Comment by geekster777

Honestly, I've been hand waving this somewhat. We'll be on my wife's insurance for the next several years at least, and live in an area where public schools are quite good (Massachusetts). My assumption is that each kid will add ~$15k in cost a year, though I could be underestimating this. I'm planning a few layers of buffer here. 1) My wife wants to keep working past 6 years from now and has no interest in FIRE (this is huge, but 6 years is a long time for her to change her mind). 2) Once kids are old enough for elementary school, I can go back to work. If my math is wrong, 7ish years of overspending shouldn't set back our FIRE too considerably. 3) Being a stay at home dad to start should seriously eliminate the expensive childcare costs. 4) My FIRE numbers don't include my 401k/IRAs, which I can dip from (with penalties) if necessary.