Key points
- The Initial Enrollment Period, or IEP, lasts 7 months around your 65th birthday month.
- AEP for 2027 is October 15 to December 7, 2026. Changes generally start January 1, 2027.
- The Medicare Advantage Open Enrollment Period is January 1 to March 31 for people already in Medicare Advantage. It allows one change.
- A Special Enrollment Period, or SEP, can follow events such as moving or losing employer coverage. Some people with full Medicaid can join an integrated D-SNP once each calendar month.
- The General Enrollment Period, or GEP, is January 1 to March 31 each year for certain late Part A or Part B sign-ups. Coverage starts the month after enrollment.
The calendar at a glance
Use this table as a starting point. Your exact effective date can depend on when Medicare or the plan receives your request.
| Period | When | What it can do | Typical effective date |
|---|---|---|---|
| IEP | 7 months around age 65 | Join Medicare and a plan | Depends on when you enroll |
| AEP | October 15 to December 7 | Change health or drug coverage | January 1 of the next year |
| Medicare Advantage OEP | January 1 to March 31 | One change if already in Medicare Advantage | First of the next month |
| SEP | Varies | Change coverage after a qualifying event | Depends on the event |
| GEP | January 1 to March 31 | Sign up for Part A or Part B if late | Month after enrollment |
IEP when you turn 65
Your IEP generally starts 3 months before the month you turn 65 and ends 3 months after that month. It is the main time to sign up for Part A and Part B and choose how to receive Medicare coverage.
If you sign up before your birthday month, Part B usually starts in your birthday month. If you sign up in your birthday month or in the following 3 months, Part B usually starts the next month. People born on the first day of a month can have different dates, so check with Social Security.
AEP and Medicare Advantage OEP
During AEP, you can make the 2027 changes allowed for your current coverage. The plan must receive the request by December 7 for the usual January 1 start.
During Medicare Advantage OEP, a person already in Medicare Advantage can switch to another Medicare Advantage plan or return to Original Medicare and join a separate drug plan. You can make one change. A person in Original Medicare cannot use this period to join Medicare Advantage.
SEPs after life changes
SEPs are available for situations such as moving, losing employer coverage, losing Medicaid, or getting Extra Help. The window and effective date depend on the event. A person who loses job-based coverage may have a 2-month plan SEP, while the Part B SEP after current employment is generally 8 months.
If you have Medicare and full Medicaid, Medicare.gov says you may be able to join or switch to an integrated D-SNP once each calendar month when one is available in your area. Not every D-SNP is integrated.
GEP and late penalties
The GEP runs January 1 to March 31. It is a late sign-up period for certain people who missed IEP or an SEP. Part B usually starts the month after you enroll.
Without a valid SEP, Part B can add 10% for each full 12-month period you were late, usually for as long as you have Part B. Part D can add 1% of the national base beneficiary premium for each month you go 63 days or more without creditable drug coverage. Extra Help generally removes the Part D penalty.
Steps
- Name your situation. Turning 65, still working, already in Medicare Advantage, moving, or losing coverage?
- Write down the last day. Do not wait for a reminder if your period has a fixed end date.
- Confirm the effective date. Ask Social Security or the plan when coverage begins.
- Keep proof. Save employer coverage letters, move records, Medicaid notices, and enrollment confirmations.
Quick check
- I know whether I am in IEP, AEP, OEP, SEP, or GEP.
- I know the date my request must be received.
- I checked whether a late penalty applies.
- I have asked Medicare or Social Security about my exact start date.
Questions to ask
- Which enrollment period applies to me?
- When will Part B or my new plan start?
- Do I need employer proof for an SEP?
- Will a late Part B or Part D penalty apply?
Common questions
What is IEP?
IEP is the 7-month Initial Enrollment Period around the month you turn 65. It is generally 3 months before, the birthday month, and 3 months after.
When is AEP for 2027?
AEP is October 15 to December 7, 2026. Changes generally take effect January 1, 2027.
Can I switch Medicare Advantage plans from January to March?
If you are already in Medicare Advantage, you can make one change during Medicare Advantage OEP from January 1 to March 31. You can switch to another Medicare Advantage plan or return to Original Medicare and join a drug plan.
Does moving create an SEP?
Usually, a move can create an SEP. The start and end dates depend on the move and whether the new address is in your plan's service area.
Does COBRA give me a Part B SEP?
No. Medicare says COBRA does not extend the limited time to sign up for Part B. Ask Social Security before coverage ends.
Can full Medicaid allow a monthly plan change?
You may be able to join or switch to an integrated D-SNP once each calendar month if one is available and you qualify. Confirm with Medicare.
Official sources
- Medicare.gov: Open Enrollment
- Medicare.gov: Joining a health or drug plan
- Medicare.gov: Special Enrollment Periods
- Medicare.gov: Avoid late enrollment penalties
- Medicare.gov: When does Medicare coverage start?
- California Department of Aging: HICAP Medicare counseling
Related guides
- Medicare 2027 in Orange County
- Medicare for green card holders working past 65
- Part D and Extra Help for 2027
- IRMAA and Medicare premiums
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