Every year or so I really get worried about how much I am saving, or indeed how much I am spending and I tend to go crazy checking Microsoft Money or whatever analysis tool I can get my hands on.
As most employees no longer have access to fixed retirements sponsored by their employer we are generally reliant upon 401k's and other retirement packages to help us figure out what to save. The problem is that with all these calculators is that you really do not know what your rate of return will actually be; you never know how long you will live and to a lesser degree you may not know what your income may be from year to year.
Calculating retirement funds for me always becomes a year to year affair, and so I try to find graphically appealing calculators to help in my decision making.
MSNBC has a good flash based calculator that I really like! no visible post back when you hit calculate.
You can mess with the numbers and figure out at what point your earnings from interest is more than you estimate you will spend...
Now that is the magic number!