Most retirees assume that Medicare premiums are fixed at enrollment, but the Social Security Administration (SSA) begins pricing coverage years before beneficiaries turn 65.
A 62-year-old with $900,000 in a traditional 401(k) has three years until enrollment and one remaining tax year outside Medicare’s premium formula.
The 2027 return directly sets the premiums charged in 2029, the year a 62-year-old today would first enroll in Medicare at age 65, according to the Centers for Medicare & Medicaid Services.
A conversion completed before this December lands on the 2026 return, which prices 2028 coverage, a full year before enrollment begins.
That timeline places the closing weeks of 2026 inside Medicare’s pricing window for a retiree weighing whether to roll over pretax 401(k) funds into a Roth account.
Missing the window could trigger a monthly premium surcharge that compounds for as long as both spouses remain enrolled in Medicare.
How Medicare’s lookback rule creates a deadline at 62
Medicare adds a surcharge called the Income-Related Monthly Adjustment Amount (IRMAA) to Part B and Part D premiums for higher-income beneficiaries.
The standard Part B premium for 2026 is $202.90 monthly, and joint filers with modified adjusted gross income (MAGI) below $218,000 owe no surcharge, the CMS confirmed.
Single filers face a lower MAGI cutoff at $109,000, and roughly 8% of Medicare beneficiaries currently pay the income-adjusted premium, CMS data showed.
The formula adds adjusted gross income from Form 1040 line 11 to tax-exempt interest from line 2a, so municipal bond income counts toward the threshold, the SSA noted.
Roth conversion proceeds, capital gains from taxable accounts, severance payments, and home-sale profits above the exclusion all flow directly into that calculation. That two-year lookback is what makes 2026 the operative year for a 62-year-old.
A conversion completed by Dec. 31, 2026, adds income tax on the transferred amount but keeps the transaction entirely outside Medicare’s premium formula for the retiree’s first coverage year.
Any conversion delayed into 2027 flows directly into that pricing calculation.
What crossing the IRMAA threshold cost a married couple
IRMAA operates on hard cliffs, so exceeding a threshold by a single dollar triggers the full surcharge for that tier.
That cliff structure catches retirees who size a Roth conversion to their federal tax bracket but overlook the IRMAA consequences two years ahead.
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Consider a married couple with combined pension income, a working spouse’s salary, and taxable investments bringing total MAGI near $210,000 in a typical year.
A $100,000 Roth conversion on top pushes joint MAGI to roughly $310,000, landing them in the second IRMAA tier under the 2026 CMS schedule.
Under the 2026 CMS schedule, that tier adds $202.90 in monthly Part B surcharges and $37.50 in Part D surcharges per person. For a couple where both spouses are enrolled, the combined annual cost is roughly $5,770.
Many retirees size Roth conversions to their current federal tax bracket without running the same calculation against Medicare’s pricing formula.
IRMAA sits outside most tax-planning software and typically surfaces only when the first premium notice arrives, long after the return that triggered it.
The threshold tightens further when one spouse dies, because the survivor shifts from the $218,000 joint filing cutoff to the $109,000 single filer cutoff, the CMS 2026 premium schedule confirmed.
Why Form SSA-44 offers no relief for voluntary conversions
Form SSA-44 lets a beneficiary appeal an IRMAA determination after a qualifying life-changing event, and the Social Security Administration limits the recognized triggers to eight categories.
The Social Security Administration recognizes eight qualifying events: marriage, divorce or annulment, death of a spouse, work stoppage, work reduction, loss of income-producing property, loss of pension income, and an employer settlement payment.
A Roth conversion is voluntary and does not qualify under any category on the form, regardless of the amount converted.
Derrick Longo, a wealth advisor at Savant Wealth Management (formerly Exencial Wealth Advisors), told Kiplinger that the IRMAA surcharge is deducted directly from monthly Social Security checks, which shrinks the cash flow many retirees depend on to cover everyday expenses.
<strong>If your Social Security is now 10% less every month, that’s a very tangible consequence</strong>.
With voluntary conversions excluded from the SSA-44 appeal path, the tax year in which a conversion occurs determines whether the income enters Medicare’s pricing formula for a retiree’s first coverage year.
How the Dec. 31 deadline decides the first Medicare premium year
Retirees born in 1960 or later do not begin required minimum distributions (RMDs) until age 75 under the SECURE 2.0 Act, the Internal Revenue Service noted.
That delay gives a 62-year-old with no wages and no Social Security benefits a window of unusually low MAGI before mandatory distributions begin.
The 24% federal bracket for joint filers spans taxable income from $211,400 to $403,550, the IRS confirmed. A conversion sized within that range on a 2026 return sits below the joint IRMAA threshold on the 2026 CMS schedule.
Taylor Schulte, CFP, founder of Define Financial, noted that even the first IRMAA tier adds roughly $2,297 per year in combined Part B and Part D surcharges for a couple where both spouses are enrolled in Medicare.
The 2026 conversion window narrows for couples approaching 65
Schulte recommended setting the conversion ceiling at the lower of the next federal tax bracket or the nearest IRMAA threshold for retirees approaching 65.
A 401(k) conversion typically requires an intermediate rollover into a traditional IRA before the funds can move into a Roth account. That extra processing step can delay the transaction past Dec. 31 if it starts late in the fourth quarter.
Once January 2027 arrives, the same conversion lands on a 2027 return that prices 2029 premiums. That turns a one-time tax bill into a recurring Medicare surcharge for every year both spouses remain enrolled.
Related: Suze Orman flags the Medicare gap retirees are missing
