The 62-to-70 Window: Why This Is Your Most Valuable 401(k) Tax Opportunity

A retired couple, both 62, walked into the year with $1.6 million in a traditional 401(k), $750,000 in a Roth IRA, and $650,000 in a taxable brokerage with a $400,000 cost basis. Three million dollars on the nose. They want to spend $160,000 a year and delay Social Security to age 70. The question: how do you fund the next eight years of living expenses while pushing federal income tax close to zero and shrinking the future RMD base?

The answer is a bracket-stacking sequence that uses the gap between retirement and Social Security as a tax-planning runway. Done right, it produces a decade of single-digit effective federal rates on a high-six-figure lifestyle.

Why the 62-to-70 Window Is the Most Valuable Tax Asset They Own

With no wages, no Social Security, and no RMDs yet, this couple controls almost every line on their 1040. That control disappears when Social Security starts and again at age 73 when RMDs begin. Every dollar left inside the traditional 401(k) at that point becomes ordinary income on a schedule the IRS dictates, often stacked on top of taxable Social Security and triggering IRMAA Medicare surcharges.

The mechanic that changes everything is the interaction between two separate brackets that both reset each year: the ordinary-income bracket the standard deduction shelters, and the 0% long-term capital gains bracket that sits underneath the 15% LTCG rate.

The Year-One Math, Line by Line

Here is what their first year looks like:

1. Roth conversion to fill the 12% bracket. They move $66,950 from the traditional 401(k) into the Roth IRA. Combined with the roughly $30,000 MFJ standard deduction, that conversion lands entirely inside the 10% and 12% ordinary brackets. Federal tax on the conversion: about $7,700 blended.
2. Harvesting gains at 0%. They sell $93,750 of brokerage holdings, with $56,250 of basis and $37,500 of long-term gain. Because the 0% LTCG bracket for married filers extends to roughly $96,700 of taxable income, that $37,500 gain stacks on top of the conversion and still falls inside the zero-rate zone. Federal tax on the gain: zero.
3. Funding the $160,000 lifestyle. The $93,750 brokerage proceeds plus Roth contribution basis cover the spending need. Tax on the actual cash that hits the checking account: $0. The only check written to the IRS is the conversion tax, and that tax buys tax-free growth forever.

Total taxable income on the return: $66,950 of ordinary plus $37,500 of LTCG, less the $30,000 deduction, or $74,450. Effective federal rate on $160,000 of lifestyle spending: low single digits.

Repeat Until Age 73, Then Watch the RMD Shrink

Run that sequence eight or nine more times and the traditional 401(k) is largely drained into the Roth before the first RMD year. The remaining traditional balance at 73 is small enough that the required distribution lands inside the standard deduction rather than punching through into taxable Social Security or IRMAA tiers. The Roth compounds untouched and represents the longest tax-free runway the couple owns.

Two pressure points matter. First, IRMAA uses a two-year lookback at age 65, so the most aggressive conversion years should land at 62 and early 63 to keep modified AGI off the Medicare surcharge radar when enrollment hits. Second, inflation is doing real work against a fixed budget: CPI sits at 330.3, in the 90th percentile of its 12-month range, and core PCE has climbed from about 126 a year ago to roughly 129 recently. The $160,000 budget needs to escalate, which means the conversion ladder should escalate with it.

What to Do This Quarter

1. Pin down the 2026 brackets before converting. Verify the current MFJ standard deduction, the top of the 12% ordinary bracket, and the 0% LTCG ceiling against IRS published figures. The strategy collapses if the conversion overshoots by even a few thousand dollars and pushes gain into the 15% rate.
2. Front-load conversions in 2026 and 2027. Finish the bracket-stacked conversions before the second half of age 63 so the IRMAA two-year lookback at 65 sees clean MAGI. After that, throttle conversions to whatever stays under the first IRMAA tier.
3. Park the cash reserve in T-bills. 52-week Treasury bills yield 3.75% and 13-week bills yield 3.69%, which is meaningful carry on the one to two years of spending money sitting outside the market during the conversion window.

Three million dollars sequenced through eight zero-tax years builds a comfortable retirement.