The taxes are due in the year you convert at your regular income-tax rate. If you move a large sum all at once that can bump you into a higher tax bracket. Converting in smaller amounts for several years is a wise move, but even then your income will be higher every year. Because taxes are progressive, you end up paying your highest personal tax rate on those converted IRA dollars.
Many people retire in their late 50s or early 60s, years before RMDs begin, which creates a window of time where tax planning opportunities abound. […] Actively engaging in tax planning can boost your after-tax income in retirement by a meaningful amount.
With lower rates now, you can engage in tax arbitrage.