside them is a reason for a doctor to take a closer look, not a diagnosis.
Do days of age matter?
In the first months, yes. A girl of 8.2 kg is on the 53.3rd percentile at 8 months 18 days, but the 60.1st if her age is rounded down to 8 months and the 49.0th if rounded up to 9. With dates, age in months is the days between them ÷ 30.4375.
What is weight-for-length?
It compares weight with babies of the same length, whatever their age, so it shows whether weight is in proportion to length. A girl of 74 cm and 9 kg is on the 52.0th percentile; the WHO chart covers lengths from 45 to 110 cm.
How do I use the Baby Growth Percentile Calculator (WHO, 0–2 years)?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
After a check-up
A girl born 15 January 2026 and measured on 4 October 2026 (262 days, 8.61 months) at 8.2 kg is on the 53.3rd percentile for weight and the 40.2nd for her 69 cm length.
US units at home
A 10-day-old boy of 7 lb 8 oz and 20 in is on the 27.0th percentile for weight and the 36.2nd for length; a 14 in head is the 55.6th.
Head growth
A head circumference of 47.5 cm at 18 months is the 53.9th percentile for boys, against a median of 47.4 cm.
Weight in proportion
At 74 cm, a 9 kg girl is on the 52.0th percentile for weight-for-length, so her weight matches her length.
Boys and girls differ
At 12 months 9 kg is the 26.3rd percentile for a boy but the 51.9th for a girl, so the right chart matters.
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