Medicare has multiple enrollment periods, each with its own rules about when you can sign up or make changes. Understanding these windows is crucial because enrolling at the wrong time—or missing your window entirely—can result in penalties, coverage gaps, or being locked into a plan you don't want.
This guide covers every Medicare enrollment period so you know exactly when you can take action.
Enrollment Periods at a Glance
Here's a quick overview of the main Medicare enrollment periods:
- Initial Enrollment Period (IEP): Your first chance to enroll when you turn 65
- General Enrollment Period (GEP): Annual window if you missed your IEP
- Special Enrollment Periods (SEP): Triggered by qualifying life events
- Open Enrollment Period (OEP): Annual window to change Medicare Advantage or Part D plans
- Medicare Advantage Open Enrollment: Early-year window for MA enrollees to switch
- Medigap Open Enrollment: Your 6-month window for guaranteed Medigap access
Initial Enrollment Period (IEP)
Initial Enrollment Period
This is your first and best opportunity to enroll in Medicare Parts A and B. The 7-month window includes:
- 3 months before your 65th birthday month
- Your birthday month
- 3 months after your birthday month
When Does Coverage Start?
Your coverage start date depends on when you enroll during your IEP:
- Enroll 3 months before birthday: Coverage starts the 1st of your birthday month
- Enroll during birthday month: Coverage starts the 1st of the following month
- Enroll 1 month after birthday: Coverage starts 2 months later
- Enroll 2-3 months after birthday: Coverage starts 3 months later
Best Practice
Enroll during the 3 months before your 65th birthday to ensure your coverage starts right when you turn 65, with no gap in protection.
What If You're Still Working?
If you have health insurance through your employer (or your spouse's employer) with 20+ employees, you can delay Medicare enrollment without penalty. You'll qualify for a Special Enrollment Period when that coverage ends.
General Enrollment Period (GEP)
General Enrollment Period
If you missed your Initial Enrollment Period and don't qualify for a Special Enrollment Period, this is your annual window to sign up for Medicare Parts A and B.
GEP Comes with Consequences
Enrolling during the General Enrollment Period means you'll likely pay late enrollment penalties, and your coverage won't start until July 1st. Avoid the GEP if possible by enrolling during your IEP or qualifying for a SEP.
GEP Key Points
- Coverage start date: July 1st of the same year
- Penalties: You'll pay the Part B late penalty (10% for every 12-month period you could have had Part B but didn't)
- Who uses it: People who missed their IEP and don't qualify for a SEP
Special Enrollment Periods (SEP)
Special Enrollment Periods
Special Enrollment Periods are triggered by specific life events that give you the opportunity to enroll in or change your Medicare coverage outside of regular enrollment windows.
Common SEP Triggers
Loss of Employer Coverage
If you delayed Medicare because you had coverage through an employer with 20+ employees, you qualify for a SEP when:
- Your employment ends
- Your employer coverage ends
- Your employer reduces workforce below 20 employees
Timeframe: 8 months from the date employment or coverage ends (whichever comes first)
Moving to a New Area
If you move to an area where your current Medicare Advantage or Part D plan isn't available, you can switch plans.
Timeframe: Generally 2 months after you move
Leaving a Medicare Advantage Plan
Certain situations allow you to leave a Medicare Advantage plan and return to Original Medicare:
- Moving out of your plan's service area
- Plan is terminated or reduces service area
- Qualifying for Medicaid
- Entering a skilled nursing facility
5-Star Plan SEP
You can switch to a Medicare Advantage or Part D plan with a 5-star rating once per year, outside of regular enrollment periods.
Important: COBRA Doesn't Count
COBRA coverage does NOT qualify you for a Special Enrollment Period. If you're on COBRA when you turn 65, you should enroll in Medicare during your Initial Enrollment Period to avoid penalties.
Open Enrollment Period (OEP) / Annual Election Period
Medicare Open Enrollment (Annual Election Period)
This is the annual window to review and change your Medicare Advantage and/or Part D coverage for the following year. Changes take effect January 1st.
What You Can Do During Open Enrollment
- Switch from Original Medicare to a Medicare Advantage plan
- Switch from a Medicare Advantage plan to Original Medicare
- Switch from one Medicare Advantage plan to another
- Join a Medicare Part D prescription drug plan
- Switch from one Part D plan to another
- Drop your Part D coverage (not recommended)
What You Cannot Do
- Enroll in Medicare Parts A or B for the first time (that's the IEP or GEP)
- Buy or change a Medigap policy (different rules apply)
Review Your Coverage Every Year
Plans change their costs, coverage, and drug formularies annually. Even if you're happy with your current plan, review the Annual Notice of Change document you receive in September to make sure it still meets your needs.
Medicare Advantage Open Enrollment Period
Medicare Advantage Open Enrollment Period
This window is exclusively for people already enrolled in a Medicare Advantage plan. It allows you to make one plan change.
What You Can Do
- Switch to a different Medicare Advantage plan
- Drop your Medicare Advantage plan and return to Original Medicare
- If you return to Original Medicare, you can also join a standalone Part D plan
What You Cannot Do
- Switch from Original Medicare to a Medicare Advantage plan (that's the fall OEP)
- Join Medicare for the first time
- Make multiple changes (only one change allowed during this period)
Medigap Open Enrollment Period
Medigap Open Enrollment Period
This is your one-time window to buy any Medigap policy sold in your state, regardless of health conditions. Insurance companies cannot deny you or charge you more due to pre-existing conditions during this period.
Critical: Don't Miss This Window
After your 6-month Medigap Open Enrollment Period ends, insurance companies can use medical underwriting. They can deny you coverage or charge significantly higher premiums based on your health. This window only happens once.
When Does It Start?
Your Medigap Open Enrollment Period begins on the first day of the month in which you are:
- 65 years old or older, AND
- Enrolled in Medicare Part B
Example: If you turn 65 in March and Part B starts March 1st, your Medigap window is March 1st through August 31st.
What's Guaranteed During This Window
- You can buy any Medigap policy sold in your state
- You pay the same price as someone in perfect health
- Pre-existing conditions cannot be permanently excluded (though there may be a waiting period for conditions treated in the 6 months before coverage starts)
Part D Enrollment Windows
Initial Part D Enrollment
Your Initial Enrollment Period for Part D is the same as your Initial Enrollment Period for Parts A and B: the 7 months around your 65th birthday.
Changing Part D Plans
You can change your Part D plan during:
- Open Enrollment Period: October 15 - December 7
- Special Enrollment Periods: When you have a qualifying life event
Part D Late Enrollment Penalty
If you don't enroll in Part D when first eligible and don't have creditable drug coverage (coverage as good as Medicare's), you'll pay a penalty:
- 1% of the national base beneficiary premium for every month you didn't have coverage
- This penalty is permanent and added to your monthly Part D premium
- Example: 24 months without coverage = 24% penalty on your monthly premium, for life
Late Enrollment Penalties
Part B Late Enrollment Penalty
- Amount: 10% of the standard premium for every 12-month period you could have had Part B but didn't
- Duration: You pay this penalty for as long as you have Part B
- Example: If you delayed Part B for 3 years without qualifying coverage, you'd pay a 30% penalty on your monthly premium for life
Part D Late Enrollment Penalty
- Amount: 1% of the national base beneficiary premium for every month you were without creditable drug coverage
- Duration: Permanent, added to your monthly Part D premium
- Example: 18 months without coverage = 18% penalty
How to Avoid Penalties
Enroll during your Initial Enrollment Period, or make sure you have qualifying coverage (employer insurance for Part B, creditable drug coverage for Part D) that allows you to delay enrollment without penalty.
Quick Reference Table
| Enrollment Period | Dates | What You Can Do |
|---|---|---|
| Initial Enrollment (IEP) | 7 months around 65th birthday | Enroll in Parts A, B, C, D; buy Medigap |
| General Enrollment (GEP) | Jan 1 - Mar 31 | Enroll in Parts A & B if you missed IEP |
| Special Enrollment (SEP) | Varies by event | Enroll/change due to qualifying event |
| Open Enrollment (OEP) | Oct 15 - Dec 7 | Change MA or Part D plans |
| MA Open Enrollment | Jan 1 - Mar 31 | Switch MA plans or return to Original Medicare |
| Medigap Open Enrollment | 6 months from 65 + Part B | Buy any Medigap policy guaranteed |