Every Year a Retired Couple Leaves the $47,500 Tax-Free Space Empty, About $5,700 of Tax Moves Into Their 70s. Most Leave It Empty for Ten Years

It’s important to examine Roth conversion planning during the low-income window between retirement and the start of required withdrawals. This is especially true when a couple leaves the low-bracket space empty and effectively makes a scheduling decision. The schedule they choose sends the tax bill to the decade when their income is highest, and their flexibility is lowest. The $47,500 of tax-free space that goes unused each year quietly moves the liability into a later decade. When it does, about $5,700 of tax relocates into the couple’s 70s. In many households, that happens for something like a decade before anyone notices.

Compounding in the 70s

The pre-tax balance keeps growing across the empty years, so the mandatory withdrawal that eventually arrives is calculated against a larger number. By the time it starts, Social Security is usually running, and the withdrawal stacks on top of benefits. The 2027 Social Security COLA is tracking toward 3.1%, raising the base every year the withdrawal sits on top of it.

The withdrawal itself is required, and the timing is set by rule. A retiree who would prefer to take less in a weak market year cannot. The withdrawal then pushes more of the Social Security benefit into the taxable column, so one forced event creates a second tax consequence on the same return. Some of these households also trip the income-related Medicare Part B surcharge, which is assessed on income from two years earlier. The premium increase lands in a later year, with the standard Part B premium at $202.90 in 2026 and surcharge tiers that can push the total meaningfully higher. The surcharge often isn’t tied to a conversion decision made years earlier.

How the Window Closes Quietly

Nothing announces the end of the low-income years. There is no form that arrives to tell you something is happening. The couple simply claims Social Security, or reaches the age at which withdrawals become mandatory, and the cheap years are behind them. The window is bounded on both ends. It opens when earned income stops and closes when benefits or forced withdrawals begin. Delaying Social Security lengthens it, which is one argument for waiting to claim.

Why Most Couples Leave It Empty

Voluntarily creating a tax bill feels irrational when no one is forcing one. It goes without saying that paying tax you didn’t have to pay this year is emotionally hard, even when it is the right move. Retirement-year spending anxiety tends to protect cash, and the conversion tax has to come from somewhere. The $78,535 average annual expenditure figure reported by the 2024 Consumer Expenditure Survey is a reasonable proxy for how committed a household’s cash flow already is, and any conversion tax competes with that.

Nobody sends a notice, either, and no annual statement shows unused deduction space. Advisers compensated on assets under management have little incentive to raise the subject, and couples without an adviser have none. The behavior is common across households without an adviser prompting the conversation.

Building an Annual Routine

Treating the conversion as an annual exercise, sized to the space available each year, fits how the window actually works. Room changes with income and with law, so the amount worth converting changes too. Converting early in the year requires a plan to cover the tax through estimated payments or withholding, because the obligation arrives during the year rather than at filing. That timing catches people, and it is worth understanding before you initiate the first conversion.

The conversion decision belongs in the same conversation as the Social Security claiming decision, because the two interact directly. Revisiting the plan annually matters because the deduction that creates much of this space has an income phase-out and is not permanent under current law. Doing the exercise with someone who models the full return, including how a conversion changes the taxability of benefits and any Medicare surcharge two years out, is usually the difference between a routine that works and one that backfires (we sized up that quiet stretch between the last paycheck and the first required withdrawal in a free guide here: The Roth Window). Kiplinger’s recent coverage of how soft retirement changes 2026 Roth conversion strategy makes the same point: the low-income window can be narrow and variable.

A Decade of Decisions Made by Default

The tax is owed in either case; the variable is which decade it lands in and whether the couple sets the timing. Leaving the window empty for a decade shifts that timing to years when rates and required withdrawals are outside the couple’s control. This is an illustration and not personalized advice.

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