How to read your baby's growth curve
One measurement tells you where your baby is today. Several measurements show the curve, and the curve is what pediatricians look at. A baby who stays near the 10th percentile from visit to visit is growing as steadily as one who stays near the 90th.
Two patterns get a closer look. The first is a measurement beyond the 2.3rd or 97.7th percentile (2 standard deviations from the median), the cutoffs the CDC recommends for WHO charts. The second is a curve that crosses two major percentile lines over time, the usual trigger for a growth evaluation. Neither is a diagnosis: some healthy children are small or large, and some settle onto a new curve in the first months.
Newborns lose some weight in the first days and are usually back to birth weight by about 2 weeks, so an early dip in the weight curve is expected. For the meaning of each percentile, see how to read a growth chart and what it means when a baby drops on the chart. If your baby has always tracked near the bottom of the chart, read when a low percentile is fine; for how feeding and family background show up on the chart, see breastfed vs. formula-fed growth and growth charts for different ethnicities.
WHO lines vs. US clinic lines
Both versions use the same WHO data; they just draw different percentile lines. Counting “lines crossed” only makes sense on the chart your pediatrician uses, so the calculator lets you switch.
| Chart | Percentile lines | Used by |
|---|---|---|
| WHO's own charts | 3rd, 15th, 50th, 85th, 97th | Most countries, birth to 5 years |
| CDC-printed WHO charts | 2nd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, 98th | US clinics, birth to 24 months |
Sources: WHO; CDC WHO-based chart. The 2nd and 98th lines are the 2.3rd and 97.7th percentiles, rounded. On US charts, the calculator counts the 5th–95th lines as the major lines, as the AAFP does.
Frequently asked questions
How do I plot my baby on a growth chart?▾
Enter your baby's sex and date of birth, choose weight, length or head size, then add each measurement with its date (birth weight and the numbers from past checkups work well). The calculator works out the age at each visit, places every point on the WHO chart, and shows the percentile and z-score for each one.
What does it mean if my baby crosses percentile lines?▾
A steady curve at any percentile is reassuring. Falling across two major percentile lines over time is the usual trigger for a growth evaluation, so mention it to your pediatrician. Rising across two lines is also worth discussing. A single odd point is often a measuring error, so look at the overall trend.
Why is the percentile different from my pediatrician's?▾
Small differences are normal. Clinics may round ages differently, use a different scale, or measure length lying down with a measuring board, which is more accurate than a tape at home. From age 2, US pediatricians also switch from WHO to CDC charts, so their percentiles can differ slightly from the WHO percentiles shown here.
Which growth chart is right for my baby?▾
The CDC recommends WHO growth charts for all children under 2 in the US, whether breastfed or formula-fed, and CDC charts from age 2. Most other countries use WHO standards up to age 5. This calculator uses the WHO standards from birth to 5 years.
How often should I measure my baby?▾
Your pediatrician measures weight, length and head size at each well-child visit: in the first week, and at 1, 2, 4, 6, 9, 12, 15, 18 and 24 months. Those clinic numbers are the most accurate ones to plot.
Sources
- CDC MMWR (2010): Use of WHO and CDC growth charts for children aged 0–59 months in the United States
- CDC: WHO-based length-for-age and weight-for-age chart for girls, birth to 24 months (percentile lines)
- WHO Child Growth Standards
- AAFP (2016): Failure to Thrive, A Practical Guide (crossing two major percentile lines)
- AAP Bright Futures: Recommendations for Preventive Pediatric Health Care (periodicity schedule)
- AAP (HealthyChildren.org): Your newborn's first month, growth
- WHO Anthro software (z-score method, including the adjustment beyond ±3 SD)