She Kept Her Obamacare Plan and Its Subsidy Past 65. The IRS Took the Subsidy Back at Tax Time, and Medicare Added a Penalty for Life.
Turning 65 triggered Medicare automatically, but two separate systems kept sending money as if nothing had changed, and neither one warned her that a five-figure tax bill and a permanent monthly penalty were quietly taking shape.
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She turned 65 in March while already collecting Social Security. Medicare automatically enrolled her in premium-free Part A and Part B, but she declined Part B because her HealthCare.gov plan worked well and the subsidy covered most of its premium. The Marketplace plan did not cancel itself when Medicare began. Neither did the advance premium tax credit flowing to the insurer every month.
At the next tax season, Form 8962 exposed the overlap. Her income left the repayment uncapped, and ten months of $900 advance credits produced a bill approaching $9,000. By the time she finally enrolled in Part B, two full 12-month periods had passed. Medicare added a permanent 20% penalty. Two systems had kept paying exactly as instructed. She was the one left to reconcile them.
How Medicare Ends the Subsidy
Premium-free Medicare Part A is government-sponsored minimum essential coverage. Once Part A begins, or the tax rules treat someone as eligible for it, the premium tax credit for Marketplace insurance generally ends. For someone already collecting Social Security, the transition can happen automatically because Part A usually begins at 65. The Marketplace, however, does not automatically terminate the plan or subsidy. The beneficiary must update the Marketplace application.
At tax time, Form 8962 compares the advance premium tax credit paid to the insurer with the credit the taxpayer was actually allowed. Any excess becomes additional tax, although income-based repayment limits may reduce the amount for some households. Not collecting Social Security delays the automatic handoff. It does not keep the Marketplace subsidy alive indefinitely.
When a Medicare application is required, tax rules generally give the person through the third full calendar month after becoming eligible to complete it. Miss that deadline, and the person can be treated as eligible for premium-free Part A even without enrolling. The Marketplace policy may continue, but generally at full price.
Why Part B Keeps Its Own Clock
The tax return settles the subsidy mistake. Avoiding the Part B penalty is harder. Medicare’s standard Special Enrollment Period (SEP) applies to people who delayed enrollment while covered by an employer group plan based on their own or a spouse’s current work. A Marketplace policy is individual coverage, so it does not qualify. Without that protection, two consequences can follow once the seven-month Initial Enrollment Period closes:
- A wait for the General Enrollment Period, which runs from January through March, with coverage generally beginning the following month
- A penalty equal to 10% of the standard Part B premium for every full 12-month period the person could have enrolled but did not
In most cases, the penalty lasts as long as the person has Part B. Limited relief may exist when a government agency, employer or health plan supplied misinformation, but simply preferring Marketplace coverage does not erase the delay.
What Two Years Late Costs
The standard Part B premium is $202.90 a month in 2026. A 20% penalty adds $40.58 monthly, or approximately $487 a year. At today’s premium, that approaches $4,900 over 10 years. The actual cost will probably be higher because the penalty is recalculated as the standard premium changes. The subsidy repayment is the bill she sees first. The Part B penalty is the one that keeps returning. IRMAA surcharges and other premium traps compound the damage for higher-income retirees, which is why we mapped the full set in a free Medicare guide here.
The Birthday Is the Handoff
Three steps can keep the transition clean:
- If Social Security is already arriving, check the Medicare card for the Part A and Part B effective dates instead of waiting for a separate enrollment reminder.
- Enroll in Part B during the Initial Enrollment Period unless current-employment group coverage creates a valid reason to delay.
- End the Marketplace subsidy when Medicare eligibility begins. Coverage for other household members can remain in place after the application is updated.
If an overlap has already occurred, complete Form 8962 with the correct Medicare dates and check whether an income-based repayment limit or retroactive-coverage rule changes the amount owed. Marketplace coverage and Medicare are not interchangeable lanes past 65. Make the handoff deliberately, and the birthday becomes a clean change in coverage instead of the start of two penalty clocks.
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Gerelyn Terzo is the author of dividend investing handbook "Dividend Investing Strategies: How to Have Your Cake & Eat It Too." A veteran financial journalist, she covers agri-finance for outlets like Global AgInvesting and the broader stock market and personal finance for 24/7 Wall Street. She began at CNBC and later helped launch Fox Business in New York. Gerelyn currently resides in Woodland Park, Colorado and dabbles in nature photography as a hobby.
