Medicare · Cornerstone
Medicare enrollment periods
Last reviewed June 11, 20265 min readBy the Goodsurance editorial team Reviewed by the Goodsurance editorial team
Medicare has several enrollment periods, each with its own initials, and they get mixed up constantly because the acronyms sound interchangeable and the dates overlap. They are not interchangeable. Each one lets you do different things, and using the wrong window for the change you want, or assuming a window lets you do something it does not, is one of the more common Medicare mistakes. Here is each one in plain terms, with what it is actually for and where people trip.
1IEP: your Initial Enrollment Period
This is your first window, built around your 65th birthday. It runs seven months: the three months before your birthday month, the month itself, and the three months after. This is when you first sign up for Parts A and B, and when you can add a drug plan or a supplement without trouble.
The timing inside the window matters more than people expect. Enroll in the three months before your birthday month and coverage generally starts the first of your birthday month. Wait until your birthday month or later, and the start date pushes back, leaving a gap. Miss the IEP entirely and you are looking at the General Enrollment Period below, usually with a penalty.
There is also a related guarantee worth knowing: your six-month Medigap Open Enrollment window, the one time you can buy any supplement without a health review, is keyed to when you are 65 and enrolled in Part B. It is a separate clock from the IEP, but they often run together.
The Medicare year at a glance
2AEP: the Annual Election Period
This is the big one, the window most people mean when they say "open enrollment." It runs October 15 to December 7 every year, and changes you make take effect January 1.
During AEP you can switch from Original Medicare to a Medicare Advantage plan or the reverse, switch from one Advantage plan to another, and join, drop, or change a Part D drug plan. It is also the period buried under a mountain of television advertising every fall, which is precisely when it helps to know what you actually want before you pick up the phone.
One thing AEP does not do, a common misread: it does not give you a guaranteed right to buy a Medigap supplement without medical underwriting. AEP is about Advantage and Part D. If you are on Advantage and want to move back to Original plus a Medigap policy, you can change the Advantage side during AEP, but the Medigap carrier can still review your health and decline you unless a separate guaranteed-issue right applies.
AEP is about Advantage and Part D. It does not give you a guaranteed right to buy a Medigap supplement without medical underwriting. You can change the Advantage side during AEP, but a Medigap carrier can still review your health and decline you unless a separate guaranteed-issue right applies.
3MA-OEP: the Medicare Advantage Open Enrollment Period
This one is narrower and only for people already in a Medicare Advantage plan as of January 1. It runs January 1 to March 31, and it gives you one chance to make a single change: switch to a different Advantage plan, or drop Advantage and go back to Original Medicare (adding a drug plan if you do).
It exists as a safety valve. You picked an Advantage plan during AEP, the new plan year started, and something is not working, the wrong network, a drug not covered the way you expected. Two limits worth knowing: it is one change, not unlimited shopping, and it is only for people already in an Advantage plan. If you are on Original Medicare on January 1, you cannot use MA-OEP to jump into Advantage.
4GEP: the General Enrollment Period
This is the catch-up window for people who missed their IEP and do not qualify for a Special Enrollment Period. It runs January 1 to March 31, with coverage starting the month after you enroll.
The GEP gets you in, but it is the expensive door. If you are here because you missed your IEP without qualifying coverage, the permanent Part B late-enrollment penalty usually comes with it, and you may have waited months with no coverage to reach this window. It is a real path back, just not a free one.
5SEP: Special Enrollment Periods
These are the exception windows, triggered by life events rather than the calendar, and there are more of them than most people realize.
The best known is leaving employer coverage: if you delayed Part B while still working at a company with 20 or more employees, you get a Special Enrollment Period to sign up without penalty after your employment or that coverage ends, whichever comes first. COBRA does not extend the window. But SEPs cover many situations:
- Moving out of your plan's service area, which opens a window to pick a new plan.
- Losing other coverage you were relying on, including a plan that leaves the market.
- Qualifying for Extra Help or Medicaid, which comes with ongoing flexibility to change drug or Advantage plans.
- A "5-star" SEP, a once-a-year chance to switch into a plan that earned Medicare's top quality rating, if one is offered in your area.
Each has its own rules and clock. The reason SEPs matter so much is that they are often the difference between enrolling or switching late with a penalty and doing it with none, and which one applies depends entirely on your situation. If a major life change has happened, it is worth checking whether it opened a window.
6Holding it together
The thing to hold onto: IEP is your first window at 65, AEP is the annual change window for everyone, MA-OEP is a one-time do-over for current Advantage members early in the year, GEP is the penalty-prone catch-up, and SEPs are the life-event exceptions that can save you from a penalty or open an off-cycle change. When in doubt about which one fits the change you want, it is worth checking before you act, because the windows do not forgive much, and the most expensive mistakes here come from assuming a window does something it does not.
| Window | Who | What you can do | Penalty |
|---|---|---|---|
| IEP | New to Medicare at 65 | First sign-up for A, B, D, Medigap | None if on time |
| AEP | Everyone, each fall | Change Advantage or Part D | None |
| MA-OEP | Advantage members | One switch, or back to Original | None |
| GEP | Missed your IEP | Catch-up enroll in A and B | Likely |
| SEP | After a qualifying life event | Enroll or switch off-cycle | Usually none |
Match the change you want to the right window. Source: CMS.
Common questions about Medicare
Quick answers to common questions
Tap any question to expand. Each question links to a fuller standalone answer.
When can I enroll in Medicare?
Most people can first enroll in Medicare during their Initial Enrollment Period, a seven-month window around your 65th birthday that starts three months before the month you turn 65, includes that month, and ends three months after.
If you miss it, the General Enrollment Period runs January 1 to March 31 each year for Part A and Part B. After you have Medicare, the Annual Enrollment Period from October 15 to December 7 (2026) lets you change Part D drug plans and Medicare Advantage plans, with changes effective January 1. The Medicare Advantage Open Enrollment Period from January 1 to March 31 (2026) lets people already in a Medicare Advantage plan switch once. Special Enrollment Periods may also apply after certain life events, like losing job coverage. To review which window fits you, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
What is AEP in Medicare?
AEP stands for the Annual Enrollment Period, the yearly window when anyone with Medicare can make changes to their coverage.
It runs from October 15 to December 7 (2026), and the changes you make take effect January 1 of the following year. During AEP you can join, switch, or drop a Medicare Advantage plan (Part C), join, switch, or drop a Part D prescription drug plan, and move between Original Medicare and Medicare Advantage. This is the main once-a-year opportunity to review your plan against your current doctors, medications, and budget, since plans can change their costs and coverage each year. AEP is different from the Medicare Advantage Open Enrollment Period, which runs January 1 to March 31 (2026) and only lets people already in a Medicare Advantage plan make one switch. If you want to change plans, AEP is usually the time to do it.
What is the Medicare Open Enrollment Period?
The term Medicare Open Enrollment Period is used two ways, so it helps to be specific.
Most often people mean the Annual Enrollment Period (AEP), which runs October 15 to December 7 (2026) and lets anyone with Medicare join, switch, or drop a Medicare Advantage plan (Part C) or a Part D drug plan, with changes effective January 1. Separately, the Medicare Advantage Open Enrollment Period runs January 1 to March 31 (2026) and lets people already enrolled in a Medicare Advantage plan make one change, such as switching to another Medicare Advantage plan or returning to Original Medicare. There is also a Medigap Open Enrollment Period, a six-month window that begins when you are 65 or older and enrolled in Part B, during which you can buy a Medigap (supplement) policy without health-based pricing. Knowing which one you mean determines what you can change.
Can I change my Medicare Advantage plan in January?
Yes.
If you are already in a Medicare Advantage plan (Part C, your Medicare benefits through a private plan), the Medicare Advantage Open Enrollment Period lets you make one change between January 1 and March 31 (2026). During this window you can switch to a different Medicare Advantage plan, or leave Medicare Advantage and return to Original Medicare, and if you return to Original Medicare you can also add a Part D drug plan. This window is only for people who already have a Medicare Advantage plan on January 1; it is not a time to switch from Original Medicare into Medicare Advantage. You get one change during this period, and it takes effect the first of the month after the plan receives your request. This is separate from the Annual Enrollment Period, which runs October 15 to December 7 (2026). If you missed making a change during AEP, the January to March window is a second chance for current Medicare Advantage members.
How do I sign up for Medicare?
You sign up for Medicare through Social Security, online at ssa.gov, by phone, or in person at a Social Security office; Medicare itself does not handle enrollment.
The best time is your Initial Enrollment Period, the seven-month window around your 65th birthday. If you already receive Social Security benefits, you are usually enrolled automatically in Part A and Part B. If you are not yet drawing Social Security, you have to apply yourself. After you have Part A and Part B, you can separately choose added coverage like a Part D drug plan, a Medicare Advantage plan, or a Medigap supplement. To talk through which added coverage fits your situation, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
Is Medicare automatic at 65?
Medicare is not automatic for everyone at 65; it depends on whether you already receive Social Security.
If you are drawing Social Security or Railroad Retirement benefits before 65, you are usually enrolled automatically in Part A (hospital) and Part B (medical), and your card arrives a few months before your birthday. If you have not started those benefits, enrollment is not automatic, and you must apply yourself through Social Security during your Initial Enrollment Period, the seven-month window around your 65th birthday. People who qualify through disability are often enrolled automatically after 24 months of benefits. Even when Part A and B are automatic, drug coverage and other plan choices are not. To review your options, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
Where do I enroll in Medicare?
You enroll in Medicare through the Social Security Administration, not through Medicare directly.
You can apply online at ssa.gov, by phone, or in person at a local Social Security office. Railroad retirees apply through the Railroad Retirement Board instead. This applies to Part A (hospital) and Part B (medical). Added coverage works differently: you enroll in a Part D drug plan, a Medicare Advantage plan, or a Medigap supplement through the insurance company offering it or with help from a licensed agent, not through Social Security. Knowing which door to use saves time and helps avoid gaps. To get help choosing and enrolling in added coverage, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
Do I need to sign up for Medicare if I have other insurance?
It depends on the kind of other insurance you have.
If you have active employer coverage through a job with 20 or more employees, where you or your spouse still work, you can usually delay Medicare without penalty and sign up later through a Special Enrollment Period. If your employer has fewer than 20 employees, Medicare often becomes the primary payer, so you typically need to enroll at 65 to avoid gaps. Retiree coverage, COBRA, and marketplace plans generally do not count as active employer coverage, so delaying Medicare with those can trigger a late penalty. The rules turn on whether the coverage is active and the employer's size. To check your specific situation, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
How long does it take to get Medicare after applying?
Coverage timing depends on when you apply within your enrollment window.
If you sign up during the three months before your 65th birthday, your Part A and Part B coverage generally start the first day of your birthday month. If you apply during or after your birthday month, your start date can be delayed by a month or more. Once Social Security processes your application, your Medicare card typically arrives by mail within a few weeks, though it can take longer during busy periods. Applying early in your Initial Enrollment Period, the seven-month window around your 65th birthday, is the best way to avoid a gap in coverage. To plan your timing, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
What is the Part B late penalty?
The Part B late penalty is a permanent surcharge added to your Part B (medical) monthly premium if you delay enrolling without qualifying coverage.
The penalty is 10% of the standard premium for each full 12 months you could have had Part B but did not sign up. Because it is based on full 12-month periods, waiting two full years would add 20%, and so on. The surcharge is permanent, meaning it stays on your premium for as long as you have Part B, not just for a year. You can avoid it by enrolling during your Initial Enrollment Period or by having qualifying coverage, like active employer insurance, that lets you delay. To check whether a penalty applies to you, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
How much is the Part B penalty?
The Part B penalty adds 10% to your Part B (medical) premium for each full 12 months you could have enrolled but did not.
So one full year late adds 10%, two full years adds 20%, and it keeps climbing with each additional full year of delay. The penalty is calculated as a percentage of the standard premium, which is $202.90 per month in 2026, and the surcharge is permanent: it stays on your premium for as long as you have Part B. Because the base premium can change from year to year, the dollar amount of your penalty can shift too, but the percentage tied to your delay stays the same. To work out what a penalty would mean for you, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
Can I avoid the Part B penalty?
Yes, you can avoid the Part B (medical) penalty by enrolling on time or by having qualifying coverage that lets you delay.
The simplest way is to sign up during your Initial Enrollment Period, the seven-month window around your 65th birthday. If you keep working past 65 and have active employer coverage through a job with 20 or more employees, you can delay Part B without penalty and enroll later using a Special Enrollment Period, which gives you 8 months after that employment or coverage ends, whichever comes first. Watch out: retiree coverage, COBRA, and marketplace plans do not count as qualifying coverage for this purpose, so delaying with those can trigger the penalty. To confirm your coverage qualifies, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.
References
- Medicare.govAll the enrollment periods and what each permits.
- CMS, Centers for Medicare & Medicaid ServicesFederal definitions and Special Enrollment Period triggers. cms.gov
- SSA, Social Security AdministrationPart B enrollment timing and penalties. ssa.gov