[breischl]

25x is another way of stating the commonly-cited 4% Safe Withdrawal Rate. It wasn't invented by MMM, it's from the well-researched Trinity Study[1].

If you're planning on a higher withdrawal rate you're probably heading for trouble. One big market downturn and you'll end up eating so much capital that you won't be able to recover. It's sort of like playing blackjack without a sufficiently large bankroll - if you hit one bad run of luck you're done even if you should've won according to the averages. A good way of visualizing this is playing with numbers at FireCalc[2].

[1] - http://en.wikipedia.org/wiki/Trinity_study [2] - http://www.firecalc.com

[skorgu]

Thanks for Firecalc! Saves me from having to build it myself.