Baby Percentile Calculator

Enter your baby's measurements to see where they sit among babies the same age on the WHO growth charts.

Baby's sex
Units

How to read a growth chart

Each line on a growth chart is a percentile. If your baby's measurement sits on the 25th percentile line, they are bigger than 25 percent of babies their age and smaller than 75 percent. Healthy babies usually grow along a fairly steady line, which is why checkups look at how measurements move over time rather than a single value.

Measuring accurately

  • Weight: weigh your baby undressed or in a clean diaper, on the same scale, at a similar time of day.
  • Length: under age 2, length is measured lying down with legs straight and head steady.
  • Head circumference: use a non-stretch tape just above the eyebrows and around the widest part of the back of the head.

Home measurements can be slightly off. Repeat a surprising result and go by your pediatrician's measurement. For month by month milestones, see baby development by month.

Frequently asked questions

What does a percentile mean?

A percentile shows where your baby sits among 100 babies of the same age and sex. A weight at the 40th percentile means 40 babies weigh less and 60 weigh more. The 50th percentile is the average, but it is not the "best" value.

What percentile is normal for a baby?

On WHO charts, the 3rd to 97th percentile is generally considered within the normal range. What matters most is that your baby follows their own curve over time. Changes that cross two major percentile lines up or down should be reviewed by your pediatrician.

How do you calculate percentiles for a premature baby?

For babies born before 37 weeks, corrected age is used: the time they were born early, counted to 40 weeks, is subtracted from their age. This correction is usually used until age 2. Choose the birth week in the calculator and the correction is applied automatically.

Should I worry if my baby is in a low percentile?

A baby with smaller parents can grow steadily along a low percentile and be perfectly healthy. Contact your pediatrician if the percentile drops quickly, weight gain stops, feeding is difficult or there are fewer wet diapers.

Which growth charts does this calculator use?

It uses the World Health Organization Child Growth Standards (2006), which the CDC recommends for children under 2 in the US. Calculations use the published WHO LMS parameters and cover 0 to 36 months.