Child Height Predictor

A child height predictor estimates how tall a child is likely to be as an adult. Two different methods exist for this, and they trade off simplicity against accuracy in a very specific way: one uses only the parents' heights and works at any age, the other adds the child's own current stats and narrows the error margin substantially, but only within a specific validated age range¹,².

What This Calculator Measures

This estimates a child's likely adult height. It automatically uses whichever method fits the available data and the child's age, and tells you which one was used rather than leaving that invisible.

The Formula

Simple method (mid-parental height), usable at any age¹:

Boys = (Father's height + Mother's height + 13 cm) ÷ 2

Girls = (Father's height + Mother's height − 13 cm) ÷ 2

More accurate method, valid for ages 4.0 to 17.5 years. The published Khamis-Roche method predicts adult height from the child's current height, current weight, and mid-parent height². This calculator uses a simplified version of that idea:

Height-based estimate = current height ÷ average share of adult height reached at the child's age and sex

Predicted adult height = 0.7 × height-based estimate + 0.3 × mid-parental height

The average share comes from the CDC 2000 growth charts: the median height for the child's age and sex divided by the median height at age 20⁴. An average boy has reached about 58% of his adult height at 4 and 78% at 10, and an average girl about 62% at 4 and 85% at 10⁴.

You need to enter current weight for this method to run, but the number itself is built from current height and mid-parental height.

How This Calculator Computes Your Result

Enter both parents' heights, and the child's current age, height, and weight if you have them. If the child's age falls between 4.0 and 17.5 years and current stats are provided, we use the more accurate regression method. Otherwise, we fall back to the mid-parental method automatically and say so.

Why the Accuracy Gap Between the Two Methods Is So Large

Mid-parental height alone has a typical error margin of ±8 to 9 cm, useful as a rough baseline but wide enough that it isn't very precise for an individual child¹. The more accurate method narrows that to roughly ±5 cm², nearly half the error, because it's not just averaging two inherited numbers, it's using the child's own growth trajectory, current height and weight relative to their age, as additional evidence of how their individual growth is actually tracking, not just what their genetics alone would predict.

That ±5 cm figure describes the published method. The simplified version used here has not been tested on its own, so treat its margin as a guide rather than a guarantee.

A Worked Example

Say the mother is 165 cm (5 ft 5 in), the father is 178 cm (5 ft 10 in), and you leave the child's current stats blank.

• Boy: (178 + 165 + 13) ÷ 2 = 178 cm, about 5 ft 10 in

• Girl: (178 + 165 − 13) ÷ 2 = 165 cm, about 5 ft 5 in

With this method the calculator shows a typical error margin of ±8.5 cm (3.3 in), so the boy's likely range runs from about 169.5 to 186.5 cm and the girl's from about 156.5 to 173.5 cm. If you add an age between 4.0 and 17.5 plus current height and weight, it switches to the current-stats method, shows a margin of ±5 cm (2.0 in), and still lists the mid-parental height for comparison.

What the Prediction Means

The result is the middle of a range, not a target your child should reach. Height runs in families: if one or both parents are short, a child will most likely also be short, and most of the time there is no medical cause for short stature³.

The timing of growth varies too. Some healthy children are small for their age, start puberty later than their friends, and keep growing after most peers have stopped, often ending up about as tall as their parents. Doctors call this constitutional growth delay³. The current-stats method assumes an average timetable, so it can miss late or early developers.

To compare your child's height today with other children of the same age and sex, use the Child Growth Percentile Calculator.

Limits of the Methods

The Khamis-Roche method was developed from 223 boys and 210 girls in the Fels Longitudinal Study in southwest Ohio, all of them white, and its authors limit it to white American children without conditions that affect growth². It may be less accurate for children from other backgrounds.

When to Talk to Your Child's Doctor

Your child's provider checks growth at regular checkups by plotting height and weight on a growth chart and watching the growth rate over time³. Contact the provider if your child seems much shorter than most children their age, or seems to have stopped growing³. A prediction cannot show whether your child is growing normally. That takes measurements over time.