Bud Hebeler uses a similar approach...
... in the back of his "J.K. Lasser's Your Winning Retirement Plan" book.
Try a library copy and see if it's worth just using a spreadsheet. It can even be done with John Galt's pencil, envelope, & calculator.
The book written on E-R.org, "The Military Guide to Financial Independence and Retirement", on sale now! For more info see "About Me" in my profile.
I don't spend much time here anymore, so please send me a PM. Thanks.