For most people, Obamacare after age 65 stops being a realistic option because Medicare eligibility disqualifies you from the premium tax credits and cost-sharing reductions that make marketplace plans affordable. The moment you become eligible for premium-free Medicare Part A, you lose access to ACA subsidies, even if you never actually enroll in Medicare. The one meaningful exception is people who don’t qualify for premium-free Part A, usually because they haven’t worked long enough in the U.S. paying Medicare taxes. Everyone else needs to plan a clean transition to Medicare at 65.
Why Turning 65 Ends Your ACA Subsidies
The IRS conditions premium tax credits on not being eligible for other government health coverage like Medicare.1Internal Revenue Service. Eligibility for the Premium Tax Credit HealthCare.gov states it plainly: you can’t get savings on a marketplace plan once you’re eligible for Medicare Part A.2HealthCare.gov. Changing from Marketplace to Medicare
The word doing the heavy lifting there is “eligible.” Signing up for Medicare is not the trigger. Being eligible is. If you’ve worked at least 10 years (40 quarters) paying Medicare taxes, you qualify for premium-free Part A the day you turn 65, and that eligibility alone ends your access to marketplace subsidies. You don’t have to file anything with Medicare for this to happen.
You can technically keep a marketplace plan past 65, but you’ll pay full price. And if you keep receiving premium tax credits after becoming Medicare-eligible, you’ll owe every dollar of those credits back when you file your federal taxes.2HealthCare.gov. Changing from Marketplace to Medicare For nearly everyone, that math points to Medicare.
Who Can Still Buy Subsidized Marketplace Coverage After 65
The narrow group that can keep using the ACA marketplace with subsidies after 65 is people who aren’t eligible for premium-free Part A. This mainly includes people without 40 quarters of Medicare-covered work history: immigrants who arrived in the U.S. later in life, and people whose careers were spent in jobs not covered by Social Security. If you fall into this category, you can continue buying a marketplace plan and receiving premium tax credits based on your income.1Internal Revenue Service. Eligibility for the Premium Tax Credit
For this group the choice matters, because buying into Part A is expensive. In 2026, Part A costs $311 per month with 30 to 39 quarters of work history, or $565 per month with fewer than 30 quarters.3Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles Add the standard Part B premium of $202.90 per month, and a subsidized marketplace plan can come out substantially cheaper.
One caveat for lawfully present immigrants: eligibility rules for subsidized marketplace coverage have been shifting, and some categories face changing rules in 2027. Check HealthCare.gov for the current standards before assuming you still qualify.
Ending Your Marketplace Plan When Medicare Starts
Your ACA plan does not shut off automatically when you become Medicare-eligible. You have to end it yourself through HealthCare.gov, and if you don’t, you’ll keep getting billed full price for coverage you no longer need.4HealthCare.gov. How Do I Cancel My Marketplace Plan
Since March 2025, HealthCare.gov lets you report a Medicare start date directly in the application. How you cancel depends on your household:5Centers for Medicare & Medicaid Services. When to Terminate Coverage for Consumers Transitioning from Marketplace to Medicare Coverage
- If you’re the only person on the plan, log in, open “My plans and programs,” select “End (Terminate) All Coverage,” and pick an end date. When Medicare starts on the first of a month, set the marketplace end date to the day before, so a June 1 Medicare start pairs with a May 31 marketplace end.
- If family members share the plan, log in, choose “Report a life change,” and enter your Medicare start date. The marketplace will adjust coverage so the rest of the household can keep their plan.
The clean move is to end the marketplace plan the day before Medicare begins. End it too early and you’ll have days or weeks with no coverage; end it too late and you’ll pay unsubsidized marketplace premiums on top of Medicare.
How and When to Enroll in Medicare
Your Initial Enrollment Period is seven months long: the three months before your 65th birthday, the birthday month itself, and the three months after.6Medicare.gov. When Does Medicare Coverage Start When your coverage begins depends on when in that window you sign up:
- Sign up before your birthday month and Part B starts the month you turn 65. (If your birthday is on the first of the month, coverage starts the month before.)
- Sign up during your birthday month or later and Part B starts the following month.
Premium-free Part A can be backdated up to six months, so hospital coverage can reach back even if you enroll late in the window. Part B cannot be backdated, which is why timing matters if you need outpatient care covered right away.
People already receiving Social Security benefits at least four months before turning 65 are enrolled in Parts A and B automatically, with the Medicare card arriving about three months before the birthday.7Medicare.gov. How Do I Sign Up for Medicare Everyone else has to apply through the Social Security Administration online at ssa.gov or by calling 800-772-1213.8Social Security Administration. Plan for Medicare – Sign Up for Medicare
What Happens If You Miss the Window
Missing the Initial Enrollment Period for Part B triggers a lifetime penalty. The surcharge adds 10% to your Part B premium for each full 12-month period you could have signed up but didn’t. Delay two years and you’ll pay 20% extra on top of the $202.90 standard premium — roughly $243.50 per month in 2026, permanently.9Medicare.gov. Avoid Late Enrollment Penalties
If you miss the Initial Enrollment Period entirely, the next opportunity is the General Enrollment Period, January 1 through March 31 each year. Coverage doesn’t begin until the month after you enroll, and the late enrollment penalty still applies.10Social Security Administration. When to Sign Up for Medicare
If You’re Still Working at 65
You can delay Part B without a penalty if you or your spouse are still working and covered by an employer health plan.11Medicare.gov. Working Past 65 Employer size changes how this works:
When the employer has 20 or more employees, the employer plan pays first and Medicare would be secondary, so delaying Part B is safe. When the employer has fewer than 20 employees, Medicare is the primary payer and the employer plan is secondary. Delaying Part B in that situation leaves you without primary coverage and triggers the late enrollment penalty.12Centers for Medicare & Medicaid Services. MSP Employer Size Guidelines for GHP Arrangements – Part 1
Once employment or employer coverage ends, an eight-month Special Enrollment Period opens for Part B signup with no penalty.13Social Security Administration. How to Apply for Medicare Part B During Your Special Enrollment Period The clock starts when the job or coverage ends, whichever comes first. Part B coverage during a Special Enrollment Period begins the month after you sign up, so waiting until the end of the eight months creates a gap.
One thing that trips people up: even while you’re delaying Part B because of employer coverage, you still can’t get ACA marketplace subsidies. Either employer coverage or eligibility for premium-free Part A disqualifies you from premium tax credits.2HealthCare.gov. Changing from Marketplace to Medicare
COBRA Is Not Employer Coverage for This Purpose
COBRA continuation coverage does not count as coverage based on current employment for Medicare’s rules.14Medicare.gov. COBRA Coverage If you retire at 65 and elect COBRA, your eight-month Special Enrollment Period for Part B runs from the date you stopped working, not from the date COBRA ends. Someone who leans on COBRA for 18 months after retirement and then tries to sign up for Part B will discover the Special Enrollment Period ended 10 months earlier, along with a permanent penalty. Retiree health plans and VA coverage don’t count as current employment coverage either.
The HSA Trap at Age 65
If you’ve been contributing to a Health Savings Account through a high-deductible health plan, Medicare enrollment ends that. Starting with the first month you’re enrolled in Medicare, your HSA contribution limit is zero.15Internal Revenue Service. Publication 969, Health Savings Accounts and Other Tax-Favored Health Plans
The retroactive coverage rule creates the real problem. When you apply for Part A after 65, Medicare can backdate coverage up to six months (though not before your 65th birthday). Any HSA contributions you or your employer made during those retroactive months become excess contributions, subject to a 6% excise tax each year they remain uncorrected. You can reverse the overcontribution by contacting your HSA administrator before you file your tax return for that year, and if HSA funds were invested you also need to withdraw the associated earnings.
The safe move: if you plan to delay Medicare past 65 to keep contributing to an HSA, stop contributions at least six months before you intend to enroll. For 2026 the maximum HSA contribution is $4,400 for self-only coverage and $8,750 for family coverage, so the exposure isn’t trivial.15Internal Revenue Service. Publication 969, Health Savings Accounts and Other Tax-Favored Health Plans Spending existing HSA funds on qualified medical expenses after Medicare enrollment is fine. The restriction only applies to new contributions.