Is it true that if you double your height at 2 years old that that is how tall you will ultimately be?

Height prediction: Doubling a 2-year-old's standing height is one way of predicting one's height. Another method is, to add father's and mother's heights in inches and divide by 2. Then, for boys - add 2.5 ins; for girls, subtract 2.5 inches.

Not reliable: Doubling the height of a 2 yo toddler doesn't predict final height very well, particularly these days with obesity. Factors including weight, pubertal timing and genetics are far more important.