Honestly, I'm not close enough to FI to really be able to say. 2014 was the first year that I tracked my spending for an entire year, and when all the receipts were in, we had spent about $48,000. That would peg our number at about 1.2 million, but I think it would be stupid to assume that we actually need that much to retire.
Almost $13,000 was housing expenses, and that number was inflated due to paying rent + mortgage for 3 months in the middle of a move. I doubt I will retire without a paid-off house anyway, so taxes and insurance would be our only housing costs post-FIRE. Health care cost us more than $10,000 last year, because my son has spina bifida. We would qualify for ACA subsidies and possibly other programs post-FIRE, which would bring this number down considerably. So now we're down to less than $30,000 in spending that we would need to support.
But I also anticipate that I'll earn income post-FIRE that won't come from our nest egg. I was pleasantly surprised to learn that I netted over $4300 last year from my hobby (woodworking). And that was with very little free time (full-time job + two kids under three). I was less surprised to find that over $2000 of our expenses were covered by credit card/bank rewards programs.
So, if I assume ~$30,000 in spending and ~$6,000 in miscellaneous income per annum, that means I need $600,000 in invested assets, plus a paid-off house, to be FI. Essentially identical to the MMM plan.
Ultimately, my plan is simply to stash as much as I can until I hit $500,000, then re-evaluate my spending and needs. There is no way I would consider myself FI with less than that.
