babycenter.com height predictor:

Your girl will likely be 5 ft. 7 in. at age 18.
Your boy will likely be 6 ft. 4 in. at age 18. (whoa, dude....)

This prediction is a "best guess" but it's still just that -- a guess. Based on the formula we used there is a 50 percent chance that your child's full-grown height will be within 0.7 inches (above or below) of this prediction, and a 90 percent chance that it will be within 1.7 inches.

What they left out was the part that goes "Your child will most likely be taller than you by the first grade..."