A growth percentile is a comparison, not a grade. This guide explains how the charts work, what pediatricians actually watch for, and how far a parent-based height prediction can be trusted.
At every well-child visit a child’s weight, length or height, and (in babies) head size are plotted on a growth chart. The number that comes back, such as "40th percentile," means 40% of children of the same age and sex in the reference group are smaller. It says nothing on its own about whether a child is healthy. What matters is the pattern over time.
Since 2010 the CDC has recommended that U.S. clinicians use the 2006 World Health Organization growth standards for children under 24 months and the 2000 CDC growth charts from age 2 to 19. The WHO charts are a standard: they describe how healthy, breastfed infants grow in good conditions. The CDC charts are a reference: they describe how U.S. children happened to grow in national surveys. Because the reference groups differ, a child’s percentile can shift at the 2-year visit without any change in growth. The baby growth percentile calculator uses the WHO standards and the child growth percentile calculator uses the CDC charts.
Both chart sets publish three values for each age and sex: L (a skew correction), M (the median) and S (the spread). A measurement X becomes a z-score with z = ((X ÷ M)L − 1) ÷ (L × S), and the percentile is the share of a normal distribution below that z-score. A z-score of 0 is the 50th percentile; −2 and +2 are about the 2.3rd and 97.7th.
Children tend to follow their own percentile curve once early growth settles. Heights on the CDC chart for girls at five percentiles:
| Age | 3rd | 25th | 50th | 75th | 97th |
|---|---|---|---|---|---|
| 2 | 31.0 in | 32.7 in | 33.6 in | 34.5 in | 36.2 in |
| 5 | 39.0 in | 41.1 in | 42.4 in | 43.7 in | 46.1 in |
| 8 | 46.1 in | 48.7 in | 50.2 in | 51.8 in | 54.8 in |
| 11 | 51.4 in | 54.8 in | 56.7 in | 58.6 in | 62.1 in |
| 14 | 58.3 in | 61.4 in | 63.1 in | 64.9 in | 68.0 in |
| 18 | 59.4 in | 62.5 in | 64.2 in | 65.9 in | 69.0 in |
A girl who stays near the 25th percentile is growing as steadily as one on the 75th; she is simply on a lower curve. An 8-year-old girl at the median is about 50.2 inches tall.
Pediatricians act on trends in repeated, accurate measurements, not on one number. The thresholds below come from CDC guidance and American Academy of Family Physicians reviews:
| Pattern | Threshold |
|---|---|
| Screening limits on the WHO charts (under 2) | Below the 2.3rd or above the 97.7th percentile |
| Faltering growth (failure to thrive) | Weight below the 5th percentile for corrected age, or weight falling across two major percentile lines (95, 90, 75, 50, 25, 10, 5) |
| Short stature | Height below the 3rd percentile (more than 2 SD below the mean) |
| Tall stature | Height above the 97th percentile |
| Weight status, ages 2 to 19 | BMI-for-age: under 5th underweight, 85th to under 95th overweight, 95th or above obesity |
Most children outside these lines are healthy. The AAFP review of short and tall stature notes that common causes are normal variants such as familial short stature and late puberty, and that children more than three standard deviations from the mean are more likely to have an underlying condition. For weight status, use the child BMI calculator, because weight-for-age ignores height.
The routine first check is mid-parental (target) height, from growth standards Tanner and colleagues published in 1970: average the parents’ heights, then add 6.5 cm for a boy or subtract 6.5 cm for a girl. The Royal Children’s Hospital Melbourne guideline gives a normal range of 8.5 cm either side. Three families, computed with the same formula as the height predictor calculator:
| Father / mother | Son: target (range) | Daughter: target (range) |
|---|---|---|
| 67 in / 62 in | 67.1 in (63.7–70.4) | 61.9 in (58.6–65.3) |
| 70 in / 64 in | 69.6 in (66.2–72.9) | 64.4 in (61.1–67.8) |
| 73 in / 67 in | 72.6 in (69.2–75.9) | 67.4 in (64.1–70.8) |
How good is it? In a study of 419 children aged 8 to 9, 90% were within about two percentile spaces of their mid-parental height, but children of unusually tall or short parents ended up closer to average than the formula predicts (Wright and Cheetham, 1999). Specialists who need a tighter estimate add the child’s own height and a bone-age X-ray.
Weigh babies without clothes or a diaper and measure length lying flat with the legs straight. Measure older children standing, shoes off, heels to the wall, with a flat object resting on the head. Use corrected age for babies born early, until about age 2: the corrected age calculator subtracts the weeks born early (40 minus gestational age) from actual age, as the AAP describes. And compare like with like: home numbers against home numbers, clinic against clinic. The same measurements decide car seat moves: children change stages when they reach the seat’s labeled weight or height limit, not on a birthday, and stay in a booster until the adult belt fits, typically at 4 ft 9 in and 8 to 12 years; the car seat stage calculator checks a child against those limits.
For a formula-fed baby, steady growth along a curve is the best sign that feeding is about right. The AAP’s rule of thumb is about 2½ ounces of formula a day per pound of body weight, usually no more than about 32 ounces in 24 hours, so a 10-pound baby takes about 25 ounces a day; the baby formula calculator applies it with AAP and CDC amounts per feeding by age. Babies regulate their own intake from day to day, so a weight curve that holds its line says more than any one day’s ounces.
Bring it up if your child’s height or weight crosses two major percentile lines, if height falls below the 3rd percentile or far below the family’s expected range, if growth seems to stall for months, if a baby is feeding poorly or has fewer wet diapers, or if puberty begins much earlier or later than in peers. Calculators on this site give estimates, not diagnoses; the pediatrician interprets the full trend with an exam.
CDC. Use of WHO and CDC growth charts for children aged 0-59 months in the United States. MMWR Recomm Rep 2010;59(RR-9):1-15 (PubMed 20829749; cdc.gov). Homan GJ. Failure to Thrive: A Practical Guide. Am Fam Physician 2016;94(4):295-9 (PubMed 27548594). Barstow C, Rerucha C. Evaluation of Short and Tall Stature in Children. Am Fam Physician 2015;92(1):43-50 (PubMed 26132126). CDC. BMI categories for children and teens (updated June 28, 2024). Tanner JM, Goldstein H, Whitehouse RH. Arch Dis Child 1970;45(244):755-62 (doi:10.1136/adc.45.244.755). Wright CM, Cheetham TD. Arch Dis Child 1999;81(3):257-60 (doi:10.1136/adc.81.3.257). The Royal Children’s Hospital Melbourne, Short stature pre-referral guideline (reviewed July 2025). CDC 2000 stature-for-age LMS data file (accessed October 2026). AAP HealthyChildren.org, Your Preemie’s Growth & Developmental Milestones (updated Sept 24, 2024) and Amount and Schedule of Baby Formula Feedings (updated May 16, 2022).
There is no target percentile. A child growing steadily along any curve between the usual limits is typical; changes in the curve matter more than its level.
U.S. clinics switch from the WHO standards to the CDC charts at 2, and the two charts use different reference groups.
Not necessarily. Infant size reflects more than genes, and pediatricians judge adult height potential from the parents’ heights and the child’s growth over the years.
Most children land within about 8.5 cm of the mid-parental target, but the method is less reliable when parents are very tall or very short.
No. From age 2, BMI-for-age percentile is used, because it accounts for height.
You can, but home measurements are less precise; share concerns with the pediatrician rather than reacting to a single home reading.