Every Window Explained · NPN #22255420
Medicare Enrollment Periods
Medicare has five enrollment windows, and they're easy to confuse — two of them even run on the same dates while doing completely different things. Here's what each one is, who it's for, and what happens if you miss it.
Reviewed by Philip Smith, Licensed Insurance AgentNPN #22255420FL Lic. #G349232Updated July 2026
Quick Answer
What are the Medicare enrollment periods?
There are five. Your Initial Enrollment Period is the 7 months around your 65th birthday. The Annual Enrollment Period runs October 15 to December 7 for Advantage and Part D changes. The Medicare Advantage Open Enrollment Period (January 1 to March 31) allows one plan change if you're already in an Advantage plan. The General Enrollment Period (January 1 to March 31) is the fallback if you missed your IEP. Special Enrollment Periods open after qualifying life events.
All Five Windows at a Glance
Note that the Advantage OEP and the General Enrollment Period share the same dates but serve entirely different people.
| Period | When | Who it's for | What you can do |
|---|---|---|---|
| IEP — Initial | 7 months around your 65th birthday | Anyone turning 65 | Enroll in Part A, Part B, Advantage, or Part D for the first time |
| AEP — Annual | Oct 15 – Dec 7 | Everyone on Medicare | Join, switch, or drop Advantage and Part D; effective Jan 1 |
| MA OEP | Jan 1 – Mar 31 | Only those already in an Advantage plan | One change: switch Advantage plans or return to Original Medicare |
| GEP — General | Jan 1 – Mar 31 | Missed IEP, no SEP available | Sign up for Part A and/or Part B; coverage starts the month after you enroll |
| SEP — Special | Varies by event | Anyone with a qualifying life change | Enroll or change plans outside the normal windows |
The July 1 rule is out of date
A lot of Medicare guidance still says that if you enroll during the General Enrollment Period, your coverage won't start until July 1. That hasn't been true since 2023. Coverage now begins the first day of the month afteryou enroll — so signing up in January means coverage on February 1, not a five-month wait. If someone is telling you otherwise, they're working from old information.
The Three You're Most Likely to Use
Initial Enrollment Period (IEP)
Your one-time, 7-month window built around your 65th birthday: the 3 months before your birthday month, the birthday month itself, and the 3 months after. Enrolling in the first three months generally gets coverage started soonest.
Annual Enrollment Period (AEP)
October 15 to December 7 every year. This is when anyone on Medicare can join, switch, or drop a Medicare Advantage or Part D plan. Changes you make take effect January 1 of the following year.
Special Enrollment Period (SEP)
Triggered by life events rather than the calendar — losing job-based coverage, moving out of your plan's service area, qualifying for Medicaid or Extra Help, or entering a nursing facility. Each trigger has its own window and rules.
Late enrollment penalties are permanent
The Part B penalty adds 10% to your premium for every full 12 months you could have enrolled and didn't — and it stays on your premium for as long as you have Part B. Part D carries its own separate penalty. If you're still working past 65 with employer coverage, different rules apply and you may be fine; the mistake is assuming that without checking. See our full enrollment guide for the penalty details.
Enrollment Period FAQs
When is my Medicare Initial Enrollment Period?
It runs for seven months centered on your 65th birthday: the three months before your birthday month, your birthday month, and the three months after. If you enroll during the three months before you turn 65, coverage generally begins the first day of your birthday month. Enrolling later in the window pushes your start date back, which is why signing up early in the period is usually the safer choice.
What is the difference between AEP and the Medicare Advantage Open Enrollment Period?
AEP runs October 15 to December 7 and is open to everyone on Medicare — you can join, switch, or drop Medicare Advantage and Part D plans, with changes effective January 1. The Medicare Advantage Open Enrollment Period runs January 1 to March 31 and is narrower: it is only for people already enrolled in a Medicare Advantage plan, and it allows one change — switch to a different Advantage plan or go back to Original Medicare. You cannot use the Advantage OEP to join an Advantage plan from Original Medicare.
When does coverage start if I use the General Enrollment Period?
Coverage now begins the first day of the month after you enroll. The General Enrollment Period runs January 1 to March 31 and is for people who missed their Initial Enrollment Period and don't qualify for a Special Enrollment Period. This is an important update: before 2023, General Enrollment Period coverage did not start until July 1 regardless of when you signed up, and a lot of older guidance online still says that. Under the current rules, enrolling in January means coverage starting February 1.
What qualifies me for a Medicare Special Enrollment Period?
Common triggers include losing employer or union coverage, moving to a new address outside your plan's service area, becoming eligible for Medicaid or the Extra Help program, moving into or out of a skilled nursing facility, and your plan leaving the Medicare program. Each has its own timeline — often around two months from the qualifying event, though the specifics vary. If you think a life change may have opened a window for you, it's worth confirming quickly, since these periods close.
What happens if I miss my Medicare enrollment window?
You may face a permanent late enrollment penalty and a wait for coverage. The Part B penalty adds 10% to your premium for each full 12-month period you could have had Part B but didn't, and it generally lasts as long as you have Part B. Part D has its own separate penalty. If you missed your Initial Enrollment Period and have no qualifying Special Enrollment Period, the General Enrollment Period (January 1 to March 31) is typically your next opportunity.
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