The mid-parental height method
Height runs in families, so the parents' heights are the starting point for most estimates. The mid-parental method, also called Tanner's formula, averages the two after adjusting for the difference between men and women:
| For a | Formula |
|---|---|
| Boy | (mother's height + father's height + 5 in) ÷ 2 |
| Girl | (mother's height + father's height − 5 in) ÷ 2 |
In centimeters, use 13 cm instead of 5 inches. A mother of 5 ft 3 in (63 in) and a father of 5 ft 9 in (69 in) give an estimate of 68.5 in, or 5 ft 8½ in, for a son and 63.5 in, or 5 ft 3½ in, for a daughter. The AAP describes this as a very rough estimate with a margin of error of about 4 inches up or down, which is the range the calculator shows.
The doubling rule
Babies and toddlers grow fast, and by the second birthday a child has done roughly half their growing. That's the idea behind doubling a boy's height at 2 years, or a girl's at 18 months, since girls develop sooner. The AAP calls it a popular rule of thumb rather than a medically validated prediction tool, so treat the result as a fun comparison, not a forecast.
What else decides how tall a child grows
Genes set most of the range: studies suggest 60% to 70% of the differences in height come from the parents. Within that range, the AAP lists the things that matter:
- Nutrition. Too few calories, too little protein or missing vitamins and minerals can slow growth.
- Sleep and activity. Sleep patterns, physical activity and overall well-being all affect growth.
- Hormones and health. Low thyroid or growth hormone, long-term conditions such as untreated celiac disease, and some long-term medications can slow growth.
- Puberty timing. Children who start puberty early often have their growth spurt sooner and may stop growing earlier.
How pediatricians track growth
At each well-child visit, your pediatrician plots height, weight and head size on a growth chart and compares them with earlier visits. A child who keeps following their curve is likely to end up within their expected genetic range. For babies under 2, you can see the same comparison with our baby percentile calculator. If you're worried about your child's growth, ask your pediatrician: a hand and wrist X-ray (bone age) gives the most accurate prediction, and growth problems are easier to treat when found early.