Height Calculator
Predict a child's adult height from the parents' heights with the mid-parental (Tanner) method used in pediatrics — including the likely range.
“How tall will they be?” is one of the oldest questions parents ask, and pediatrics has a standard first answer: the mid-parental height, published by James Tanner in 1970 and still used in clinics as the genetic target on growth charts. This calculator computes it, with the honest range around it.
The mid-parental method
Average both parents’ heights, then adjust for the child’s sex — the 13 cm (5 in) adjustment being the average height difference between adult men and women:
- Boy: (mother’s height + father’s height) ÷ 2 + 6.5 cm
- Girl: (mother’s height + father’s height) ÷ 2 − 6.5 cm
Around 95% of children finish within ±8.5 cm (about 3.3 in) of this target. The calculator shows that full range, because a single number would overstate what parental heights alone can tell you.
Why the range is wide — and what narrows it
Height is one of the most heritable human traits (~80% genetic), but it’s set by thousands of gene variants shuffling in each child, plus nutrition, health, and puberty timing. That’s the spread in the ±8.5 cm. Clinicians narrow the prediction with information this calculator doesn’t ask for: the child’s own growth-chart percentile (children tend to track their line), and, when precision matters, a bone-age X-ray.
When to ask a pediatrician
The prediction is for curiosity and planning; the growth pattern is what matters medically. A child steadily tracking any percentile — 10th or 90th — is generally growing well. Crossing two or more percentile lines downward, growth under 4 cm/year in mid-childhood, or a child far below the parental target range are the patterns worth a clinical look.
Frequently asked questions
How is a child's adult height predicted?
The mid-parental (Tanner) method averages the parents' heights and adjusts for sex: add 6.5 cm (2.5 in) for a boy, subtract 6.5 cm for a girl. Most children end up within about ±8.5 cm (3.3 in) of that target — the range the calculator shows.
How accurate is the prediction?
It estimates genetic potential, not destiny — about 95% of children land inside the ±8.5 cm range, which is admittedly wide. Methods that add the child's current measurements (like bone age or growth-chart tracking) narrow it, which is what pediatricians use when precision matters.
Does doubling a child's height at age 2 work?
It's a rough folk rule with some basis — children have reached roughly half their adult height around age 2 (boys) or 18 months (girls) — but it's less reliable than the mid-parental method and much less reliable than growth-chart tracking.
What besides genetics affects final height?
Genetics sets most of it (about 80%), but nutrition, chronic illness, sleep, and puberty timing shape the rest. A child consistently tracking a percentile line on their growth chart is the reassuring pattern; crossing multiple lines downward is what warrants a pediatrician's look.