Social Security is not factored in here, as I do not expect Social Security to exist in 2040. But if it does, CHA-ching! Don't worry, though. I have a plan*: Mega Millions, here I come.
*Really though, don't worry about it (especially if you're related to me and think I'm going to show up on your doorstep, hat in hand, when I'm in my dotage). I'm significantly upping my contributions as the Boy meanders toward school and away from full-time daycare. The cost of two kids in daycare full-time takes bite out of my income, yo.