Originally Posted by accountingsucks
I think it is fairly accurate as I have diligently tracked my expenses for awhile now and my sources of income are known and predictable.*
You will be lucky indeed for this assumption to remain true for the next 20 years.
However, it got me thinking, and looking back I have used a spreadsheet that I started in 1993 doing similar to what you are doing and tracked target salary and target 401(k) savings against what I predicted for that salary. I assumed contributing the max, a 10% return and salary increases of 7% each year. In 13 years I am only off by a mere 1.5% - amazing really as these days I use all the sophisticated planning tools available to me on line.
The bigger picture had my wife going back to work and earning a good salary, good luck in real estate etc so I am actually far better off in total than I could have imagined, but in tracking that single salary it has remained remarkably close to my optimistic aims.