The 11-Year Roth Conversion Window That Determines Your 73-Year-Old Tax Bill
A couple retiring at 62 with $1.5 million in a traditional 401(k) faces a critical tax decision. Without action, the balance grows to roughly $3 million by age 73, triggering a $113,000 required minimum distribution (RMD) that pushes them into high tax brackets and Medicare surcharges. By converting $90,000 to $100,000 annually into a Roth IRA between ages 62 and 70, they can reduce the first RMD to approximately $60,000, avoiding the 85% Social Security tax and IRMAA penalties.
Key points
- Under SECURE 2.0, RMDs begin at age 73. A $1.5 million traditional 401(k) compounding at 7% for 11 years reaches about $3 million, resulting in an initial RMD of roughly $113,000.
- This large RMD pushes taxable income into the 22% or 24% federal brackets, triggers taxation of up to 85% of Social Security benefits, and exceeds the 2026 IRMAA threshold of $218,000 for joint filers, adding $81.20 per person per month to Medicare Part B premiums.
- Converting $90,000 to $100,000 annually to a Roth IRA from ages 62 to 70 keeps taxable income within the 22% bracket (up to $206,700 for joint filers) and below the IRMAA threshold, resulting in an effective tax rate of 12% to 14% on conversions.
- This strategy reduces the traditional 401(k) balance to $1.5–$1.7 million by age 73, lowering the first RMD to about $60,000 and avoiding the cascade of higher taxes and Medicare surcharges.
- Retirees should front-load conversions from ages 62 to 69, then throttle back before claiming Social Security at 70 to prevent pulling benefits into taxable income.
Background
Recent data from Empower shows the average 401(k) balance is $351,242, with about one in five savers holding at least $1 million. While many Americans face retirement anxiety, those with seven-figure balances face a different challenge: managing the tax impact of large withdrawals. The 2026 landscape includes a 10-year Treasury yield of 5% and a Social Security COLA tracking near 3%, which supports strategies that delay Social Security claims and utilize low-income years for Roth conversions.
Why it matters
The decision to convert to a Roth IRA in the early 60s is a one-time, irreversible choice that can save retirees tens of thousands of dollars in taxes and Medicare premiums over their lifetime. Ignoring this window forces retirees into the highest tax terrain of their lives at age 73, where RMDs, Social Security taxation, and IRMAA surcharges compound to create an effective marginal rate approaching 40%.
What to watch
Retirees should model their first RMD by compounding their current 401(k) balance at 6% to 7% to age 73 and dividing by 26.5. If the result exceeds $80,000, they should begin partial Roth conversions that fill the 22% tax bracket but stay below the 24% threshold and the $218,000 IRMAA line. Coordination with Social Security timing is essential to maximize tax efficiency.
- A $1.5 Million 401(k) at 62 Becomes Two Very Different Retirements at 73, Depending on One Decision 24/7 Wall St.
- The RMD Mistakes That Could Increase Your Tax Bill Morningstar
- How Much Are Required Minimum Distributions for a $500,000 IRA, and When Do They Begin? Investopedia
- 5 things to know about required minimum distributions in 2026 Fast Company
- Millions Carry a Tax-Deferred Retirement 'Time Bomb' — 3 Practical Steps to Defuse It Now - Revenue Warning Signal dars.gov.et
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