How Tall Will My Child Be?
Two things predict a child's adult height reasonably well: their parents, and the line they've been tracking on the growth chart. This page covers both — the formula, how to read percentiles without panicking, the rules of thumb that don't work, and the specific patterns that mean it's time to call a paediatrician.
The formula: mid-parental height
Average both parents' heights, then adjust for sex:
| Child | Estimated adult height |
|---|---|
| Boy | (father + mother) ÷ 2 + 6.5 cm (+2.5 in) |
| Girl | (father + mother) ÷ 2 − 6.5 cm (−2.5 in) |
This gives a single number, but the honest output is a range: roughly ±5 cm around it for most children. The calculator above combines this with your child's current height for their age, which sharpens the estimate — particularly for children who sit well away from the average.
Reading the growth chart properly
A percentile compares your child with 100 children of the same age and sex. The 25th percentile means 75 of those 100 are taller. Parents routinely misread this as a grade. It isn't.
The percentile number matters much less than the shape of the line. A child steadily on the 10th percentile is growing normally. A child who slides from the 75th to the 25th over two years needs looking at — even though 25th is the "better" number.
Children find their genetic channel in the first two to three years of life and then tend to stay in it until puberty. That is what a healthy chart looks like: one line, followed consistently, then a spurt.
Patterns that are normal
- Tracking a low percentile steadily — usually just short parents.
- Channel-finding before age 3 — babies commonly shift percentiles early as birth size gives way to genetics.
- Falling behind peers at 12–13, then catching up — classic late puberty, especially in boys.
Patterns worth a doctor's visit
- Growth under 4 cm per year between age 4 and puberty.
- Crossing downward through percentile lines after age 3.
- Height far below what the mid-parental estimate predicts, with no family explanation.
- No puberty signs by 13 (girls) or 14 (boys) — or puberty starting before 8 (girls) / 9 (boys).
The conditions doctors screen for at this point — thyroid disorders, growth hormone deficiency, coeliac disease, chronic illness — are treatable, and treatment works far better while the growth plates are still open.
Rules of thumb that don't hold up
- "Double their height at age 2." Rough at best. It's reasonable for boys, overestimates for girls, and completely ignores how tall the parents are.
- "Big feet mean a tall adult." Feet finish growing before the spine and legs do, which is why teenagers hit adult shoe size early. It signals timing, not final height.
- "Sport makes children taller." Activity supports healthy bone development. It does not raise the genetic ceiling — and heavy training combined with under-eating can work in the opposite direction.
The 20% you can influence
About 80% of adult height is genetic. The remaining share isn't a lever for exceeding your child's potential — it's what stops them from falling short of it:
- Sleep — growth hormone is released in its largest pulses during deep sleep. School-age children need 9–11 hours, teenagers 8–10.
- Nutrition — enough protein, calcium, vitamin D and total calories, particularly through the growth spurt when demand spikes.
- Treating what's treatable — the single biggest avoidable loss of height comes from an undiagnosed condition running for years.
↑ Run the free predictor for your child — 60 seconds, result shown without an account.
Frequently asked questions
How can I predict my child's adult height?
Use the mid-parental method: average both parents' heights, then add 6.5 cm for a boy or subtract 6.5 cm for a girl, and combine it with where your child currently sits for their age. Together the two usually land within about 5 cm of the real outcome.
Is doubling height at age 2 accurate?
It's a rough rule of thumb, not a prediction. It works reasonably for boys, overestimates for girls, and ignores parental height entirely. Mid-parental is more accurate for any child past toddlerhood.
What does my child's percentile mean?
It compares your child with other children of the same age and sex — the 25th percentile means 75 out of 100 are taller. A low percentile isn't a problem in itself; consistently tracking one line is the healthy sign, whichever line it is.
When should I see a doctor about my child's height?
If growth is under about 4 cm a year between age 4 and puberty, if your child crosses downward through percentile lines, if they're far below the mid-parental estimate with no family explanation, or if there are no puberty signs by 13 in girls or 14 in boys.
Can anything make my child taller?
Nothing raises the genetic ceiling, but adequate sleep, sufficient protein and calories, and normal activity help them reach it. Supplements and stretching devices don't add bone. Where a medical cause exists, treating it protects growth — which is why early assessment matters.
This tool provides a statistical estimate for general information only. It is not medical advice, diagnosis or treatment. If you are concerned about your child's growth, speak to a paediatrician or family doctor.