Quick answer: for a boy, add both parents’ heights, add 5 in (13 cm) and divide by 2; for a girl, subtract 5 in and divide by 2. About 95% of children end up within 3.3 in (8.5 cm) of this. The calculator also uses the child’s current growth percentile for a sharper estimate.
How the Height Calculator Works
This calculator combines two well-established methods:
- Mid-parental height (Tanner method): the parents’ average height, plus 6.5 cm (2.5 in) for a boy or minus 6.5 cm for a girl. About 95% of children end up within 8.5 cm of this target.
- Growth-curve projection: the child’s current percentile for age (from U.S. NHANES growth data) carried forward to adult height. A child on the 60th percentile at age 8 is projected to reach the 60th percentile as an adult.
When you enter both, the prediction blends them, leaning more on the growth curve as the child gets older, because an older child’s height already reflects more of their own growth pattern.
Mid-Parental Height Formula
| Child | Formula (cm) | Formula (inches) |
|---|---|---|
| Boy | (mother + father + 13) ÷ 2 | (mother + father + 5) ÷ 2 |
| Girl | (mother + father − 13) ÷ 2 | (mother + father − 5) ÷ 2 |
| Mother | Father | Boy | Girl |
|---|---|---|---|
| 5 ft 2 in | 5 ft 8 in | 5 ft 7.5 in | 5 ft 2.5 in |
| 5 ft 4 in | 5 ft 10 in | 5 ft 9.5 in | 5 ft 4.5 in |
| 5 ft 6 in | 6 ft 0 in | 5 ft 11.5 in | 5 ft 6.5 in |
| 5 ft 8 in | 6 ft 2 in | 6 ft 1.5 in | 5 ft 8.5 in |
How Children Grow
Children grow fastest in the first year (about 25 cm), then about 6 cm a year through early childhood. Growth speeds up again in puberty: girls typically gain 20 to 25 cm from about age 10 to 15, and boys 25 to 30 cm from about 12 to 17. See the full height-for-age chart in the height percentile calculator.
What Affects Final Height
Genetics explains roughly 80% of the variation in height between people. The rest comes from nutrition (especially protein and overall calories in childhood), sleep, chronic illness and the timing of puberty. Improving these can help a child reach their genetic potential, but no diet or supplement adds height beyond it. Population-wide, better childhood nutrition explains why many countries grew 10 to 20 cm taller over the past century (see average height by country).
How to Use the Calculator
- Measure the child. Stand the child barefoot against a wall, heels together, and mark the top of the head with a flat object. Note the exact age.
- Enter the parents’ heights. Use measured heights if possible; people often overestimate their own height by an inch or so.
- Read the prediction. The calculator shows the mid-parental estimate, the growth-curve estimate and a blended prediction with a likely range.
- Track over time. Repeat every 6 to 12 months. A steady curve is more informative than a single measurement.
To compare the predicted height with friends or family, use the height comparison tool.
Child Height Prediction FAQ
How accurate are height predictions?
The mid-parental method predicts adult height within about 8.5 cm (3.3 in) for roughly 95% of children. Combining it with the child’s current growth percentile, as this calculator does, narrows the range, especially for older children. Methods that use a hand X-ray of bone age, done by a doctor, are the most accurate.
How do you calculate a child’s adult height from the parents?
Add the mother’s and father’s heights. For a boy, add 13 cm (5 in) and divide by 2; for a girl, subtract 13 cm (5 in) and divide by 2. For example, parents of 5 ft 4 in and 5 ft 10 in give a boy about 5 ft 9.5 in and a girl about 5 ft 4.5 in.
Is it true that a child’s height at 2 doubles?
Roughly. A popular rule says boys reach about half their adult height by age 2 and girls by about 18 months, so doubling gives a rough estimate. It can easily be off by several inches.
When do children stop growing?
Girls usually stop growing about 2 years after their first period, around age 15 to 16. Boys usually stop around 17 to 19. A few late developers keep growing slightly into their early 20s.
Can a child grow taller than predicted?
Yes. Predictions describe likely outcomes, not limits. Nutrition, sleep, overall health and the timing of puberty all affect final height. Children who start puberty late often grow taller than their percentile suggested.
When should I talk to a doctor about my child’s height?
See a pediatrician if your child is below the 3rd or above the 97th percentile, crosses two major percentile lines, grows less than about 4 to 5 cm (2 in) a year before puberty, or starts puberty very early or late.
Sources
- Tanner JM, Goldstein H, Whitehouse RH. Standards for children’s height at ages 2–9 years allowing for height of parents. Archives of Disease in Childhood. 1970;45:755–762.
- Fryar CD, et al. Anthropometric Reference Data for Children and Adults: United States, 2015–2018. NCHS, 2021.
- Silventoinen K, et al. Heritability of adult body height: a comparative study of twin cohorts in eight countries. Twin Research. 2003;6(5):399–408.
Predictions are estimates for healthy children. They are not a medical assessment; talk to a pediatrician about any concern with growth.