About the Height Predictor
Adult height is roughly 80% genetic. The classic mid-parental method averages the parents' heights and adjusts by 6.5 cm for the child's sex.
- Boy: mid-parent + 6.5 cm
- Girl: mid-parent − 6.5 cm
For school-age children, the calculator also adds a simple growth-extrapolation estimate using approximate WHO/CDC ratios — useful as a sanity check on the genetic figure. This calculator is free to use and all calculations run entirely in your browser.
Worked example: a boy with a 180 cm father and 165 cm mother
Using the calculator's default figures — a boy, father 180 cm, mother 165 cm, currently age 10 and 140 cm tall — the result is:
| Result | Estimate |
|---|---|
| Mid-parental height ((180 + 165) ÷ 2 + 6.5) | 179.0 cm |
| Likely range (± 8 cm) | 171.0 – 187.0 cm |
| Growth extrapolation (140 cm ÷ 0.77 at age 10) | 181.8 cm |
| Predicted adult height · current percentile | 179.0 cm · 55th |
Switch to a girl, change the parents' heights or enter your child's current age and height to see how the prediction shifts.
Average Percentage of Adult Height Reached by Age
Children reach a fairly predictable share of their final adult height at each age. Dividing a child's current height by the fraction below gives the growth-based estimate this calculator uses.
| Age | Boys | Girls |
|---|---|---|
| 2 years | 49% | 50% |
| 5 years | 62% | 63% |
| 8 years | 72% | 74% |
| 10 years | 77% | 82% |
| 12 years | 83% | 92% |
| 15 years | 96% | 99% |
| 18 years | 100% | 100% |
Girls mature earlier, so they reach each percentage sooner and finish growing earlier than boys.
What affects accuracy
- Timing of puberty (early or late onset by 1–2 yr can shift adult height by 3–5 cm)
- Nutrition during the first 5 yr and during adolescence
- Chronic illness or growth disorders
- Step-parents or unknown biological parents — use biological parent heights for accuracy
Frequently Asked Questions
How accurate is the mid-parental method? It is accurate to within about ± 8 cm (around 3 in) for most children. Genetics is the dominant factor, but nutrition, illness and the timing of puberty can shift the final result.
What is the mid-parental formula? Boy: ((father + mother) ÷ 2) + 6.5 cm. Girl: ((father + mother) ÷ 2) − 6.5 cm. The 6.5 cm reflects the average difference in adult height between the sexes.
Why does current child height matter? For school-age children you can also project adult height by extrapolating their current height for their age. Combining the genetic and growth-based estimates gives a more reliable range.
Can I influence height? Genetics accounts for about 80%. The remaining 20% is mostly nutrition (especially in the first 5 years), sleep and overall health. Beyond these, no commercially available product reliably increases final adult height.
At what age do children stop growing? Most girls reach their adult height around 14–16, roughly 2 years after their first period, and most boys around 16–18. Growth slows sharply once the growth plates close at the end of puberty.
± 8 cm range — why so wide? Even with both parents' heights known, the genetic spread plus environmental factors give roughly a 16 cm prediction interval at 95% confidence.
Can a child be taller than both parents? Yes — common when one parent comes from a tall family with shorter immediate parents. Genetic recombination is unpredictable.
Last reviewed: June 2026. Estimates based on the mid-parental method and average growth ratios — not medical advice. Consult a paediatrician for a clinical growth assessment, especially if a child's growth deviates from family norms.