A 12% Roth Conversion Window Closes at RMD Age 73

The strategy fits someone retired before 73 with meaningful pretax IRA or 401(k) balances, a reasonable expectation that RMDs and Social Security will lift later income into a higher bracket, and a way to pay the conversion tax from a taxable brokerage account. Paying with IRA dollars shrinks the balance that would otherwise compound tax-free, which defeats the point of the move. The strategy is a poor fit for someone already in the top bracket who expects a lower bracket later, or for someone who would need to sell IRA assets or tap the converted money within five years to cover the bill.

Each conversion starts its own five-year holding period before earnings can come out tax-free, and the clock is tracked separately for each conversion. Medicare creates a separate problem. A large conversion raises modified adjusted gross income, and the two-year lookback means a 2026 conversion sets the Part B and Part D premiums paid in 2028. The 2026 IRMAA brackets start adding surcharges for joint filers above $218,000 in MAGI, with the top surcharge at $750,000 adding as much as $487 a month on Part B. Social Security adds another layer. Extra conversion income can push provisional income over the 85% threshold, which makes more of the benefit taxable. A retiree already collecting Social Security should model that before converting.

The 2027 Social Security COLA is tracking toward 3.1%, so benefit checks and later RMDs both keep climbing. The RMD clock for account owners born between 1951 and 1959 starts at 73.