I liked the approach taken by Guyton and Klinger in this paper, though I don't feel comfortable with the high initial SWR that they propose in later tables.
FPA Journal - Decision Rules and Maximum Initial Withdrawal Rates
I put together a spreadsheet (attached) to make it easier to determine the annual withdrawal using only the previous year's inflation, and value of portfolio at the beginning of the current year.
There is one assumptions made. a)The Capital Preservation Rule & the Prosperity Rule would not apply at the same time. Also, the Inflation Rule is used even though the paper seems to drop it in later calculations.
The spreadsheet has some example portfolio values to force the Capital Preservation Rule and the Prosperity Rule to come into play. It shows how your annual withdrawal as a percentage of portfolio self-corrects as your portfolio value goes up and down.
I would like your input on the spreadsheet. Is it correct? Useful? Suggestions to improve?