Child Height Predictor
Estimate how tall your child will be as an adult, as an honest range: the research-based Khamis-Roche method plus the classic parent-height formula.
Your result will appear here
Enter your child's age and both parents' heights, then press Predict Adult Height.
How Tall Will My Child Be? What an Honest Answer Looks Like
No formula can name your child's adult height to the centimeter, and any calculator that prints a single confident number is hiding its uncertainty. What a good prediction can do is narrow the answer to a realistic range. This tool uses the Khamis-Roche method, published in the journal Pediatrics and widely used to estimate adult height without a bone-age X-ray, and shows the published error band as part of the result, not as a footnote. The classic parent-height formula is calculated alongside so you can see how the two compare.
Average Height by Age
For context around any prediction, this is the median height of American children at each age on the CDC growth charts, and how much of the median adult height (about 176.8 cm for men, 163.3 cm for women at age 20) has been reached:
Two things stand out. Girls are ahead of boys in percent-of-adult terms at every age (they mature earlier and finish sooner), and by age 10 the median boy has already reached about 79% of adult height, the median girl about 85%. A child tracking above or below these medians is not "ahead" or "behind" in any meaningful sense - these are population midpoints, not targets.
How the Khamis-Roche Method Works
The method comes from the Fels Longitudinal Study, which measured the same children year after year into adulthood. For each half-year of age from 4 to 17.5, the researchers fitted an equation that weighs three inputs: the child's current height (the strongest signal), current weight (a hint about build and how far along growth is), and the average of the parents' heights (the genetic baseline). The weights shift with age, and by the late teens the child's own height dominates the equation almost entirely, which matches common sense: the closer a child is to adulthood, the more their current height already tells you.
Worked Example
Take a 10-year-old boy who is 137 cm (4 ft 6 in) tall, weighs about 32 kg (70 lb), with a 162.5 cm (5 ft 4 in) mother and a 178 cm (5 ft 10 in) father:
- Parent average: about 170 cm (5 ft 7 in)
- Khamis-Roche estimate: about 176 cm (5 ft 9.5 in)
- 90% band: roughly 171 to 182 cm (5 ft 7.5 in to 5 ft 11.5 in)
- Mid-parental estimate for comparison: about 177 cm, give or take 10 cm
The two methods happen to agree closely here. When they disagree, the Khamis-Roche figure is the one to trust - it can see how this particular child is growing, while the parent formula only knows the family average.
The Mid-Parental (Tanner) Formula
The formula clinicians use for a quick first look at genetic target height: average the parents' heights, then add 6.5 cm (2.5 in) for a boy or subtract 6.5 cm for a girl. Most children reach an adult height within about 10 cm (4 in) of that figure. This tool falls back to it automatically for children under 4, or when you leave the child's measurements empty.
Accuracy, Stated Plainly
In the source study, 90% of boys ended up within about 5.3 cm (2.1 in) of the Khamis-Roche prediction and 90% of girls within about 4.3 cm (1.7 in); half landed inside a band less than half that wide. Predictions are least certain around puberty, when growth timing differs most between children. One limitation the calculators that use this method rarely mention: the equations were developed on white American children from the Fels study. The math still produces a reasonable estimate for children of other backgrounds, but the published accuracy figures were not measured there, so the band should be read a little wider.
What This Tool Deliberately Does Not Do
It does not chart your child's percentile or track growth over time; that is a different question, answered properly by the Growth Tracker on WHO standards (ages 0-5) or by your pediatrician's growth chart at any age. It does not diagnose anything: no estimate here can tell you whether growth is normal, and no product or exercise can add to what genetics and healthy development provide. If your child seems to be growing much slower or faster than peers, or has crossed percentile lines on their growth chart, that is a conversation for your pediatrician, not a calculator.
Frequently Asked Questions
How tall will my child be?
The most reliable everyday estimate comes from the Khamis-Roche method, which combines your child's age, current height, current weight and both parents' heights. It was published in the journal Pediatrics and needs no X-rays. The result is a range, not a single number: in the source study, 90% of children ended up within about 5.3 cm (2.1 in) of the prediction for boys and 4.3 cm (1.7 in) for girls.
How accurate is the Khamis-Roche method?
It is among the most accurate published methods that do not require a bone-age X-ray. In the original study, half of the children ended up within about 2.2 cm (boys) or 1.7 cm (girls) of the prediction, and 90% within about 5.3 cm (boys) or 4.3 cm (girls). Accuracy is lowest in early puberty, when growth timing varies most. The equations were developed on white American children from the Fels Longitudinal Study, so for other backgrounds the published accuracy figures are less certain.
How does the Khamis-Roche method work?
It is a statistical model built from decades of growth data. For each half-year of age from 4 to 17.5, it weighs three things - your child's current height, current weight and the average of the parents' heights - and combines them into an adult height estimate. Current height matters most; weight helps signal how far along in growth a child is; parent heights carry the genetic baseline.
How accurate is the mid-parental height formula?
The mid-parental (Tanner) formula averages the parents' heights and adds 6.5 cm (2.5 in) for a boy or subtracts 6.5 cm for a girl. It is a rough genetic target with a margin of error of about 10 cm (4 in), because it knows nothing about the child. It is still useful under age 4 or when the child's measurements are unknown, and clinicians use the same formula as a first look at a child's genetic target height.
Does height at age 2 predict adult height?
A popular rule of thumb doubles a child's height at age 2 (or at 18 months for girls) to estimate adult height. It is only a rough approximation - it has no published error band and tends to overestimate for early-maturing children. A method that uses more information, like Khamis-Roche from age 4, gives a more dependable range.
Can a child be taller than both parents?
Yes. Height is shaped by many genes from both sides of the family, plus nutrition and overall health, so children regularly end up taller (or shorter) than either parent. That is exactly why every serious prediction method returns a range rather than a promise.
At what age do children stop growing?
On the CDC growth charts, the median girl has nearly finished growing by about age 15 (gaining less than 2 cm after that), while the median boy keeps growing until about 17-18. Individual timing varies with puberty: early developers finish sooner, late developers keep growing longer.
Why does the predictor ask for my child's weight?
Weight is one of the three predictors in the Khamis-Roche equations, alongside current height and parent heights. It carries a small signal about body build and how far along in growth a child is, which sharpens the estimate. It is used only inside the calculation - the tool makes no comment about weight itself.
Related Reading and Tools
- Growth Tracker: today's height and weight on WHO percentile charts (ages 0-5)
- Baby BMI Calculator: where your young child's BMI falls on WHO standards
- Child Calorie Calculator: daily energy needs for ages 1-18, from age, size and activity
- Child Development Stages: From Birth to 18
- Kids' Healthy Eating Guide
Methodology and Sources
Adult height estimates use the Khamis-Roche method (Khamis HJ, Roche AF, "Predicting adult stature without using skeletal age: the Khamis-Roche method", Pediatrics 1994;94:504-507), with the corrected coefficients from the 1995 erratum (Pediatrics 1995;95:457) - the version of the tables that matters, since the originally printed weight coefficients contained errors. The parent-based estimate is the standard mid-parental (Tanner) target height formula. Median heights by age come from the CDC Growth Charts data files (stature-for-age, 50th percentile). The calculator runs entirely in your browser; none of the heights or weights you enter are sent anywhere unless you choose to save them to your account.
Important Considerations
These estimates describe statistical patterns in healthy children, not your individual child, and they cannot detect or rule out any medical condition. Children with a chronic illness, endocrine condition or significantly early or late puberty fall outside what these formulas were built on. For any concern about growth, the right first step is your pediatrician, who can measure properly, plot trends over time and refer for evaluation if needed.