What do baby growth percentiles mean?
A percentile shows how your baby compares with 100 healthy babies of the same age and sex. At the 30th percentile for weight, your baby weighs more than 30 of them and less than 70.
Percentiles are a snapshot. Pediatricians care much more about the pattern over several visits: a baby who tracks steadily along the 10th percentile is usually growing just as well as one who tracks along the 90th. The WHO considers anything between roughly the 3rd and 97th percentile to be within the normal range.
WHO vs CDC growth charts
The WHO Child Growth Standards describe how healthy children should grow under ideal conditions, based on breastfed babies from Brazil, Ghana, India, Norway, Oman and the USA. Since 2010, the CDC and AAP have recommended them for all children from birth to 2 years in the U.S. — including formula-fed babies. From age 2, U.S. pediatricians switch to the CDC growth charts.
One practical difference: on WHO charts, the CDC suggests using the 2.3rd and 97.7th percentiles (±2 standard deviations) as the cut-offs for “unusually low or high”, rather than the 5th and 95th used on CDC charts.
Average baby weight by month (WHO)
The 50th percentile is the median. Babies between the 3rd and 97th percentile are within the typical range.
| Age | Boys 3rd | Boys 50th | Boys 97th | Girls 3rd | Girls 50th | Girls 97th |
|---|---|---|---|---|---|---|
| Birth | 2.5 kg (5.5 lb) | 3.3 kg (7.4 lb) | 4.3 kg (9.6 lb) | 2.4 kg (5.4 lb) | 3.2 kg (7.1 lb) | 4.2 kg (9.2 lb) |
| 1 mo | 3.4 kg (7.6 lb) | 4.5 kg (9.9 lb) | 5.7 kg (12.6 lb) | 3.2 kg (7.1 lb) | 4.2 kg (9.2 lb) | 5.4 kg (11.9 lb) |
| 2 mo | 4.4 kg (9.7 lb) | 5.6 kg (12.3 lb) | 7.0 kg (15.4 lb) | 4.0 kg (8.8 lb) | 5.1 kg (11.3 lb) | 6.5 kg (14.4 lb) |
| 3 mo | 5.1 kg (11.2 lb) | 6.4 kg (14.1 lb) | 7.9 kg (17.5 lb) | 4.6 kg (10.2 lb) | 5.8 kg (12.9 lb) | 7.4 kg (16.3 lb) |
| 4 mo | 5.6 kg (12.4 lb) | 7.0 kg (15.4 lb) | 8.6 kg (19.0 lb) | 5.1 kg (11.2 lb) | 6.4 kg (14.2 lb) | 8.1 kg (17.9 lb) |
| 5 mo | 6.1 kg (13.4 lb) | 7.5 kg (16.6 lb) | 9.2 kg (20.3 lb) | 5.5 kg (12.1 lb) | 6.9 kg (15.2 lb) | 8.7 kg (19.2 lb) |
| 6 mo | 6.4 kg (14.2 lb) | 7.9 kg (17.5 lb) | 9.7 kg (21.4 lb) | 5.8 kg (12.8 lb) | 7.3 kg (16.1 lb) | 9.2 kg (20.3 lb) |
| 9 mo | 7.2 kg (16.0 lb) | 8.9 kg (19.6 lb) | 10.9 kg (24.0 lb) | 6.6 kg (14.5 lb) | 8.2 kg (18.1 lb) | 10.4 kg (22.9 lb) |
| 12 mo | 7.8 kg (17.3 lb) | 9.6 kg (21.3 lb) | 11.8 kg (26.1 lb) | 7.1 kg (15.7 lb) | 8.9 kg (19.7 lb) | 11.3 kg (25.0 lb) |
| 15 mo | 8.4 kg (18.5 lb) | 10.3 kg (22.7 lb) | 12.7 kg (27.9 lb) | 7.7 kg (16.9 lb) | 9.6 kg (21.2 lb) | 12.2 kg (26.9 lb) |
| 18 mo | 8.9 kg (19.6 lb) | 10.9 kg (24.1 lb) | 13.5 kg (29.7 lb) | 8.2 kg (18.0 lb) | 10.2 kg (22.6 lb) | 13.0 kg (28.6 lb) |
| 21 mo | 9.3 kg (20.6 lb) | 11.5 kg (25.5 lb) | 14.3 kg (31.5 lb) | 8.7 kg (19.1 lb) | 10.9 kg (23.9 lb) | 13.8 kg (30.4 lb) |
| 24 mo | 9.8 kg (21.6 lb) | 12.2 kg (26.8 lb) | 15.1 kg (33.2 lb) | 9.2 kg (20.2 lb) | 11.5 kg (25.3 lb) | 14.6 kg (32.2 lb) |
Most babies lose up to 7–10% of their birth weight in the first few days and regain it by about 2 weeks. On average they double their birth weight by around 4–5 months and triple it by their first birthday.
When to talk to your pediatrician
- Weight, length or head circumference is below the 2nd or above the 98th percentile.
- Your baby crosses two or more major percentile lines (for example, from the 75th to below the 25th) between visits.
- Weight-for-length is very low or very high.
- Head circumference is growing much faster or slower than length and weight.
- Your baby isn’t feeding well, has fewer wet diapers, or seems unusually sleepy.
Born early? Use your baby’s corrected age — enter the original due date as the birth date. Our baby age calculator shows corrected age too.
How to measure your baby at home
- Weight: weigh yourself, then weigh yourself holding your baby (without clothes or diaper) and subtract. A baby scale is more accurate.
- Length: lay your baby flat, straighten one leg gently and measure from the top of the head to the bottom of the heel. Babies are measured lying down until age 2.
- Head circumference: wrap a soft tape just above the eyebrows and ears, around the widest part of the back of the head.
Growth goes hand in hand with feeding and sleep — see how much sleep your baby needs in our baby sleep schedule by age.
Frequently asked questions
What does it mean if my baby is in the 50th percentile?
It means your baby measures right in the middle: half of healthy babies of the same age and sex are smaller and half are larger. The 50th percentile is not a target — any percentile between the 3rd and 97th can be completely normal.
Is a low percentile bad?
Not by itself. Small parents often have small, healthy babies. What matters most is steady growth along a similar curve over time. Doctors look more closely if a baby is below about the 2nd percentile, above the 98th, or drops or rises across two major percentile lines.
Which growth chart does this calculator use?
It uses the WHO Child Growth Standards, which the CDC and the American Academy of Pediatrics recommend for all children under 2 in the United States. They are based on healthy breastfed babies from six countries.
Should I use corrected age for a premature baby?
Yes. For babies born before 37 weeks, plot growth using corrected age (age from the due date) until about 2 years old. Enter the due date as the birth date in this calculator to get corrected-age percentiles.
Why is my baby’s weight percentile different from their length percentile?
That’s very common. Babies have different builds, just like adults. A baby at the 25th percentile for weight and the 75th for length is longer and leaner than average, which is usually fine if both are steady over time.
How accurate are home measurements?
Measuring a wriggly baby at home is tricky — length can easily be off by a centimeter or more, which can shift the percentile a lot. Use the measurements from your pediatrician’s office when you can.
Sources
- World Health Organization — Child Growth Standards (length/height-for-age, weight-for-age, head circumference-for-age)
- CDC — Use of WHO growth charts for children under 2 in the United States (MMWR 2010;59(RR-9))
- CDC — WHO Growth Charts
- AAP / HealthyChildren.org — Understanding growth charts: percentiles and z-scores