The Three-Bucket 401(k) Withdrawal Hack That Can Save Retirees Six Figures in Taxes

A married couple, ages 64 and 65, retired last year with $2.4 million spread across a traditional 401(k), a Roth IRA, and a taxable brokerage account. They spend $145,000 a year. Their federal income tax bill is zero. The structure is three tax buckets emptied in the order the code effectively rewards, executed in the narrow window between retirement and Social Security at 70.

The Three-Bucket Setup

Their balances: $1.1 million in a traditional 401(k), $700,000 in a Roth IRA with the five-year clock long satisfied, and $600,000 in a taxable brokerage with a $360,000 cost basis and $240,000 of embedded long-term gains. Social Security is deferred until 70, which is the entire reason this works. No Social Security means no provisional-income calculation, no 85% inclusion trap, and full use of the standard deduction against ordinary income.

Two numbers do the heavy lifting in 2026. With both spouses 65 or older, the MFJ standard deduction lands near $32,300. The 0% long-term capital gains bracket for MFJ filers runs to roughly $96,700 of taxable income. Stack withdrawals against those two ceilings and the math falls into place.

The Withdrawal Sequence That Produces Zero

Step one: pull $32,300 from the 401(k). That hits the return as ordinary income, then the standard deduction erases it. Federal ordinary tax owed: $0. The couple is also draining the pre-tax bucket while they can do it free, shrinking the balance that will eventually drive required minimum distributions at 75.

Step two: sell $90,000 of brokerage positions. Roughly 60% of each lot is basis returning tax-free; the rest is long-term gain. Layer it on the return: $32,300 of ordinary income plus $90,000 of long-term gains equals $122,300 of gross taxable income. Subtract the $32,300 standard deduction and taxable income drops to $90,000, sitting entirely inside the 0% LTCG band. Capital gains tax owed: $0.

Step three: take $22,700 from the Roth IRA. Post-59.5 with the five-year clock cleared, every dollar is tax-free and never appears on the 1040. Add the three buckets: $32,300 plus $90,000 plus $22,700 equals $145,000. Federal tax: $0.

Why the Window Closes at 70

This sequence runs cleanly until Social Security starts. At 70, benefits land near maximum, and a chunk becomes taxable the moment provisional income crosses the threshold. The ordinary-income layer also shifts: Social Security pushes against the standard deduction, leaving less room for 401(k) withdrawals before the 0% LTCG ceiling cracks.

The bigger trap is IRMAA. The first Medicare surcharge tier for MFJ filers sits at roughly $218,000 of MAGI in 2026, and the lookback is two years. A 2026 Roth conversion shows up on 2028 Medicare premiums. With CPI at 330.3 in March 2026 and inflation sitting in the 90th percentile of historical readings, those bracket and threshold figures will keep drifting. Verify them every January at IRS.gov and CMS.gov rather than working from last year’s memory.

The Conversion Years Hidden Inside the Plan

In any year the couple defers brokerage realization, the 0% LTCG ceiling becomes empty room for Roth conversions instead. Convert traditional 401(k) dollars up to roughly $96,700 of taxable income, pay the 10% and 12% ordinary brackets on the conversion, and the tax cost is still meaningfully lower than what RMDs will trigger after 75 once Social Security is also taxable. Every dollar moved now is a dollar that will not later push MAGI through the IRMAA cliff.

What to Do This Week

1. Confirm your numbers against the 2026 IRS schedules. Pull the actual MFJ standard deduction with both spouses 65-plus and the exact 0% LTCG ceiling from IRS.gov. The figures used here are accurate for 2026 but reset annually with inflation.
2. Map your basis lot by lot. The brokerage step only works if you can identify which shares carry which cost basis. Use specific-lot identification at the broker, not average cost, so you can dial gain realization to the dollar.
3. Model the 70-year-old version of your return now. Project Social Security plus eventual RMDs against the $218,000 MFJ IRMAA threshold. If that future return crosses the line, the deferral years between 65 and 70 are your last cheap conversion runway, and every year skipped is permanent.