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 relief 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. Medicare had added $487 a month to her Part B premium, traced straight back to that satisfying payoff.

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

Why a Debt-Free Move Triggered a Medicare Bill

Medicare looks backward. The 2026 Part B premium is based on the income reported on the 2024 tax return. That two-year lookback is the trap. A traditional 401(k) withdrawal counts as fully taxable ordinary income, so a lump sum big enough to retire a mortgage often lands in a single year and pushes Modified Adjusted Gross Income (MAGI) into territory the retiree never normally occupies.

IRMAA is also a cliff. One dollar over a threshold triggers the entire tier. The standard 2026 Part B premium is $202.90 a month. At the top tier, which kicks in at MAGI of $500,000 or more for a single filer or $750,000 for a joint return, the surcharge adds $487 per month on top of that base. 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 top bracket for one strange year.

Because Medicare premiums are pulled directly from the Social Security check, the hit shows up as a smaller deposit rather than a separate bill. That is what makes the surprise sting.

The One Detail That Drives the Whole Outcome

The single most important variable 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 a threshold the retiree would otherwise never approach. Split across late December and early January, the same payoff hits two separate tax years, and each year’s MAGI may stay safely below the next IRMAA cliff. Same house, same lender, same total dollars paid. Wildly different Medicare bill.

Roth withdrawals offer another lever, because qualified Roth distributions do not count toward MAGI. Neither does drawing on principal from a regular taxable brokerage account. A blended payoff, including some Roth, some taxable savings, some traditional spread over two years, often clears the mortgage without brushing a surcharge tier.

How This Lands Alongside the Rest of Retirement

Once the surcharge is in place, the calendar becomes the relief valve. IRMAA is recalculated every year, so when 2025 income returns to normal, the 2027 premium should drop back to the standard amount. The damage is real but usually temporary, often lasting a single year.

Appealing is the part people get wrong. The Social Security Administration’s SSA-44 form covers specific life-changing events such as retirement, the death of a spouse, or a divorce. Choosing to pay off a mortgage is not on that list. The fix happens before the withdrawal, not after.

What to Think Through Before Pulling the Trigger

The good news is that every lever here is available before the withdrawal, not after.

1. Before any large traditional 401(k) withdrawal, run the MAGI math against the IRMAA thresholds. A payoff that saves a few thousand in mortgage interest but triggers a five-figure tax bill and a Medicare surcharge 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.