Child Growth Percentile Calculator
Work out your child’s height, weight, BMI and head circumference percentiles against the WHO Child Growth Standards (0–60 completed months, birth to 5 years). Enter as many or as few measurements as you have.
Growth Chart
Percentile Breakdown
- This tool covers 0–60 completed months (birth to 5 years) only.
- BMI-for-age uses a length-based reference under 2 years and a height-based reference from 2 years, matching WHO convention.
- A single reading is a snapshot — your child’s own Red Book chart, tracked over multiple visits, is the more reliable picture.
- Percentiles outside the 2nd–98th range aren’t unusual on their own, but are worth mentioning at your next health visitor or GP appointment.
Child Growth Percentile Calculator (WHO Standards, 0–5 Years)
Our Child Growth Percentile Calculator works out where your child’s height, weight, BMI and head circumference sit against the WHO Child Growth Standards for 0–60 completed months. These standards form the basis of the UK-WHO growth charts used in the UK’s Personal Child Health Record (“Red Book”), although the UK charts also incorporate UK-specific birth and preterm data. Enter a date of birth, a measurement date and whichever measurements you have to see a percentile and z-score for each.
What Is a Growth Percentile?
A percentile shows how a measurement compares with other children of the same age and sex in the reference population. A child on the 25th percentile for weight is heavier than roughly 25% of children their age and sex, and lighter than the other 75%. Being on a high or low percentile isn’t in itself a problem — children come in a wide range of healthy shapes and sizes. What health visitors and GPs generally pay closer attention to is how a child tracks over time along their own curve, and whether there’s a sudden jump or drop across several measurements.
How to Use This Calculator
- Enter your child’s date of birth and the date of the measurement. These are used together to work out age in months.
- Select sex — growth references differ between boys and girls.
- Enter any measurements you have — height/length, weight and/or head circumference. You don’t need all three.
- If both height and weight are entered, BMI is calculated automatically and checked against the BMI-for-age reference.
- Click Calculate Percentiles to see a percentile, z-score and plain-language range for each measurement, plus a growth chart.
Which Growth Standard Does This Use?
This calculator uses the WHO Child Growth Standards (World Health Organization, 2006 for weight/length/BMI/head circumference under 5 years), which are freely published international reference data covering 0–60 completed months. Unlike some older growth references built from a general population sample, the WHO standards describe how children grow under optimal conditions — adequate nutrition, breastfeeding and a healthy environment — which is why they’re used as the growth standard for children under 5 across the NHS and internationally.
This tool currently covers 0–60 completed months (birth to 5 years) only. For older children, your GP practice or school nursing team can plot growth using the 2–18 years UK-WHO charts in your child’s Red Book.
Understanding the Percentile Bands
| Percentile range | What it generally means |
|---|---|
| Below 2nd | Notably smaller than most children of the same age and sex — worth mentioning at your next check-up |
| 2nd – 25th | Smaller side of the typical range |
| 25th – 75th | Around the middle of the typical range |
| 75th – 98th | Larger side of the typical range |
| Above 98th | Notably larger than most children of the same age and sex — worth mentioning at your next check-up |
These bands describe where a measurement sits in the reference population — they are not a diagnosis. A single measurement outside these ranges is common and often unremarkable; a consistent pattern over several measurements, or a sudden crossing of percentile lines, is what health visitors and GPs tend to look at more closely.
Why Track More Than One Measurement?
- A single reading is a snapshot. Growth charts are most useful when several measurements are plotted over time, showing the direction and pace of growth rather than one point.
- Percentile crossing matters more than the percentile itself. A child who moves from the 50th to the 9th percentile over a few months is generally of more interest to a clinician than a child who has always tracked around the 9th percentile.
- BMI-for-age in young children behaves differently to adult BMI. There’s no “overweight” or “underweight” cut-off built into this tool — BMI-for-age in the under-5s is interpreted alongside the whole growth picture, not as a standalone number.
Frequently Asked Questions
Is a low or high percentile a cause for concern?
Not on its own. Percentiles describe where a child sits compared with a reference population, not whether they’re healthy. Many perfectly healthy children sit consistently on a low or high percentile throughout childhood. What tends to prompt a closer look is a sudden change in percentile over time, or a measurement a long way outside the typical range combined with other signs. Your health visitor or GP is best placed to interpret a measurement in the context of your child’s overall growth and history.
Why does this calculator only cover ages 0–5?
The WHO Child Growth Standards used here are published for birth to 5 years. Growth references for older children and teenagers (5–18 years) use a different WHO reference and require additional puberty-related considerations, which sit outside the scope of this tool. Your child’s Red Book or GP practice will have access to the 2–18 years charts.
Should I use length or height?
Children under 2 are usually measured lying down (length); children 2 and over are usually measured standing (height). This calculator automatically switches to the appropriate WHO reference at 24 months based on the age you enter, so you can simply enter whichever measurement was taken.
How is BMI-for-age different from adult BMI?
Adult BMI uses fixed cut-offs (for example, 25 for “overweight”). Children’s bodies change shape naturally as they grow, so BMI-for-age instead compares a child’s BMI with other children of the same age and sex, in percentile form — the same approach used for height and weight. This calculator reports BMI-for-age as a percentile rather than applying an adult-style cut-off.
What if my child was born prematurely?
This calculator uses chronological age (age since birth), not corrected age. For babies born significantly premature, health visitors and GPs typically use “corrected age” (chronological age minus the number of weeks born early) when plotting growth, usually up to age 2. If your child was born prematurely, it’s worth asking your health visitor how they’re tracking growth for your child specifically.
Where do the reference figures come from?
The percentile calculations use the L, M and S parameters published by the World Health Organization as part of the WHO Child Growth Standards (2006 Multicentre Growth Reference Study, plus the 2007 head circumference standard), applied using the standard LMS statistical method. This calculator uses the WHO Child Growth Standards for 0–60 months. These standards form the basis of the UK-WHO growth charts, although UK charts also incorporate UK-specific birth and preterm data.