Medicare Enrollment Periods: When Can You Change Your Plan?
Short answer
The main window is the Medicare Annual Enrollment Period, which runs from October 15 to December 7 every year. During it, anyone with Medicare can join, switch or drop a Medicare Advantage plan or a Part D prescription drug plan. Changes you make take effect on January 1.
There are four other windows. The Medicare Advantage Open Enrollment Period (January 1 to March 31) lets people already in an Advantage plan make one change. The Initial Enrollment Period is the seven months around your 65th birthday. The General Enrollment Period (January 1 to March 31) is for people who missed signing up for Part B. Special Enrollment Periods open when something specific happens in your life, such as moving or losing employer coverage.
Outside these windows you generally cannot change plans, and missing some of them can create a penalty that stays on your premium for as long as you have Medicare.
The five enrollment windows at a glance
| Window | Dates | What you can do | Coverage starts |
|---|---|---|---|
| Annual Enrollment Period (AEP) | Oct 15 – Dec 7 | Join, switch or drop a Medicare Advantage plan; join, switch or drop a Part D plan; return to Original Medicare | January 1 |
| Medicare Advantage Open Enrollment | Jan 1 – Mar 31 | Only if you are already in an Advantage plan. Switch to a different Advantage plan once, or drop back to Original Medicare and add a Part D plan | First of the following month |
| Initial Enrollment Period (IEP) | 7 months around your 65th birthday | Enroll in Part A and Part B for the first time; join an Advantage or Part D plan | Depends on when in the window you enroll |
| General Enrollment Period (GEP) | Jan 1 – Mar 31 | Sign up for Part B if you missed your Initial Enrollment Period and have no Special Enrollment Period | First of the month after you enroll |
| Special Enrollment Period (SEP) | Triggered by an event | Varies by the event that triggered it | Varies |
The Annual Enrollment Period in detail
The AEP is the one that matters to most people who already have Medicare. From October 15 to December 7 you can:
- Switch from Original Medicare to a Medicare Advantage plan
- Switch from a Medicare Advantage plan back to Original Medicare
- Switch from one Medicare Advantage plan to another
- Join, change or drop a Part D prescription drug plan
You can make as many changes as you like during the window. The last change you make before December 7 is the one that takes effect on January 1.
What the Advantage Open Enrollment Period is not
The window from January 1 to March 31 is narrower than people expect. It is only for those already enrolled in a Medicare Advantage plan, it allows one change, and it does not let you switch from Original Medicare into an Advantage plan. If you are in Original Medicare on January 1, this window does nothing for you.
It also does not give you a guaranteed right to buy a Medigap policy. If you leave an Advantage plan during this window and want a Medigap policy, whether an insurer must sell you one depends on your state and your circumstances. See the switching warning in our Advantage vs Original Medicare comparison.
Turning 65: your Initial Enrollment Period
Your Initial Enrollment Period lasts seven months: the three months before the month you turn 65, your birthday month, and the three months after. Enrolling in the three months before your birthday month generally means your coverage starts at the beginning of your birthday month. Enrolling later delays the start.
If you are already receiving Social Security benefits, you are usually enrolled in Part A and Part B automatically. If you are not, you have to sign up yourself — nobody does it for you, and this is where most late enrollment penalties begin.
What happens if you miss a deadline
Part B late enrollment penalty
If you were not covered by qualifying employer insurance and you did not sign up for Part B when you were first eligible, your monthly premium can increase by 10% for each full 12-month period you could have had Part B but did not. In most cases this penalty lasts for as long as you have Part B.
Part D late enrollment penalty
If you go 63 days or more in a row without Part D or other creditable prescription drug coverage after your Initial Enrollment Period, a permanent amount is added to your Part D premium. It is calculated from the number of months you went without coverage and the national base beneficiary premium, which changes each year.
Both penalties are avoidable and neither is easy to remove afterwards. If you are approaching 65 and still working, check whether your employer coverage counts as creditable before your birthday, not after.
Special Enrollment Periods
Life events can open a window outside the normal calendar. Common triggers include:
- Moving out of your plan's service area, or moving to an area with new plan options
- Losing employer or union coverage
- Your plan leaving Medicare or ending its contract in your area
- Moving into, living in, or leaving a skilled nursing facility or long-term care facility
- Qualifying for Medicaid or Extra Help, or losing that eligibility
Rules and time limits differ by trigger, and some Special Enrollment Periods have been narrowed in recent years. Confirm your specific situation at Medicare.gov or with a licensed agent before assuming you qualify.
Frequently asked questions
When is the Medicare Annual Enrollment Period?
October 15 to December 7 every year. Any change you make takes effect on January 1 of the following year.
I missed the December 7 deadline. What can I do now?
It depends on what coverage you have. If you are already in a Medicare Advantage plan, the Medicare Advantage Open Enrollment Period from January 1 to March 31 lets you make one change. If you are in Original Medicare and need Part B, the General Enrollment Period from January 1 to March 31 applies, though a late enrollment penalty may apply. Otherwise you may qualify for a Special Enrollment Period if you have had a qualifying life event, such as a move or a loss of employer coverage. If none of those apply, the next Annual Enrollment Period is your next opportunity.
Can I change my Medicare plan at any time?
No. Outside the defined enrollment windows you generally cannot switch plans. This is the most common misunderstanding about Medicare, and it is why the Annual Notice of Change your plan sends in September is worth reading carefully.
How many times can I change plans during the Annual Enrollment Period?
As many times as you want between October 15 and December 7. Only the last change you make is the one that takes effect on January 1.
Do I need to re-enroll in my Medicare plan every year?
Usually no. Most plans renew automatically. But automatic renewal does not mean the plan stays the same — premiums, copays, drug coverage and provider networks can all change on January 1. Doing nothing is a decision, not a way of avoiding one.
Does the Annual Enrollment Period apply to Medigap policies?
No. Medigap has its own rules. Your strongest guaranteed right to buy a Medigap policy is normally during your Medigap open enrollment period, which typically begins when you are 65 or older and enrolled in Part B. Outside that, insurers in many states may use medical underwriting.
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