The Single Year of Roth Conversion That Saved a 64-Year-Old $312,000 Over a 20-Year Retirement

The setup: one quiet tax year before Social Security and Medicare lock in

A 64-year-old single retiree wrapped up her career in 2025 and now holds $1.6 million in a traditional IRA, $200,000 in a Roth, and $250,000 in a taxable brokerage account. She plans to delay Social Security until age 70, and Medicare coverage does not begin until 65. That makes 2026 a year with almost no taxable income arriving. The central question: leave the traditional IRA alone, or use the vacant bracket space to convert a substantial chunk to Roth?

The situation is more common than it may seem. Retirees in their early sixties routinely hit a narrow window where wages have stopped, Social Security has not started, and required minimum distributions (RMDs) remain a decade or more away. Drifting through that window without a plan carries a real, quantifiable cost.

The real tension: 24% now versus 22% to 24% later, plus IRMAA, plus state, for life

The 2026 single-filer tax brackets create a specific opportunity. The 24% bracket runs from $105,700 to $201,775 of taxable income, and the 32% rate takes over above that. The standard deduction for a single filer is $16,100. Converting $185,000 from the traditional IRA pushes her taxable income to $168,450, landing near the top of the 24% bracket while staying clear of the 32% threshold.

One notable wrinkle from the One Big Beautiful Bill Act: taxpayers age 65 or older can claim a new $6,000 senior deduction on top of the standard deduction for tax years 2025 through 2028. That deduction begins to phase out above $75,000 MAGI for single filers and is nearly exhausted by $175,000. At a $168,450 conversion MAGI, barely $393 of the $6,000 survives the phase-out. A full bracket-fill conversion effectively forfeits most of that senior benefit, which is one reason some advisors favor smaller annual conversions during this window.

Federal tax on the $185,000 conversion works out to roughly $33,276, paid from the brokerage account so every converted dollar reaches the Roth intact. The traditional IRA shrinks to roughly $1.42 million. Under SECURE 2.0, a retiree born in 1961 or 1962 faces an RMD starting age of 75, placing the first mandatory withdrawal roughly eleven years out. With 6% annual growth assumed over that period, the converted slice grows to approximately $352,000, tax-free for life.

The alternative path is more expensive. That same $185,000 left in the traditional IRA also grows to roughly $352,000 by RMD time, but every withdrawal is taxed at her future combined rate. Once Social Security income stacks on top, that rate will likely sit between 22% and 24% federally. With a median female life expectancy from age 73 of 16 to 17 additional years, cumulative federal tax on the unconverted path runs $90,000 to $110,000. Add $25,000 to $35,000 of Medicare IRMAA surcharges as her MAGI rises, plus roughly $15,000 of state tax at a 5% rate, and the conversion avoids $130,000 to $160,000 of direct lifetime tax. For context, roughly 5.1 million Medicare beneficiaries paid Part B IRMAA surcharges in 2025, and the 2026 entry threshold for single filers rose to $109,000 from $106,000 the year before, meaning more retirees than ever are crossing the line.

The compounding advantage is actually the bigger story. Roth balances carry no RMDs, so the converted slice keeps growing untouched. By age 90, that Roth portion reaches roughly $750,000 compared to $352,000 had it been drawn down on the IRA schedule, a gap exceeding $390,000. Total nominal lifetime value of the single-year decision lands between $300,000 and $340,000.

The three paths that actually move the number

1. Fill the 24% bracket once, this year. The conversion happens before Social Security begins, before RMDs arrive, and while the brokerage account can absorb the tax bill cleanly. This path suits retirees with a large traditional IRA, roughly a decade until RMDs, and outside cash to cover conversion tax. The trade-off: the $6,000 OBBBA senior deduction (available at 65) is largely eliminated by the elevated MAGI.
2. Smaller conversions spread across multiple years. Converting only within the 22% bracket each year from age 64 to 70 captures a lower rate but moves far fewer dollars before Social Security adds taxable income into the mix. Keeping MAGI below $75,000 each year also preserves the full $6,000 OBBBA senior deduction once she turns 65, a benefit worth up to $1,440 annually at a 24% rate through 2028. This approach weakens once Social Security begins and every conversion dollar stacks on top of benefit income.
3. Skip conversions entirely. Most retirees choose this path because writing a $33,000 check today stings more than ignoring a future obligation. The bill arrives regardless, spread across sixteen or more years of RMDs at higher combined rates with IRMAA attached. For a $1.6 million pre-tax balance, this is the most expensive choice by a wide margin.

What to act on first

Three rules govern the outcome. First, the conversion tax must be paid from outside the IRA. Using IRA dollars to cover the bill shrinks the converted amount and destroys most of the benefit. Brokerage or savings cash covers the check.

Second, factor in the IRMAA two-year lookback. A 2026 MAGI of $168,450 lands in IRMAA Tier 2 ($137,000 to $171,000 for single filers) for 2028 only, since Medicare uses income from two years prior. The 2026 IRMAA threshold for single filers sits at $109,000, meaning this conversion clears even the Tier 1 floor by a wide margin. That added premium is a real one-year cost and should be priced into the decision before the Medicare letter arrives. The standard Part B premium in 2026 is $202.90 per month; IRMAA surcharges add $81.20 to $487.00 per month on top of that, depending on which tier applies.

Third, watch the five-year clock on converted dollars. Each calendar-year conversion starts its own clock for tax-free treatment of earnings. At 64 with substantial liquidity elsewhere, this constraint rarely binds, but it deserves confirmation before locking in a six-figure conversion.

Editor’s note: This pass added context on the 2026 IRMAA entry threshold rising to $109,000 for single filers from $106,000 in 2025, the standard Part B premium of $202.90 per month, and the approximately 5.1 million Medicare beneficiaries who paid Part B IRMAA surcharges in 2025. Language and structure were tightened throughout for clarity.

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