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William Gray
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ACA to Medicare Transition
Switching from Marketplace Insurance to Medicare at 65
When you turn 65, your ACA Marketplace plan and its premium subsidies end. Understanding the exact timing — and acting during your Medigap Open Enrollment Period — can protect your coverage options for life.
No cost · No obligation · Independent guidance
Educational content only. This page is for educational purposes only. Coverage rules, subsidy eligibility, and enrollment periods depend on your specific situation. Consult a licensed professional before making Medicare coverage decisions.
Your ACA subsidies end when Medicare begins
If you receive a premium tax credit (APTC) through the ACA Marketplace, that subsidy ends the month you become eligible for Medicare Part A — typically the month you turn 65. You are no longer eligible for premium tax credits once you are entitled to Medicare, even if you have not yet enrolled.
This means your Marketplace plan premium could increase substantially the month your Medicare eligibility begins. Many people are surprised to learn that simply delaying Medicare enrollment does not preserve subsidy eligibility — the subsidy ends based on Medicare entitlement, not enrollment.
If you continue your Marketplace plan after becoming Medicare-eligible, you will pay the full unsubsidized premium. For most people, enrolling in Medicare Parts A and B on time is the financially sound choice.
Your Initial Enrollment Period: the 7-month window
Your Initial Enrollment Period (IEP) for Medicare is a 7-month window: the 3 months before your 65th birthday month, your birthday month itself, and the 3 months after. Enrolling in Part B during the first 3 months of your IEP means your coverage starts the month you turn 65.
If you enroll during your birthday month or the 3 months after, your Part B coverage is delayed by 1 to 3 months. This delay matters because your Medigap Open Enrollment Period is tied to when your Part B coverage begins — not to your birthday.
Missing your IEP without a qualifying Special Enrollment Period can result in a permanent Part B late enrollment penalty of 10% per 12-month period you were eligible but not enrolled.
Your Medigap Open Enrollment Period: the most important window
Your Medigap Open Enrollment Period (OEP) is a 6-month window that begins the first month you are both age 65 or older AND enrolled in Medicare Part B. During this window, you have a federal guaranteed-issue right to purchase any Medigap plan sold in your state — no medical underwriting, no health questions, no denial.
This is the single most important enrollment window for people transitioning from Marketplace coverage to Medicare. Once your Medigap OEP closes, applying for a Medigap plan in most states requires passing medical underwriting. Pre-existing conditions can result in higher premiums or denial.
The Medigap OEP is not the same as the Medicare Annual Enrollment Period (AEP). AEP runs October 15 through December 7 each year and applies to Medicare Advantage and Part D plans — it does not create a new Medigap OEP or guaranteed-issue right for most people.
To protect your Medigap OEP, enroll in Part B as early as possible during your IEP. Delaying Part B enrollment delays the start of your Medigap OEP.
Want to understand your Medigap OEP in detail?
Read the complete Medigap guaranteed-issue rights guidePart D: enroll when you enroll in Part B
Your ACA Marketplace plan likely included prescription drug coverage. Medicare does not automatically include drug coverage — you must enroll in a standalone Part D plan or a Medicare Advantage plan that includes drug coverage (MAPD).
If you choose Original Medicare with a Medigap supplement, you will need a separate Part D plan. Your IEP for Part D runs concurrently with your IEP for Part B. Enrolling late without creditable drug coverage results in a permanent Part D late enrollment penalty.
The 2027 Part D annual deductible is $700, and the out-of-pocket cap is $2,400. Specific plan premiums and formularies vary by carrier and ZIP code.
Your transition checklist
Confirm your Medicare eligibility date
Most people become eligible for Medicare the first day of their birthday month. If your birthday is the first of the month, eligibility begins the first day of the prior month.
Enroll in Part A and Part B during your IEP
Sign up through Social Security (ssa.gov) or your local Social Security office. Enroll in the first 3 months of your IEP to start coverage on your 65th birthday.
Shop Medigap plans before Part B starts
Contact an independent broker before your Part B effective date. Your Medigap OEP begins the first month you have both Part B and are age 65+. Shopping early gives you time to compare carriers and premiums.
Enroll in a Part D plan
Choose a standalone Part D plan that covers your prescriptions. Compare formularies and premiums at Medicare.gov/plan-compare.
Cancel your Marketplace plan
Once your Medicare coverage begins, notify your Marketplace plan to cancel. You may be eligible for a Special Enrollment Period to cancel outside the normal window when you gain Medicare coverage.
Verify subsidy repayment obligations
If you received APTC for months after your Medicare entitlement began, you may owe repayment at tax time. Consult a tax professional if you are uncertain.
Not sure when to enroll or which plan to choose?
William Gray is an independent Medicare broker who can walk you through your exact transition timeline — at no cost to you.
Frequently asked questions
Can I keep my ACA Marketplace plan after turning 65?
Yes, you can keep your Marketplace plan, but you will lose your premium tax credit subsidy the month you become eligible for Medicare. You would pay the full unsubsidized premium. For most people, enrolling in Medicare is the more cost-effective choice.
What happens to my ACA subsidy when I turn 65?
Your premium tax credit (APTC) ends the month you become entitled to Medicare Part A, which is typically the month you turn 65. Entitlement is based on eligibility, not enrollment — you lose the subsidy even if you have not yet enrolled in Medicare.
When does my Medigap Open Enrollment Period start?
Your Medigap OEP begins the first month you are both age 65 or older AND enrolled in Medicare Part B. It lasts 6 months. During this window, you have a federal guaranteed-issue right to any Medigap plan sold in your state — no medical underwriting required.
Does the AEP give me a new Medigap guaranteed-issue right?
No. The Medicare Annual Enrollment Period (AEP, October 15 – December 7) applies to Medicare Advantage and Part D plans. It does not create a new Medigap Open Enrollment Period or guaranteed-issue right for most people. Medigap guaranteed-issue rights arise from specific qualifying events, not from AEP.
What if I delay Part B enrollment?
Delaying Part B without a qualifying Special Enrollment Period (such as active employer coverage) results in a permanent 10% late enrollment penalty per 12-month period you were eligible but not enrolled. It also delays the start of your Medigap OEP, which could affect your ability to get a Medigap plan without medical underwriting.
Which Medigap plan should I choose when transitioning from Marketplace coverage?
Plan G is the most comprehensive Medigap plan available to people newly eligible for Medicare (those who turned 65 on or after January 1, 2020). Plan N offers lower premiums with some cost sharing. High-Deductible Plan G provides catastrophic protection at the lowest monthly premium. The right choice depends on your health use patterns, budget, and travel habits. An independent broker can compare real-time rates from multiple carriers.
Ready to make the switch? Let's talk.
William Gray is an independent Medicare broker licensed in Florida and multiple states. He can walk you through your exact transition timeline, compare Medigap rates from multiple carriers, and help you protect your Medigap Open Enrollment Period.
Sources and disclosures
- Medicare.gov — Medicare Initial Enrollment Period
- Healthcare.gov — Medicare and the Marketplace
- CMS — Medigap Open Enrollment Period (42 U.S.C. § 1395ss)
- IRS — Premium Tax Credit eligibility and Medicare entitlement
- CMS — 2027 Part D deductible $700, OOP cap $2,400
This page is for educational purposes only and does not constitute insurance, legal, or tax advice. Coverage availability, benefits, and premiums vary by carrier, plan, and location. Consult a licensed professional before making Medicare coverage decisions.
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