Medicare Enrollment Periods Explained: IEP, GEP, OEP & AEP

Quick Reference: All Medicare Enrollment Periods

IEP — Initial Enrollment Period

The IEP is the most important enrollment window for most people. It is a 7-month period centered on your 65th birthday:

• Months 1–3: The 3 months before your birth month
• Month 4: Your birth month
• Months 5–7: The 3 months after your birth month

What you can enroll in during your IEP:

• Part A (hospital insurance) — usually premium-free if you or your spouse paid Medicare taxes for 10+ years
• Part B (medical insurance) — standard premium is $185/month in 2026
• Medicare Advantage (Part C) — bundles Part A, Part B, and usually Part D through a private insurer
• Part D (prescription drug coverage) — standalone plans if you stay on Original Medicare
• Medigap (Medicare Supplement) — your Medigap Open Enrollment also starts when Part B begins

When coverage starts depends on when you sign up:

• Sign up in the 3 months before your birth month → coverage starts the 1st of your birth month
• Sign up during your birth month → coverage starts the 1st of the following month
• Sign up in the 3 months after your birth month → coverage is delayed 1–3 months

The earlier you enroll during your IEP, the sooner your coverage starts. There's no advantage to waiting.

Set a deadline reminder so you don't miss your IEP →

AEP — Annual Enrollment Period

The AEP runs every year from October 15 through December 7. All changes made during AEP take effect January 1 of the following year.

During AEP you can:

• Switch from one Medicare Advantage plan to another
• Switch from Original Medicare to Medicare Advantage
• Drop Medicare Advantage and go back to Original Medicare
• Join a Part D plan
• Switch Part D plans
• Drop Part D coverage (not usually recommended)

AEP is the busiest time in Medicare. If you have a Medicare Advantage or Part D plan, this is the time to compare your current plan against alternatives for the coming year.

Compare Medicare Advantage plans →

Compare Part D drug plans →

OEP — Medicare Advantage Open Enrollment Period

The OEP runs from January 1 through March 31 each year. Despite the similar name, this is completely different from AEP.

Who can use OEP: Only people who are currently enrolled in a Medicare Advantage plan as of January 1.

During OEP you can:

• Switch from one Medicare Advantage plan to a different Medicare Advantage plan
• Drop your Medicare Advantage plan and return to Original Medicare (and join a standalone Part D plan)

OEP limitations:

• You get one change — once you make it, your OEP is done for the year
• You cannot use OEP to go from Original Medicare to Medicare Advantage (that requires AEP or a SEP)
• Changes take effect the first of the month after your plan receives the request

If you made an AEP choice you regret, OEP is your safety valve — but keep in mind that if you drop Medicare Advantage for Original Medicare during OEP, getting a Medigap policy may require medical underwriting (depending on your state).

Compare Medigap plans →

GEP — General Enrollment Period

The GEP runs from January 1 through March 31 each year. It exists for people who missed their Initial Enrollment Period and don't qualify for a Special Enrollment Period.

During GEP you can:

• Sign up for Part A (if you didn't enroll automatically)
• Sign up for Part B

Key details:

• Coverage doesn't start until July 1 of that year — meaning a gap of 3–6 months without coverage
• You may face late enrollment penalties:
  • Part B penalty: 10% added to your monthly premium for each full 12-month period you were eligible but didn't enroll. This penalty is permanent. Full penalty guide →
  • Part D penalty: 1% of the national base beneficiary premium for each month you went without creditable drug coverage

Missed your enrollment window? See all your options →

SEPs — Special Enrollment Periods

Special Enrollment Periods let you enroll in or change Medicare coverage outside the normal enrollment windows when you experience a qualifying life event.

Common SEPs include:

• Loss of employer coverage: You get 8 months to sign up for Part B after losing employer group health coverage (or after employment ends, whichever comes first). This is the most common SEP. Working past 65 with employer coverage →
• Moving to a new area: If you move out of your plan's service area, you get a SEP to choose a new plan available in your new location
• Qualifying for Extra Help (LIS): If you become eligible for the Low-Income Subsidy, you get a SEP to switch Part D plans once per quarter
• 5-star plan SEP: You can switch to a Medicare Advantage or Part D plan with a 5-star quality rating once per year (Dec 8 – Nov 30)
• Plan contract termination: If your plan leaves Medicare or stops serving your area, you get a SEP to choose a new plan
• Institutional SEP: If you move into or out of a nursing home or other institution, you get a SEP each month
• COBRA ending: Note that COBRA coverage does not count as employer coverage for Part B SEP purposes. The COBRA penalty trap →

Medigap Open Enrollment Period

The Medigap Open Enrollment Period is a one-time, 6-month window that starts the month your Medicare Part B coverage begins (typically when you turn 65).

Why this window matters:

• During this period, you have guaranteed issue rights — insurance companies must sell you any Medigap plan they offer, regardless of your health
• They cannot charge you more due to pre-existing conditions
• They cannot deny you coverage

After this window closes:

• Insurers can use medical underwriting — they can deny coverage or charge higher premiums based on health conditions
• Some states offer additional protections (e.g., Connecticut, Massachusetts, Maine, New York guarantee Medigap access year-round), but most do not

Compare Medigap plans in your area →

Enrollment Period Timeline: How They Fit Together

Here's how the enrollment periods map across a typical calendar year (2026):

Your IEP and Medigap Open Enrollment are personal — they depend on when you turn 65 and when Part B starts, not the calendar.

Frequently Asked Questions