Parents often are very curious about predicting their child's adult height. You can try to estimate it using one of the following methods: (1) Review your child's height growth curve with your pediatrician once your child is older than 2 years, and extrapolate it out to 18 years of age on the growth curve. (2) Try this: Girls are half of their adult height at 18 months of age, while boys are half of their adult height at 24 months of age. (3) If you like mathematical formulas, calculate this: For girls, take the father's height in inches and subtract 2.5 inches; then, add it to the mother's height in inches, and divide this sum by 2 to get a predicted height in inches. For boys, take the mother's height in inches and add 2.5 inches; then, add it to the father's height in inches, and divide this sum by 2 to get a predicted height in inches.