The pediatrician says "30th percentile," writes it down, and moves on. You nod. Then, in the car, the question lands: is 30th good? Is my child small? Here is what that number actually means, what doctors look for instead, and the one comparison most parents never make.
Check your child's percentile on CDC growth charts →
Picture a line of 100 kids
Illustration. Each dot is one child of the same age and sex.
The charts most U.S. pediatricians use for ages 2 to 20 are the 2000 CDC growth charts, built from national health surveys of American children. For children under 2, the CDC recommends the World Health Organization charts instead. Boys and girls have separate charts because they grow on different schedules, especially around puberty.
What doctors look at instead of one number
A single measurement says little. Researchers in the Netherlands tested different "refer to a specialist" rules on real growth records to see which ones caught children with an underlying growth problem without flagging thousands of healthy kids. For children aged 3 to 10, the most useful signal was not the percentile itself. It was the distance between a child's height and the target range set by the parents' heights, combined with very short stature.
The comparison most parents never make
Because genes explain so much of height, a child of two shorter parents can sit on the 15th percentile and be right where you would expect. The same percentile in a child of two tall parents tells a different story. Pediatricians estimate the expected range like this:
| Step | Boys | Girls |
|---|---|---|
| 1. Add both parents' heights | Father's height + mother's height | |
| 2. Adjust for sex | Add 13 cm (5 in) | Subtract 13 cm (5 in) |
| 3. Divide by 2 | This is the mid-parental height | |
| 4. Expected range | About 8.5 cm (3.3 in) above or below it | |
Our growth percentile calculator does this math for you and shows where your child sits on the CDC curve.
When it is worth asking your pediatrician
Bring it up at the next visit, or sooner, if you notice any of these:
- Very short for age. Height well below the 3rd percentile line.
- Far from the family range. Height clearly below what both parents' heights predict.
- Dropping across lines. A child who used to track the 50th line and now sits near the 10th.
Most of the time the answer is reassuring. Children also grow in spurts, so two measurements a few months apart can look uneven.
Where nutrition fits
Genes set the range. Everyday basics help a body grow normally within it: enough food overall, protein, sleep, activity, and minerals such as calcium and iron. Teens need 1,300 mg of calcium a day, more than any other age group, and most of the bone a person will ever have is built by the late teens. We explain what that looks like on a plate in The Bone Bank Is 90% Full by 17.
See what's inside
Questions readers ask
- Is the 50th percentile "normal" and everything else not?
- No. The 50th is the middle of the line, not a target. Children across the chart are healthy.
- How should I measure at home?
- Shoes off, heels against a wall, a flat book on the head, and mark the wall. Measure at the same time of day each time, since people are slightly taller in the morning.
- Which chart should I use for a toddler?
- Under age 2, the CDC recommends the WHO growth charts. From 2 to 20, the CDC charts.
- Can a supplement change my child's percentile?
- Height is set mostly by genes. Nutrition supports normal growth; it is not a way to move a child up the chart.
Next in Height Questions, Answered Honestly: Can short parents have tall children? · Growth percentile calculator
- Kuczmarski RJ, et al. 2000 CDC Growth Charts for the United States: methods and development. Vital Health Stat 11. 2002;(246):1-190.
- Grummer-Strawn LM, et al. Use of World Health Organization and CDC growth charts for children aged 0-59 months in the United States. MMWR Recomm Rep. 2010;59(RR-9):1-15.
- Grote FK, et al. Developing evidence-based guidelines for referral for short stature. Arch Dis Child. 2008;93(3):212-217. doi:10.1136/adc.2007.120188
- Silventoinen K, et al. Heritability of adult body height: a comparative study of twin cohorts in eight countries. Twin Res. 2003;6(5):399-408. doi:10.1375/136905203770326402
- Tanner JM, Goldstein H, Whitehouse RH. Standards for children's height at ages 2-9 years allowing for heights of parents. Arch Dis Child. 1970;45(244):755-762. doi:10.1136/adc.45.244.755
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for general education and is not medical advice. Talk with your pediatrician about your child's growth.
