A 67-Year-Old Cashed Out Her 401(k) to Wipe Out the Mortgage, Then Medicare Added $487 a Month Two Years Later

The moment she signed the check that cleared her mortgage, a 67-year-old retiree felt the quiet relief that only a debt-free homeowner knows. She had pulled a single large lump sum from her traditional 401(k), wired it to the lender, and finally owned the house outright. Two years later, her Social Security deposit shrank without warning. Medicare had tacked on $487 a month to her Part B premium, and the cause traced straight back to that satisfying payoff.

This scenario is more common than most retirees realize. Versions of this story surface regularly on retirement forums: someone clears the mortgage with one large withdrawal, then opens a letter from Social Security a couple of years later and wonders what happened. The culprit carries a clunky name, the Income-Related Monthly Adjustment Amount, or IRMAA, and it catches careful, responsible savers more reliably than almost anyone else.

Why a Debt-Free Move Triggered a Medicare Bill

Medicare looks backward. The 2026 Part B premium is based on income reported on the 2024 tax return, and that two-year lookback is exactly where the trap lives. A traditional 401(k) withdrawal is fully taxable ordinary income. A lump sum large enough to retire a mortgage lands on a single tax return and can push Modified Adjusted Gross Income (MAGI) into territory the retiree would otherwise never approach.

One detail surprises many people. MAGI for IRMAA purposes includes not just wages, pensions, and retirement distributions, but also tax-exempt interest from municipal bonds. A retiree who holds a substantial muni portfolio for its tax advantages may still find that interest pushing a surcharge tier.

IRMAA operates as a pure cliff system. One dollar over a threshold triggers the full tier surcharge, with no prorated middle ground. The standard 2026 Part B premium is $202.90 a month, up from $185.00 in 2025. Surcharges begin once MAGI crosses $109,000 for a single filer or $218,000 for a joint return, with the Part B add-on ranging from $81.20 at the first tier to $487.00 at the top. That top tier starts at $500,000 for a single filer or $750,000 for a joint return. It is currently frozen and will not be indexed for inflation until Congress acts. Stack a six-figure 401(k) withdrawal on existing Social Security, pension, and investment income, and a retiree who normally lives modestly can land in the highest bracket for one unusual year.

IRMAA also applies to Part D drug coverage, where the top-tier surcharge adds another $91.00 a month. Combined, a single beneficiary at the top tier faces $578 a month in income-related surcharges across Part B and Part D before accounting for the standard premiums. About 5.1 million Medicare beneficiaries paid Part B IRMAA surcharges in 2025, roughly 7% of all enrollees. That figure illustrates how many otherwise moderate-income retirees a single large distribution can sweep into surcharge territory for one year.

Because Medicare premiums are deducted directly from the Social Security check, the hit arrives as a smaller deposit rather than a separate bill. That quiet subtraction is what makes the surprise sting so much.

The One Detail That Drives the Whole Outcome

The single most important variable in this situation is not the size of the mortgage or the interest rate. It is whether the payoff happens in one tax year or two.

Picture a $300,000 mortgage balance. Pulled from a traditional 401(k) in one calendar year, the full amount lands on a single tax return and can rocket MAGI past surcharge thresholds the retiree would otherwise never approach. Split across late December and early January, the same payoff hits two separate returns, and each year’s MAGI may stay safely below the next IRMAA cliff. Same house, same lender, same total dollars. Wildly different Medicare bill.

Roth withdrawals offer another lever. Qualified Roth distributions do not count toward MAGI, so drawing from a Roth account adds nothing to the IRMAA calculation. Drawing principal from a regular taxable brokerage account also avoids adding to MAGI beyond any realized gains. A blended payoff, combining some Roth, some taxable savings, and some traditional funds spread across two years, can often clear the mortgage without brushing a surcharge tier.

One development worth flagging for 2025 filers: the One Big Beautiful Bill Act, signed into law on July 4, 2025, created a new $6,000 bonus deduction for each taxpayer age 65 and older, temporary through 2028. Qualifying married couples where both spouses are 65 or older and both carry valid Social Security numbers can claim up to $12,000. The deduction phases out for single filers with MAGI above $75,000 and is fully eliminated at $175,000. For joint filers, the phase-out begins at $150,000 and disappears entirely at $250,000. Critically, this is a below-the-line deduction. It reduces taxable income but not MAGI itself. Because IRMAA is calculated against MAGI, a retiree hoping the new write-off will pull them under a surcharge threshold will be disappointed. The Medicare calculation is unaffected, regardless of whether a senior qualifies for the full deduction, a reduced amount, or nothing at all.

How This Lands Alongside the Rest of Retirement

Once a surcharge is in place, the calendar is the primary relief valve. IRMAA is recalculated every year using the most recent available tax return. When income returns to its normal level, the following year’s premium drops back to the standard amount. The financial hit is real, but it is typically temporary, confined to a single year tied to that one outsized withdrawal.

Appealing is the part people consistently get wrong. The Social Security Administration’s SSA-44 form covers eight specific life-changing 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 related to employer bankruptcy or reorganization. Choosing to pay off a mortgage is not on that list. A voluntary lump-sum retirement withdrawal has no qualifying appeal path under SSA-44, which means the fix has to happen before the withdrawal, not after.

What to Think Through Before Pulling the Trigger

Every lever available in this situation works before the withdrawal. None of them work once the check has cleared.

1. Before any large traditional 401(k) withdrawal, run the MAGI math against the IRMAA thresholds for both Part B and Part D. A payoff that saves a few thousand dollars in mortgage interest but triggers a five-figure tax bill and a year of Medicare surcharges is not the win it looks like on paper.
2. If the goal is to be debt-free, spread the withdrawal across two tax years, or blend in Roth and taxable-account dollars. The mortgage still goes away. The surcharge does not have to come with it.

Every retiree’s tax picture is a little different, and the line between a clean payoff and an expensive one can come down to which December week the check is signed. A short conversation with a tax preparer before the withdrawal almost always pays for itself many times over.

Editor’s note: This pass added the clarification that the One Big Beautiful Bill Act senior deduction expires after 2028 and requires both spouses to carry valid Social Security numbers for the full $12,000 joint deduction, and confirmed the 5.1 million Medicare beneficiaries figure against the Medicare Trustees Report.

Contact [email protected] for any questions or corrections.