When one person in a household enrolls in Medicare, that person loses eligibility for the Affordable Care Act premium tax credit, and the subsidy for anyone remaining on a Marketplace plan is recalculated, usually downward. That is the short version of what happens to the ACA subsidy when one spouse goes on Medicare. The longer version matters in 2026, because the 400% federal poverty level income cliff is back and excess advance credits now have to be repaid in full with no caps.
Why the Medicare-Eligible Person Loses the Subsidy
Premium tax credits are only available to people who aren’t eligible for other qualifying coverage, and Medicare counts. Once you qualify for premium-free Part A, you can no longer receive a subsidy on a Marketplace plan, even if you haven’t actually enrolled in Medicare yet. Eligibility by itself is disqualifying.1Internal Revenue Service. Eligibility for the Premium Tax Credit
If the Medicare-eligible person keeps a Marketplace plan anyway, they pay the full unsubsidized premium. Any advance premium tax credits they receive after becoming Medicare-eligible have to be paid back at tax time.2HealthCare.gov. Changing from Marketplace to Medicare
The Narrow Exception
Premium-free Part A requires at least 40 quarters of work credits, roughly 10 years of paying Medicare taxes. If you don’t meet that threshold, Part A comes with a monthly premium, and in that situation you actually have a choice: you can compare the full cost of Medicare against your subsidized Marketplace plan and pick whichever works out better financially.2HealthCare.gov. Changing from Marketplace to Medicare Most people qualify for premium-free Part A, so this exception is narrow.
How the Remaining Spouse’s Subsidy Gets Recalculated
Two things change at once, and both usually work against the spouse who stays on the Marketplace plan.
The benchmark premium drops. Your subsidy is calculated against the second-lowest-cost silver plan for the people actually enrolling. With one fewer person, that benchmark shrinks. Since the subsidy equals the benchmark minus your expected contribution, a smaller benchmark means a smaller credit.
Household income, meanwhile, doesn’t shrink. The Marketplace uses modified adjusted gross income for the whole tax household, including the spouse who moved to Medicare. On a joint return, that spouse’s income still counts in full.3HealthCare.gov. What’s Included as Income So the calculation runs on the same income against a lower benchmark, and the credit for the remaining spouse gets noticeably smaller.
Social Security Often Makes It Worse
Turning 65 frequently coincides with starting Social Security, and Social Security benefits count in MAGI for Marketplace purposes, both taxable and non-taxable portions.3HealthCare.gov. What’s Included as Income A household that was comfortably subsidy-eligible can suddenly find itself with a higher expected contribution, a smaller credit, or no credit at all. This is the piece that catches households by surprise: one spouse moves to Medicare, starts collecting benefits, and the other spouse’s Marketplace subsidy drops far more than the loss of one enrollee would suggest.
The 2026 Income Cliff at 400% of the Federal Poverty Level
From 2021 through 2025, expanded premium tax credits removed the upper income limit, and households above 400% FPL could still qualify. That expansion expired at the end of 2025.4HealthCare.gov. Premium Tax Credit – Glossary
For 2026, the cliff is back. Household MAGI above 400% FPL means zero premium tax credit. For a two-person tax household, the cutoff is $86,560; for a single filer, $63,840.5Federal Register. Annual Update of the HHS Poverty Guidelines Because the remaining spouse’s income still includes the Medicare spouse’s earnings and Social Security, it takes very little extra income to push a household over the line and lose the subsidy entirely.
What You Have to Do, and When
Marketplace coverage does not end automatically when Medicare starts. You have to log in and update your Marketplace application to end coverage for the person going on Medicare. If you don’t, you keep paying Marketplace premiums and, worse, keep collecting advance subsidy payments you’re no longer entitled to.6HealthCare.gov. Learn What to Do if You Already Have Medicare Health Coverage
You can report the Medicare start date up to three months in advance. If Medicare begins May 1, you can update the application as early as February 1, and Marketplace coverage for that person will end April 30, the day before Medicare kicks in.2HealthCare.gov. Changing from Marketplace to Medicare There is no fixed reporting deadline, but CMS says to report life changes as soon as they happen, and the sooner you report, the sooner the Marketplace adjusts advance credits for the remaining spouse.7Centers for Medicare & Medicaid Services. Report Life Changes When You Have Marketplace Coverage
Once you report the change, the remaining household members generally get a Special Enrollment Period: 60 days from the qualifying event to enroll in a new plan or switch coverage.8HealthCare.gov. Special Enrollment Opportunities Use that window to reprice options based on the new, smaller subsidy. A different plan or metal tier may make more sense for one person than it did for two.
The 2026 Repayment Rule Makes Delay Expensive
If your household receives more in advance premium tax credits during the year than it turns out to qualify for, the excess is repaid at tax time on Form 8962.9Internal Revenue Service. Premium Tax Credit – Claiming the Credit and Reconciling Advance Credit Payments
Through 2025, households below 400% FPL had dollar caps on that repayment. A single filer under 200% FPL, for example, would repay no more than $375. Those caps are gone. Section 71305 of Public Law 119-21 eliminated all repayment limitations starting with tax year 2026, so every dollar of excess advance credit must be repaid in full, at every income level.10Medicaid.gov. Federal Funding Methodology for Program Year 2026
That is why the Medicare transition is more financially dangerous in 2026 than it used to be. If the Medicare-eligible spouse stays on the Marketplace application for months after becoming eligible, or if the remaining spouse’s recalculated subsidy is smaller than the advance payments already flowing, the family collects credits it isn’t entitled to and owes the full amount back at tax time. Reporting the change promptly is the single most useful thing you can do to keep that bill from growing.
Two Deadlines the Same Transition Triggers
The subsidy question isn’t the only clock running when a household member ages into Medicare. Skipping Part B when first eligible, without creditable employer coverage, triggers a late enrollment penalty of 10% added to the monthly Part B premium for each full 12-month period of delay, and that penalty lasts for as long as you have Part B. A Marketplace plan does not count as creditable coverage for this purpose.11Medicare. Avoid Late Enrollment Penalties
Enrolling in Part B at 65 or older also opens a one-time, six-month Medigap Open Enrollment Period. During that window, insurers must sell you any Medigap policy available in your state regardless of health history. Once it closes, they can refuse coverage or charge more based on your health, outside of limited guaranteed-issue situations.12Medicare. Buying a Medigap Policy Both of these run on the Medicare side of the transition, but they’re easy to miss when the household is focused on the Marketplace side.