You do not have to re-enroll in Original Medicare, but you must actively choose or change a Medicare Advantage or Part D plan every year if you want different coverage
Original Medicare (Part A and Part B) stays in place year after year once you sign up — you do not need to do anything to keep it. But if you have a Medicare Advantage plan (Part C) or a standalone prescription drug plan (Part D), your plan can change its costs, coverage, and pharmacy network every January 1st. If you do nothing during the annual enrollment period, you stay in your current plan, but that plan may no longer be the best fit for your medications, doctors, or budget.
The key date is the Annual Enrollment Period (AEP), which runs from October 15 to December 7 each year. During this window, you can switch plans, drop coverage, or add a plan you did not have before. If you miss this important date and want to make a change, you will generally have to wait until the next October, unless a life event (like moving, losing employer coverage, or a death in the household) opens a Special Enrollment Period.
Key Takeaways
- Original Medicare requires no annual re-enrollment — Part A and Part B coverage continues automatically each year.
- Medicare Advantage and Part D plans change every January 1st, so you should review your plan each October to December during the Annual Enrollment Period.
- If you do nothing during AEP, you stay in your current plan, but your costs and coverage may shift without notice.
- Missing the October 15 to December 7 important date usually means you cannot change plans until the following year, unless a life event qualifies you for a Special Enrollment Period.
Why Original Medicare does not require re-enrollment
Original Medicare is a defined benefit program — the coverage rules, deductibles, and coinsurance amounts are set by federal law and do not change from year to year (though Congress can alter them). Once you are enrolled in Part A (hospital insurance) and Part B (medical insurance), your coverage renews automatically on January 1st each year. You receive a new Medicare card in the mail, but you do not fill out forms or make choices.
This automatic renewal applies even if you move to a different state. Your Part A and Part B coverage follows you. The only reason you would need to take action is if you want to drop Part B (which requires a formal request and may trigger a penalty if you re-enroll later) or if you want to add a supplemental plan or Part D coverage, which are separate decisions.
How Medicare Advantage plans work differently
Medicare Advantage (Part C) is a private insurance alternative to Original Medicare. Each plan sets its own network of doctors and hospitals, its own copays and deductibles, and its own coverage rules. Because these details change annually, Medicare requires insurers to send you a notice of changes by September 30th each year. That notice tells you what is different for the coming year — higher copays, dropped doctors, new restrictions on specialist visits, or changes to your pharmacy network.
If you are happy with your plan and the changes do not affect you, you do nothing and stay enrolled. If the changes matter to you — your doctor is no longer in the network, your medications moved to a higher tier, or your out-of-pocket costs are rising — you can switch to a different Medicare Advantage plan or switch back to Original Medicare during the Annual Enrollment Period. You have until December 7th to make the change, and it takes effect January 1st.
If you miss the important date, you are locked into your current plan for the rest of the year. The only exception is if you experience a may have access to life event, such as moving out of your plan's service area, losing other health coverage, or having a change in your household.
Part D prescription drug plans and annual changes
Part D plans (standalone prescription drug coverage for people on Original Medicare, or built into some Medicare Advantage plans) also change every year. Your plan's formulary — the list of covered drugs — can shift, drugs can move to a higher cost tier, and pharmacy networks can shrink. A medication you paid $5 for this year might cost $50 next year under the same plan, or it might be removed from coverage entirely.
If you take regular medications, it is worth checking your plan's formulary each October. You can search by drug name on Medicare.gov or call your plan directly. If your current plan no longer covers your medications at an affordable cost, you can switch to a different Part D plan during AEP. If you are on Original Medicare and do not have Part D, you can also add it during this window — though waiting to enroll can result in a permanent late-enrollment penalty if you go without coverage for more than 63 days.
What happens if you do nothing during the Annual Enrollment Period
If you have a Medicare Advantage or Part D plan and take no action between October 15 and December 7, you automatically stay in your current plan for the next calendar year. Your coverage does not lapse, and you do not lose your insurance. However, your plan's costs and coverage will change on January 1st, and you may not realize it until you try to see a doctor or fill a prescription.
This passive renewal is intentional — it protects people who do not pay attention to the enrollment period. But it also means that if you are not actively reviewing your plan each year, you might end up paying more than you need to or losing access to your preferred doctors and pharmacies. Setting a calendar reminder for early October can help you avoid surprises.
Special Enrollment Periods for life changes
If you miss the Annual Enrollment Period but experience a may have access to event, you may be able to make changes outside the normal window. may have access to events include moving to a new state or out of your plan's service area, losing other health coverage (such as employer coverage or Medicaid), getting married or divorced, having a death in your household, or becoming may be able to access for Medicaid or Extra Help (a program that helps pay Part D costs).
When a may have access to event occurs, you typically have 60 days to make a change. You will need to contact Medicare directly or your plan to report the event and request a Special Enrollment Period. Keep documentation of the event — a lease showing your new address, a termination letter from your employer, or a death certificate — because Medicare will ask for proof.
How to review and compare your options each year
The easiest way to review your coverage is to use the Medicare Plan Finder tool on Medicare.gov. You enter your current medications, preferred doctors, and pharmacies, and the tool shows you all available plans in your area, ranked by estimated out-of-pocket costs. You can compare your current plan side by side with alternatives and see exactly how much you would save or spend by switching.
If you prefer to talk to someone, you can call 1-800-MEDICARE (1-800-633-4227) and speak with a Medicare counselor who can walk you through your options. Many states also have State Health Insurance information Programs (SHIPs) that offer free, one-on-one counseling. These counselors are trained to help you understand your choices and are not affiliated with any insurance company.
The best time to do this review is in early October, before the rush. If you wait until late November or early December, you may have longer hold times when calling for help, and you will have less time to think through your decision.
Frequently Asked Questions
What happens to my Original Medicare if I do not do anything during the enrollment period?
Your Original Medicare (Part A and Part B) continues automatically. You do not need to take any action. If you also have a Part D plan or Medicare Advantage, those are separate and may change, but your basic Medicare coverage stays the same.
Can I switch from Medicare Advantage back to Original Medicare after the enrollment period ends?
No, not unless you have a may have access to life event. If you miss the October 15 to December 7 window, you are locked into your Medicare Advantage plan until the next year's enrollment period. A may have access to event — such as moving out of your plan's service area — opens a 60-day window to switch.
If I switch plans during the enrollment period, when does my new plan start?
Your new plan takes effect on January 1st of the following year, regardless of when you switch during the October 15 to December 7 window. Your old plan ends on December 31st. Make sure you have your new plan information before January 1st so you know which doctors and pharmacies to use.
Do I have to re-enroll in Part D if I am happy with my plan and nothing changed?
No. If you do nothing, you stay in your current Part D plan. However, the plan's formulary, copays, and pharmacy network may change on January 1st, so it is still worth reviewing your plan in October to make sure your medications are still covered at a price you can afford.
What is the penalty for missing the Part D enrollment important date?
If you go without Part D coverage for more than 63 days after you first become may be able to access, you will owe a permanent late-enrollment penalty. The penalty is calculated based on the national average Part D premium and is added to your monthly Part D costs for as long as you have the coverage. The exact amount varies by year.