How do you calculate a baby's growth percentile?

A percentile is found by comparing your baby's measurement to the WHO Child Growth Standards for the same age and sex. The standard gives an expected distribution (using values called L, M, and S), and your baby's measurement is converted to a percentile on that curve. This tool does that math using the official WHO data for birth to 24 months.

What does it mean if my baby is in the 25th percentile?

It means that out of 100 babies of the same age and sex, about 25 would weigh (or measure) less and 75 would measure more. The 25th percentile is a normal, healthy place to be. A percentile is a comparison, not a grade. Most healthy babies sit somewhere between the 3rd and 97th percentiles.

Is a low or high percentile bad?

Not on its own. A baby can be healthy at the 5th or the 95th percentile. What pediatricians watch is the trend: a baby who steadily follows their own curve is usually fine, while a large, sudden jump or drop across percentile lines, or poor weight gain, is worth discussing. Always look at growth over time, not one number.

Baby Growth Percentile Calculator

What percentile is my baby in?

Enter your baby's weight, length, or head size to see their percentile against the official WHO Child Growth Standards, birth to 24 months. A percentile is a comparison, not a grade, and the trend over time matters more than any single number.

Free tool WHO standards Birth to 24 months

Baby

Measure

Age (months)

Measurement

What a percentile actually means

The 50th percentile is the middle: half of babies the same age and sex are bigger, half are smaller. It is not a target.
Most healthy babies fall between the 3rd and 97th percentiles. A baby can be perfectly healthy at the 10th or the 90th.
What pediatricians watch is the trend: a baby who follows their own curve is usually doing well.
A large, sudden jump or drop across percentile lines, or poor weight gain, is the signal worth a conversation, not the number itself.

WHO vs CDC charts

For children under 2 years, the WHO Child Growth Standards are recommended, including by the CDC and the AAP, because they describe how healthy, breastfed babies grow worldwide. This calculator uses the WHO standards. From age 2 onward, CDC growth charts are usually used. This tool covers birth to 24 months.

Talk to your pediatrician if

Your baby's growth crosses two or more major percentile lines up or down
Weight gain slows, stops, or drops off the curve
Your baby is below the 3rd or above the 97th percentile and the trend is changing
You are worried about feeding, growth, or your baby's energy and development

Your pediatrician plots growth at every well visit using the same standards, on the full curve. This tool is a quick check between visits, not a diagnosis. One number on one day rarely tells the whole story.

Quick answers

How do you calculate a baby's growth percentile?: A percentile is found by comparing your baby's measurement to the WHO Child Growth Standards for the same age and sex. The standard gives an expected distribution (using values called L, M, and S), and your baby's measurement is converted to a percentile on that curve. This tool does that math using the official WHO data for birth to 24 months.
What does it mean if my baby is in the 25th percentile?: It means that out of 100 babies of the same age and sex, about 25 would weigh (or measure) less and 75 would measure more. The 25th percentile is a normal, healthy place to be. A percentile is a comparison, not a grade. Most healthy babies sit somewhere between the 3rd and 97th percentiles.
Is a low or high percentile bad?: Not on its own. A baby can be healthy at the 5th or the 95th percentile. What pediatricians watch is the trend: a baby who steadily follows their own curve is usually fine, while a large, sudden jump or drop across percentile lines, or poor weight gain, is worth discussing. Always look at growth over time, not one number.
Should I use WHO or CDC growth charts?: For babies under 2 years old, the WHO Child Growth Standards are recommended, including by the CDC and AAP, because they describe how healthy, breastfed babies grow. This tool uses the WHO standards. From age 2 onward, CDC growth charts are typically used.

Sources & further reading

Calculations use the official WHO Child Growth Standards L, M, S parameters (weight-for-age, length-for-age, head-circumference-for-age), birth to 24 months, as published by the CDC.

Plot growth over time, not just one day.

ParentFlow records weight, length, and head size and shows the trend on WHO curves, so you see the pattern your pediatrician looks for.

App Store Google Play Open Web App

This tool uses the official WHO Child Growth Standards and is for educational purposes only. It gives an approximate percentile and is not a diagnosis. ParentFlow is a wellness companion — not a substitute for your pediatrician, who tracks your baby's full growth curve. For any concern about growth or feeding, contact your healthcare provider.