What I have done is a projection model of all of our sources of retirement income from now until we are 90. So it includes interest on taxable account money, my small fixed pension, and SS. It also includes a cell for Roth conversions each year and for RMDs once I'm 73. And most importantly, it includes projected standard deductions, taxable income and income taxes based on today's brackets and rates. All values are adjusted for inflation and investment balances like IRAs are adjusted for growth and withdrawals.
With no Roth conversions, we would pay no taxes until I start RMDs but some standard deductions would go unutilized each year and once I start RMDs the effective tax rate on the RMDs would be ~25-27%. So if I do nothing then I'll pay 25-27% of the RMDs in tax.
With Roth conversions to the top of the 12% tax bracket we pay about 11.5% of the convertsion amount in tax now and the effective tax rate on RMDs one they start is ~17%.
I can also look at the total paid in tax from now to age 90... with conversions is $258k and without any future conversions is $326k... not life changing but worth a little effort.
Thanks for weighing in pb4uski. Is your projection model a spreadsheet that can be easily created? Please advise how I would start putting together this projection model?