When you can enroll in Medicare — every enrollment period explained.
Medicare uses several enrollment windows. Missing the right one can mean late penalties or waiting up to a full year to make a change. Here’s what each one covers.
Initial Enrollment Period (IEP)
A 7-month window built around your 65th birthday: the 3 months before, the month of, and the 3 months after. This is when most people first sign up for Part A and Part B. If you don't enroll during your IEP and don't have other qualifying coverage, late enrollment penalties may apply for the rest of your life.
Annual Enrollment Period (AEP)
October 15 through December 7 every year. The big one. During AEP you can switch from Original Medicare to a Medicare Advantage plan or vice versa, switch between Medicare Advantage plans, switch Part D drug plans, or drop or add Part D. Changes take effect January 1.
Medicare Advantage Open Enrollment Period (MA-OEP)
January 1 through March 31 every year. If you're already enrolled in a Medicare Advantage plan, you have one chance during this window to switch to a different Medicare Advantage plan, or drop your Medicare Advantage plan and return to Original Medicare (and add a Part D plan if you want). You cannot switch into a Medicare Advantage plan during MA-OEP if you're currently on Original Medicare.
General Enrollment Period (GEP)
January 1 through March 31 every year. For people who missed their IEP and don't qualify for a Special Enrollment Period. Coverage starts the month after you enroll.
Special Enrollment Periods (SEPs)
Triggered by specific life events: moving to a new service area, losing employer coverage, qualifying for Extra Help, becoming dual-eligible for Medicaid, and others. Each SEP has its own length and rules.
5-Star Special Enrollment Period
You can switch to a Medicare Advantage or Part D plan rated 5 stars by Medicare once between December 8 and November 30 of the following year, even outside other enrollment windows.
Medicare Supplement (Medigap) enrollment
Medigap has its own rules separate from Parts C and D. Your Medigap Open Enrollment Period is the 6-month window starting the month you turn 65 and are enrolled in Part B. During this window, insurers can't deny you coverage or charge you more based on your health. After this window, guaranteed-issue rights are limited and depend on the state and the situation. Some states (including New York and others) have additional state-level guaranteed-issue rules.
Plan year 2027 calendar
- AEP for plan year 2027: Oct 15 – Dec 7, 2026
- Plan year 2027 coverage begins: Jan 1, 2027
- MA-OEP / GEP for 2027: Jan 1 – Mar 31, 2027
- AEP for plan year 2028: Oct 15 – Dec 7, 2027
Late enrollment penalties
Missing your IEP without other qualifying coverage can mean:
- Part B penalty: 10% per 12-month period you delayed, added to your premium for life.
- Part D penalty: roughly 1% of the national base premium per uncovered month, added for life.
A licensed agent can help you check whether late penalties apply and whether your situation qualifies for an SEP.
Not sure which window you’re in?