Why do I focus on expense-based planning in my book? For the simple reason that our primary goal is to make sure we can pay for our basic living costs during those extra decades (what I call our Longevity Cost). The only way to do that is to look at what we are spending now and then project that into the future! You can't do it by income. My income may be higher, lower, or may not exist when I get ready to retire, but my expenses will likely continue To me, using the expense-based approach is the only way to do that because it's the variable that you can control, for the most part.

Check out Chapter 4 "Do the Math" in my book for more details about the expense-based approach to planning and also how you can use Quicken to do that. I also address some of the issues with using those online retirement calculators and the errors than can result from them!