She Retired at 64 With $380,000 in a 401(k) and No Income for Nine Years. She Never Converted a Dollar. Her First RMD Was Taxed at 22%.

Conversion Capacity Does Not Carry Forward

Every year she did not convert, that 12% bracket space expired forever. Meanwhile, her untouched $380,000 balance compounded. At an average 6% annual return over those nine years, the account swelled to roughly $642,000 by age 73. When her required beginning date arrived, the IRS Uniform Lifetime Table (divisor of 26.5) mandated a first-year RMD of about $24,200. Stacked on top of the maximum Social Security benefit she began collecting at 70 (where 85% is taxable), that mandatory distribution pushed her taxable income past the 12% ceiling ($50,400), ensuring the top dollars of her first RMD were taxed at 22%.

What a Conversion Plan Would Have Done

The standard playbook for someone in her position is annual partial Roth conversions sized to the top of a chosen bracket. A conversion moves money from a traditional 401(k) or IRA into a Roth, triggers ordinary income tax on the converted amount, and then lets that money grow and be withdrawn tax-free. Filling the 12% bracket each year for nine years would have shifted a large share of the pre-tax balance into a Roth at 12%, permanently reducing the balance that RMDs are later calculated on (those low-tax years between the last paycheck and the first RMD are the whole subject of our free Roth Window guide). Two operational details matter. Pay the tax on each conversion from taxable savings rather than from the converted amount, so the full converted dollar keeps compounding inside the Roth. And conversions should be coordinated with the Social Security claiming decision, because once Social Security begins, more of every conversion dollar gets taxed, and more of the Social Security itself becomes taxable.

Broader Context

The 10-year Treasury yield was 4.67% on August 27, 2026, and the 2027 Social Security COLA is tracking toward 3.1%. Both figures matter because a retiree relying on Social Security plus mandatory withdrawals will see the taxable share of income rise mechanically as balances compound and benefits adjust.

What the Case Actually Shows

The nine-year window was the cheapest tax environment she would ever occupy. Leaving it untouched concentrated the tax bill into the years when she had the least flexibility, on a balance that had grown at a rate set by the interaction of RMDs and Social Security rather than by anything she chose.

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