Why Affluent Couples Are Converting $1.4M 401(k)s Into Roth Accounts Before Age 73
The decade between retirement and required minimum distributions looks like a quiet stretch, but for couples sitting on seven-figure 401(k)s, it is a closing window with a tax bill attached to every year they wait.
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A recent thread on r/retirement captures the tension well. 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. 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 balance by 26.5, producing a mandatory withdrawal near $100,000 in year one, with the amount 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 confirmed by IRS Revenue Procedure 2025-32, 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. Those rates are now locked in beyond 2026 after the One Big Beautiful Bill Act (signed July 2025) made the Tax Cuts and Jobs Act bracket structure permanent, eliminating the sunset risk that once made multi-year Roth planning feel uncertain.
Federal tax on that stack runs 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 well below the 22% to 24% blend they would otherwise 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 $81 per person per month on top of the $202.90 standard Part B premium. Cross the next tier and the total premium climbs past $400 per person. The 22% bracket ceiling at $211,400 of taxable income sits neatly below that first IRMAA cliff, and planners who miss that alignment by even a single dollar trigger a full year of surcharges.
One exception is worth exploiting. Conversions done during the calendar year each spouse turns 62 never affect a future IRMAA premium, because that year falls outside 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 has climbed to roughly 5%, its highest level since July 2007, as persistent inflation and growing fiscal concerns drive yields higher. Markets, as of mid-September 2026, were pricing in roughly a 92% probability of a quarter-point rate hike at the Federal Reserve’s September meeting, which would push the fed funds target range above its current 3.50% to 3.75% band. That combination of rising long yields and tighter short rates means the real cost of delay on a 401(k) conversion is compounding in two directions at once: the untaxed balance is growing faster in nominal terms, while the purchasing power of a future RMD stream is eroding.
Today’s brackets and the enlarged standard deduction are known quantities. Waiting locks in nothing except the government’s option to move the goalposts in future legislative cycles.
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 from the 401(k) itself. Using retirement dollars to settle the tax bill defeats the strategy by shrinking the balance that would otherwise compound tax-free for the rest of both lives and, eventually, for heirs.
Editor’s note: This article has been updated to reflect the 10-year Treasury yield rising to approximately 5% as of mid-September 2026 (its highest level since July 2007) and to correct the first-tier IRMAA Part B surcharge to roughly $81 per person per month (up from the previously stated $75), based on the confirmed 2026 standard premium of $202.90 and first-tier total premium of $284.10.
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Marc Guberti is a personal finance writer who has written for US News & World Report, Business Insider, Newsweek and other publications. He also hosts the Breakthrough Success Podcast which teaches listeners how to use content marketing to grow their businesses.
