Initial Enrollment Period (IEP)
Your IEP is the 7-month window when you first become eligible for Medicare, typically around your 65th birthday. It begins 3 months before the month you turn 65, includes your birthday month, and ends 3 months after.
If you're already collecting Social Security at 65, you'll be enrolled in Parts A and B automatically. If not, you need to actively sign up at ssa.gov/medicare.
The IEP is also when you can first join a Medicare Advantage plan, a Part D plan, or buy a Medigap policy (Medigap has its own 6-month window, see below).
See our turning-65 guide for a full timeline of what to do during your IEP.
Annual Enrollment Period (AEP)
The AEP runs October 15 to December 7 every year. This is the main annual window for everyone on Medicare to make plan changes for the following calendar year. New coverage starts January 1.
During AEP, you can:
- Switch from Original Medicare to a Medicare Advantage plan (or vice versa)
- Switch from one Medicare Advantage plan to another
- Join, drop, or switch a Part D prescription drug plan
AEP is when carriers release their plan changes for the next year, new premiums, formulary updates, network changes. It's a good idea to review your current plan's Annual Notice of Change each fall, even if you don't plan to switch.
Medicare Advantage Open Enrollment Period (OEP)
The MA OEP runs January 1 to March 31 every year. It's only available to people who are already enrolled in a Medicare Advantage plan as of January 1.
During OEP you can make one change:
- Switch from one Medicare Advantage plan to another
- Drop your Medicare Advantage plan and return to Original Medicare (and add a stand-alone Part D plan)
You cannot use the MA OEP to switch from Original Medicare into a Medicare Advantage plan, that has to happen during AEP or a Special Enrollment Period.
General Enrollment Period (GEP)
The GEP runs January 1 to March 31 every year. It's a backstop for people who:
- Missed their Initial Enrollment Period, and
- Don't qualify for a Special Enrollment Period
Coverage for those enrolling during GEP starts the month after enrollment. If you're using the GEP because you missed your IEP without creditable coverage, you may owe a Part B late-enrollment penalty for the time you went without, added to your premium for as long as you have Medicare.
Special Enrollment Periods (SEPs)
SEPs let you make plan changes outside the normal windows when something qualifying happens. Common triggers:
- You lose other coverage (e.g., leaving a job with employer health insurance)
- You move to a new ZIP code with different plan options
- You qualify for Medicaid or for Extra Help with prescription costs
- You become eligible for a Medicare Savings Program
- You leave incarceration
- Your plan's contract with Medicare ends or its service area changes
- You're affected by a federally declared disaster
Each SEP has its own timing rules, usually 2-3 months from the qualifying event. A licensed agent can confirm whether your situation qualifies and help you act in time.
Medigap Open Enrollment Period
This is a one-time 6-month window that starts the first month you're both age 65 or older and enrolled in Part B. During this window, you can buy any Medigap policy sold in your state from any insurer at the same price as healthy enrollees, no medical underwriting, no denials.
This is hands-down the best time to buy Medigap. Outside this window , and outside specific guaranteed-issue Special Enrollment situations , insurers in most states can use medical underwriting, which can mean denial or higher premiums based on health.
See our Medigap guide for details on the lettered plans and how Medigap works.
Quick reference: every Medicare enrollment period
- IEP, 7 months around your 65th birthday
- AEP, October 15 to December 7 every year
- MA OEP, January 1 to March 31 every year (current MA enrollees only)
- GEP, January 1 to March 31 every year (backstop)
- Medigap Open Enrollment, 6 months starting the first month you're 65+ and on Part B
- SEP: varies by qualifying event