The Six Medicare Enrollment Windows Six Windows

How to use this guide

Medicare does not run on a single enrollment window. It runs on six distinct windows, each with its own rules, eligibility conditions, and consequences for missing it. Most guides focus on the Annual Enrollment Period — the one with the television ads every fall — but AEP is actually the least consequential window for most people making their first Medicare decisions. Which window applies to you depends on three things: your age (specifically, whether you are approaching 65 or already past it), your current coverage (employer coverage, VA benefits, or nothing), and your state (a handful of states have year-round or expanded protections that change the calculus significantly).

The window most people don’t hear about until it’s too late is the Medigap Open Enrollment Period. Unlike every other window in this guide, it opens once and does not automatically reopen. It is six months long, tied to your Part B enrollment date, and it determines whether you can buy comprehensive supplemental coverage without answering health questions. Understand this window first. Then read the others.

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Initial Enrollment Period (IEP)

The IEP is your first opportunity to enroll in Medicare. It is seven months long: the three months before the month you turn 65, the month you turn 65, and the three months after. This is when you can sign up for Part A (hospital insurance) and Part B (medical insurance). Most people get Part A without a premium because of their work history — but Part B has a standard monthly premium, and enrolling on time matters.

If you miss your IEP and do not have qualifying employer coverage as a reason for delay, you will generally need to wait for the General Enrollment Period (January 1 to March 31), and you may owe a permanent late-enrollment penalty on Part B: 10% of the standard premium for every 12-month period you delayed. That penalty follows you for as long as you have Medicare.

When	3 months before your 65th birthday month through 3 months after
Duration	7 months
What you can do	Enroll in Part A and/or Part B for the first time
Penalty if missed	Permanent 10% Part B premium surcharge per 12 months of delay (unless you have qualifying employer coverage)

Source: Medicare.gov — “When can I sign up for Medicare?”

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Medigap Open Enrollment Period

The Medigap Open Enrollment Period is six months long. It begins the month you are both 65 or older AND enrolled in Medicare Part B. During this window, any insurance company that sells Medigap in your state must offer you any policy they sell, at the same price they charge a healthy person your age, without medical underwriting. They cannot ask about your health history. They cannot charge you more because of a pre-existing condition. They cannot deny you.

After this window closes, in most states, that protection ends. Insurers can ask medical questions, decline to sell you a policy, or quote a substantially higher premium. This is the window that organizes the rest of the Medicare decision — because the choice between Original Medicare with Medigap and Medicare Advantage is, at its core, a question of whether you want to protect this window while you have it.

When	Starts the month you are 65+ AND enrolled in Part B
Duration	6 months, opens once (no automatic renewal in most states)
What you can do	Buy any Medigap policy sold in your state, guaranteed issue, no underwriting
Penalty if missed	No federal penalty, but insurers can deny coverage or charge higher premiums in most states after the window closes

Source: Medicare.gov — “When can I buy Medigap?”

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Annual Enrollment Period (AEP)

The AEP runs from October 15 to December 7 every year. It is the window most Medicare beneficiaries have heard of — the one that produces the television advertisements each fall. During AEP, anyone with Medicare can switch from one Medicare Advantage plan to another, switch from Medicare Advantage to Original Medicare (with a standalone Part D plan), switch from Original Medicare to Medicare Advantage, or change their standalone Part D prescription drug plan. Changes made during AEP take effect January 1 of the following year.

AEP matters most for people who are already enrolled and want to review their coverage for the upcoming year. It is not the same as the Medigap Open Enrollment Period. Switching to Original Medicare during AEP does not restore your Medigap guaranteed-issue rights in most states.

When	October 15 to December 7, every year
Duration	54 days
What you can do	Switch between Medicare Advantage plans, switch between MA and Original Medicare, change Part D plan
Penalty if missed	No penalty for missing AEP — you remain in your current coverage until the next AEP

Source: Medicare.gov — “When can I sign up for Medicare?”

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Medicare Advantage Open Enrollment Period (MA-OEP)

The MA-OEP runs from January 1 to March 31 each year, but it is only available to people who are already enrolled in a Medicare Advantage plan. During this window, an MA enrollee can make one switch: to a different Medicare Advantage plan, or back to Original Medicare (with the option to add a standalone Part D plan). Only one change is permitted per MA-OEP.

The MA-OEP is narrower than it looks. It does not restore Medigap guaranteed-issue rights in most states — so returning to Original Medicare during MA-OEP may mean you cannot obtain Medigap coverage without medical underwriting. If you are considering leaving Medicare Advantage and returning to Original Medicare with Medigap, understanding your state’s rules before acting during MA-OEP is essential.

When	January 1 to March 31, every year
Duration	90 days
What you can do	One switch: to another MA plan, or to Original Medicare + Part D (MA enrollees only)
Penalty if missed	No penalty — you remain in your current MA plan until the next opportunity

Source: CMS — “Medicare Advantage Open Enrollment Period”

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General Enrollment Period (GEP)

The GEP runs from January 1 to March 31 each year. It is for people who missed their Initial Enrollment Period and do not have a qualifying reason (like active employer coverage) for the delay. Enrolling during GEP means coverage begins the month after enrollment — so a March enrollment means April coverage. People who enroll during GEP may also owe a permanent Part B late-enrollment penalty.

The GEP overlaps with the MA-OEP calendar dates (both run January through March), but they serve different populations: GEP is for first-time enrollees who missed IEP, while MA-OEP is for people already in Medicare Advantage who want to switch.

When	January 1 to March 31, every year
Duration	90 days
What you can do	Enroll in Part A and/or Part B for the first time (for those who missed IEP without qualifying employer coverage)
Penalty if missed	Permanent 10% Part B premium surcharge per 12-month period of delay

Source: Medicare.gov — “When can I sign up for Medicare?”

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Special Enrollment Periods (SEPs)

SEPs are triggered by specific life events rather than calendar dates. They allow you to make Medicare changes outside of the standard windows when a qualifying event occurs. The most common SEP triggers include: losing employer-sponsored health coverage (or your employer’s coverage becoming secondary), moving out of your plan’s service area, qualifying for Extra Help (Low Income Subsidy) or Medicaid, your plan being terminated or losing its Medicare contract, or returning to the United States after living abroad.

The duration of an SEP varies by trigger. Losing employer coverage, for example, typically gives you an eight-month window to enroll in Part B without a late-enrollment penalty. The specifics of each SEP — when it starts, how long it lasts, what it allows — depend on the triggering event.

When	Triggered by a qualifying life event
Duration	Varies by trigger (commonly 2–8 months from the triggering event)
What you can do	Enroll in Medicare, switch plans, or make other changes specific to the qualifying event
Penalty if missed	May lose SEP protection; standard enrollment rules and penalties may apply

Source: Medicare.gov — “When can I sign up for Medicare?”; for plain-language SEP trigger descriptions, see the Medicare Rights Center

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A note on state variation

A handful of states have extended or modified the standard federal rules in ways that significantly change the analysis above.

Four states — Connecticut, Maine, Massachusetts, and New York — require insurance companies to offer guaranteed-issue Medigap coverage year-round, regardless of age or health status. In these states, the Medigap Open Enrollment Period is less urgent because the window never fully closes. Vermont and Washington offer partial year-round protections with some restrictions on which plans are available.

A growing number of states have adopted “birthday rules” that open a brief window — typically 30 to 63 days — around your birthday each year, allowing you to switch Medigap plans without medical underwriting. As of 2026, these states include California, Idaho, Illinois, Kentucky, Louisiana, Nevada, and Oregon, among others. Birthday-rule windows are narrower than the original six-month OEP and usually restrict which plans you can switch to, but they provide a partial second chance for people in MA who want to return to Original Medicare.

For state-specific rules, Medicare.gov’s state resources and your state’s SHIP counselor are the most accurate sources. State laws change, and the birthday-rule list has been expanding.