My Baby
Free tool
Baby growth percentile calculator
Weight, length and head circumference on the WHO charts, for girls and boys from birth to 5 years. The maths runs on your device: nothing you type is sent anywhere.
This calculator is for information only and does not replace an assessment by your doctor or health visitor. One point on its own says little: what matters is the curve over the months.
What a percentile is
A percentile compares a measurement with those of other children of the same sex and age. A weight on the 30th percentile means that out of 100 children, 30 weigh less and 70 weigh more. It is not a score: the 50th percentile is no better than the 15th or the 85th.
Which charts the calculator uses
The World Health Organization (WHO) Child Growth Standards, published in 2006 and used in the child health records of many countries. They were built from breastfed, well-cared-for children in Brazil, Ghana, India, Norway, Oman and the United States. Girls and boys have separate charts. Up to 2 years, length is measured lying down; after that, height is measured standing up.
Premature babies
For babies born before 37 weeks, corrected age is usually used up to 2 years: the time that was missing to reach 40 weeks is taken off the age. Choose the weeks of pregnancy under "Born premature?" and the calculator does the maths.
When to talk to your doctor
Take any questions to the check-up, especially if a measurement suddenly moves across the lines from one visit to the next, or sits below the 3rd or above the 97th percentile. Only the doctor who examines the child can say what a number means for them.
Frequently asked questions
What is a normal percentile for a baby?
There is no right percentile. Most healthy children sit between the 3rd and the 97th, and what matters is that the child follows their own curve over time.
What is the difference between a percentile and a z-score?
They are two ways of saying the same position on the chart. The z-score counts how many standard deviations the measurement is above or below the median: z 0 is the 50th percentile, z +2 is close to the 98th and z −2 close to the 2nd.
Does the calculator keep what I type?
No. The calculation runs in your browser, and nothing is sent or stored. To follow measurements over time, My Baby keeps the weight and height from each check-up on a growth chart.
Up to what age does the calculator work?
From birth to 5 years, the span of the WHO growth standards for weight, length and head circumference.
Source: WHO Child Growth Standards (2006).