That 16 years is consistent with the right column of the analysis that I provided at post #32, which was 17 years... the negative cash flow of paying the tax is offset each year by avoiding tax on what was effectively transferred from the taxable account to the Roth. The disadvantage grow a little each year until RMDs begin at which point it is recovered over about 10 years.
That's comforting to at least confirm that the timeline Fidelity is suggesting seems reasonable. I went back into i-Orp and ran the model, and it's now suggesting that Roth conversions up to the 24% bracket will give us a slight advantage vs no Roth conversions. It won't even run the numbers for us at any lower brackets - I get a model error message. While it shows a small advantage for partial conversions, it isn't a compelling, life-changing advantage. Interestingly, a summary of i-Orp's research says that on average, Roth conversions yield about a 1% benefit vs not converting. I'm surprised it is so small.
Some missing things in the model analysis:
- As far as I can see, it doesn't allow one to compare the advantages of Roth conversions vs generating LTCG income in a taxable account.
- I've assumed we both live a similar life span so I suppose results would be different if I assumed one of us meets with an early demise. OTOH, since we already have plenty to fund our lifestyle for the rest of our lives based on the assumptions, if only one person were left, there may be a higher tax rate, but there would be lower expenses too.