A recent thread on r/retirement captures the tension. A 62-year-old planning to retire in two years asked whether Roth conversions were worth the effort, hoping to lower overall taxes in my lifetime, eliminate or reduce taxes for a surviving spouse. The replies converged on a single point: the gap between retirement and required minimum distributions is the most valuable tax-planning window most affluent couples ever get, and most of them waste it.
Consider a couple, both 62, both retired, with $1.4 million in a traditional 401(k) and no pensions or Social Security yet. They have 11 years before RMDs begin at age 73, and their taxable income right now is close to zero. That combination is a countdown.
Why Standing Still Is the Expensive Choice
At a 6% growth rate, $1.4 million compounds to roughly $2.7 million by age 73. The first RMD under the IRS Uniform Lifetime Table divides that by 26.5, producing a mandatory withdrawal near $100,000 in year one and rising every year after. Layer in two Social Security checks by then, and up to 85% of those benefits becomes taxable. The couple lands in the 22% or 24% bracket for life, with IRMAA surcharges stapled to every Medicare premium.
Every dollar left in the 401(k) is a dollar that will come out on the IRS’s schedule, not theirs.
The Bracket-Filling Play
Under 2026 rules, a married couple filing jointly pays 10% on the first $24,800 of taxable income, 12% up to $100,800, and 22% up to $211,400. Add the $32,200 standard deduction and the household can generate $243,600 in gross income and stop at the top of the 22% bracket.
Federal tax on that stack: about $35,932, an effective rate near 15% on the conversion itself. Convert $243,600 per year for seven years and the couple moves roughly $1.7 million of pre-tax money into a Roth, enough to drain the current balance and its growth. The lifetime federal bill lands around $250,000, all paid at rates lower than the 22% to 24% blend they would face on forced RMDs stacked on top of Social Security.
The IRMAA Trap That Kills Sloppy Conversions
Medicare’s income-related monthly adjustment amount uses a two-year lookback. Income at age 63 sets the Part B premium at age 65. For 2026, a couple crosses the first IRMAA tier when modified adjusted gross income exceeds $218,000, adding roughly $75 per person per month on top of the $202.90 standard Part B premium. Cross the next tier and it climbs past $200 per person. The 22%-bracket ceiling at $211,400 taxable income sits neatly below that first IRMAA cliff, which is not a coincidence and should not be crossed by accident.
One exception is worth exploiting. Conversions done during the calendar year each spouse turns 62 never touch a future IRMAA premium, because that year is off the two-year lookback by the time Medicare starts at 65. That is the year to run a larger conversion, potentially filling the 24% bracket up to $403,550 of taxable income.
Why the Rate Environment Argues for Now
The 10-year Treasury sits near 4.57%, the fed funds upper bound is 3.75%, and core PCE inflation continues to grind higher, with the index at 130.08 in May 2026 versus 126.43 a year earlier. Persistent inflation erodes the real value of a future RMD stream while today’s brackets and the enlarged standard deduction are known quantities. Waiting locks in nothing except the government’s option to move the goalposts after the 2028 election cycle.
Three Moves for This Quarter
- Model the year-62 conversion aggressively. With no IRMAA lookback yet in play, run a projection that fills the 24% bracket up to $403,550 of taxable income. For most couples this will be the single most tax-efficient conversion year of their retirement.
- Cap every subsequent year at $211,400 of taxable income. That ceiling parks the household inside the 22% bracket and beneath the $218,000 IRMAA threshold, keeping Medicare premiums at the standard $202.90 once the two-year lookback engages at 65.
- Pay the conversion tax from a taxable brokerage account, never the 401(k) itself. Using retirement dollars to settle the tax bill defeats the strategy by shrinking the balance that ends up compounding tax-free for the rest of both lives and, eventually, for heirs.
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