About the Child Growth Percentile Calculator
Our adult BMI calculator tells parents to look elsewhere for children, because a child’s numbers only mean something against other children of the same age and sex. This is the elsewhere: weight-for-age, length or height-for-age, head circumference-for-age and BMI-for-age, each as a percentile and a z-score, plotted on the real curves.
The references are the ones a US paediatric office uses. From birth to 24 months, the WHO Child Growth Standards, scored to the exact day of age with the WHO’s own method, including its restricted calculation beyond three standard deviations. From 2 to 20 years, the 2000 CDC growth charts, scored the way the CDC’s own program does it, with the 2022 extended BMI percentiles above the 95th. The length-versus-height correction at the 24-month switch is applied automatically, and babies born early can be scored at their corrected age, which the American Academy of Pediatrics advises until age three.
Two things said plainly. Percentiles describe; they do not diagnose — the 5th percentile is as normal as the 50th. What matters is the line over time, and a change across two major percentile lines is the thing to raise with a paediatrician. And your child’s numbers stay in your browser: the page downloads the reference tables once and does every calculation locally.
Save each check-up here and the chart draws the child’s own line through the curves. Stored only in this browser; nothing is uploaded. A change across two or more major percentile lines between visits is flagged, because that is the pattern worth a conversation with your paediatrician.
Tanner’s 1970 formula: the parents’ average height, plus 6.5 cm for a boy or minus 6.5 cm for a girl, with a target range of ±8.5 cm. It sets a family expectation, not a prediction.
One page: weight and length or height on the curves, the percentile table and every saved visit — the thing to hand the paediatrician instead of reading numbers off a phone.
How to Use the Child Growth Percentile Calculator
Choose boy or girl, enter the date of birth and the date the measurements were taken, then the weight, the length or height and, if you have it, the head circumference. Say whether the length was measured lying down or standing and press Plot Percentiles. Every measurement gets a percentile, a z-score and the name of the reference that produced it, and the chart shows the point on the actual percentile curves. Use the numbers from the clinic’s own scale and board where you can: a home bathroom scale with a squirming toddler is easily half a kilogram out, which at 12 months is a difference of about ten percentile points.
What a Percentile Actually Says
A percentile ranks one measurement against healthy children of the same sex and exact age. The 25th percentile means a quarter of the reference children were smaller. It is a position, not a score: a child on the 5th percentile curve is not doing a fifth as well as one on the 100th. The z-score is the same position in standard deviations from the median, which is how clinicians compare across ages and how extreme values are expressed: a z-score of −2 is roughly the 2nd percentile, and anything beyond ±3 is rare enough that a measuring mistake is the first thing to rule out. The calculator flags values outside the range the WHO and CDC treat as biologically plausible, which is almost always a typo, a unit mix-up or a misplaced decimal.
WHO Before Two, CDC After
Since 2010 the CDC has recommended the WHO Child Growth Standards for children under 24 months. They were built from children in six countries raised in conditions that favour healthy growth, most of them breastfed, so they describe how babies should grow rather than how a particular population happened to grow. From 2 to 20 years the CDC 2000 charts remain the US reference. The practical consequences:
- Breastfed babies look different on the two. On the older CDC infant charts, breastfed babies often appeared to “fall off” their weight curve around 6–12 months; on the WHO standards that dip largely disappears, because breastfed growth is the standard.
- The switch at 24 months can move a child a few points. The two references were built differently and do not join perfectly.
- Length becomes height. The WHO adds 0.7 cm to a standing height under two; the CDC subtracts 0.8 cm from a lying length after two. This calculator applies whichever correction the chart in use calls for.
Reading BMI for a Child
Children’s BMI follows its own curve: it rises in the first year, falls to a low point somewhere around age 5 or 6 — the adiposity rebound — and climbs again through adolescence. That is why a single adult cut-off cannot work. From age 2 the CDC classes BMI-for-age as underweight below the 5th percentile, healthy from the 5th to below the 85th, overweight from the 85th to below the 95th and obesity at the 95th and above, with severe obesity at 120% of the 95th percentile value. Above the 95th percentile the 2000 charts ran out of data, so in 2022 the CDC added extended BMI percentiles that keep distinguishing a child just over the line from one far beyond it. This calculator uses them, which is why a very high BMI here can read, for example, 98.7th rather than the 99.9th an older calculator would show.
The Pattern That Matters
Most children track a percentile channel loosely, drifting a little between visits. Paediatricians pay attention when a measurement crosses two or more major percentile lines (the 5th, 10th, 25th, 50th, 75th, 90th and 95th) over time, when a value sits below the 3rd or above the 97th, or when weight and length move in different directions. None of these is a diagnosis. Healthy babies often shift channels in the first year as they move toward their genetic size, and preterm babies need their corrected age — the AAP says until age 3 — or they will look small simply for being early. For short stature, the parents’ heights matter too, which is what the mid-parental target captures.
Related tools: the BMI Calculator for adults, the Due Date Calculator for the months before any of this, and the Sleep Calculator for the nights in between. Browse every Health & Fitness tool for more.
Educational information, not medical advice. Percentiles describe a child’s size relative to a reference; they do not diagnose. Bring concerns, and the measurements, to your child’s paediatrician. Preterm babies under their due date should be followed on preterm charts, which this tool does not provide.
Frequently Asked Questions
What does it mean if my baby is in the 10th percentile?
It means that out of 100 healthy children of the same age and sex in the reference population, about 10 would measure less and 90 more. It is not a grade and not a problem in itself: the 10th percentile is as normal as the 90th. What paediatricians watch is the pattern over several visits, and a child who steadily follows the 10th percentile curve is growing exactly as expected for that child.
Why are WHO charts used under 2 and CDC charts after?
Because that is what the CDC itself recommends for children in the United States. The WHO standards, published in 2006, describe how healthy breastfed infants grow under good conditions, which makes them a better yardstick for babies. The CDC charts from 2000 remain the US reference from age 2 to 20, the range where the WHO standards were never adopted for American children. The switch happens at 24 months, which is also where measurement changes from lying down to standing.
Why did my child drop in height percentile at the 2-year check-up?
Often it is the measurement, not the child. Babies are measured lying down and older children standing, and standing height is on average 0.7 to 0.8 cm shorter because the spine compresses and the posture changes. The chart also switches from WHO to CDC at 24 months, and the two references differ slightly. This calculator applies the published correction when the method does not match the chart, but a small apparent drop right at 2 years is common and usually meaningless.
When should I worry about a growth percentile?
A single percentile rarely means anything on its own. The patterns doctors look for are a change across two or more major percentile lines over time, a measurement below the 3rd or above the 97th percentile, or weight and height moving in very different directions. If you see any of those, bring the numbers to your paediatrician, who can check the measurements and the rest of the picture. This calculator describes growth; it cannot diagnose anything.
How is BMI for age different from adult BMI?
The formula is the same, weight in kilograms divided by height in metres squared, but the number is not read against fixed cut-offs. Children naturally get leaner from about age 1 to 6 and then heavier again, so a BMI of 17 can be high for a 5-year-old and low for a 15-year-old. From age 2 the CDC grades BMI by percentile: below the 5th is underweight, the 85th to 95th overweight, and the 95th and above obesity, now measured on the CDC 2022 extended percentiles.
