Guide
Tanner’s 1970 formula: add the parents, add 13 cm for a boy or subtract 13 cm for a girl, then divide by two. The classic range is about ±8.5 cm.
It combines the child’s current stature percentile (CDC 2000), both parents (Tanner 1970 and Luo 1998), and Khamis–Roche when age is 4–17.5 and weight is entered. The headline number stays free. The $4.99 Full Growth Report adds the range, method split, growth window, and a printable page.
It does not lengthen bones, reopen growth plates, or replace a pediatrician. A falling percentile, delayed puberty, or chronic illness belongs in clinic.
More questions: How tall will my child be? · How tall will my son be? · How tall will my daughter be? · Khamis–Roche calculator · Mid-parental height calculator · Child height percentile · Adult height predictor · Can short parents have a tall child? · How accurate are height predictors? · Height for youth athletes