Except that me saying the amount is dependent on your situation is leaving some margin for if your child is special needs or you're going through a divorce or taking care of elderly parents or things of that nature where you'd probably want to decrease your risks by increasing the 12 months to 18 months to account for more unknowns that wouldn't apply to other people, for example. I do not consider it to be simple math nor a matter of an absolute right/wrong stance.