How this calculator works
The mid-parental height method averages both parents' heights, then adjusts for the average height gap between men and women (about 13 cm), giving a target height with a normal range around it.
- father, mother — each parent's height in cm
- 13 — average adult height gap between sexes (cm)
More detail
What the ± range means
The predicted number is a target, not a guarantee. The ±8.5 cm band used here is Tanner's classic figure for the 3rd-97th percentile range. Tanner himself later widened it (±9 cm for girls, ±10 cm for boys), and 95% confidence intervals derived from modern CDC growth charts are wider still (±10.6 cm for girls, ±11.7 cm for boys) — so treat ±8.5 cm as the narrowest of the published estimates, not the outer bound.
Keep in mind. This formula estimates genetic potential only. Chronic illness, malnutrition, or poor sleep during childhood and puberty can shift actual adult height below this estimate, regardless of parental height.
Frequently asked questions
How accurate is the mid-parental height method?
It is a rough estimate, not a precise forecast. The ±8.5 cm band shown beside the result is Tanner's classic figure and it is the narrowest of the published estimates — Tanner himself later widened it to ±9 cm for girls and ±10 cm for boys, and 95% confidence intervals from modern CDC growth charts run to ±10.6 cm for girls and ±11.7 cm for boys. Read it as 'at least this wide, possibly wider', not as an outer bound.
Why is 13 cm added for boys and subtracted for girls?
13 cm approximates the average adult height difference between men and women. Adding it for boys and subtracting it for girls converts the parents' average height into a same-sex target.
Can a child end up outside the predicted range?
Yes. The formula only reflects genetics from height; nutrition, sleep, chronic illness, and puberty timing can all push actual adult height outside the estimated range.
Is this calculator a medical tool?
No. It's a statistical estimate for general interest, not a diagnostic tool. If you have concerns about a child's growth, a pediatrician can track growth curves properly.