Your first chance is the Initial Enrollment Period, seven months around the month you turn 65. After that, the Open Enrollment Period runs from October 15 to December 7 each year, when you can join, drop or switch a Medicare Advantage or drug plan, with new coverage starting January 1. Special Enrollment Periods follow certain life events, and a Medigap policy has its own one-time window of six months.
The dates that repeat each year
General Enrollment Period
January 1 to March 31
Part A and Part B, if you missed your first chance
Medicare Advantage Open Enrollment Period
January 1 to March 31
Only if you are already in a Medicare Advantage Plan
Open Enrollment Period
October 15 to December 7
Medicare Advantage and drug plans; new coverage January 1
Your Initial Enrollment Period and any Special Enrollment Period depend on your own dates, so they don't fit on a yearly calendar.
Your first chance: the Initial Enrollment Period
It lasts seven months: it starts three months before the month you turn 65 and ends three months after that month. If you sign up for Part B before the month you turn 65, your coverage starts in your birthday month; if you sign up in your birthday month or the three months after, it starts the next month.
If you miss it and don't qualify for a Special Enrollment Period, your next chance for Part A and Part B is the General Enrollment Period, January 1 to March 31, with coverage starting the month after you sign up, and you might pay a late enrollment penalty.
Coming up on 65? The steps in order are on the turning 65 page.
Medicare.govEach fall: October 15 to December 7
This is Medicare's Open Enrollment Period. During it you can join, drop or switch to another Medicare Advantage Plan, with or without drug coverage; move from Original Medicare to a Medicare Advantage Plan or back; and join, drop or switch a Medicare drug plan if you have Original Medicare.
Opens
October 15
The plan must get your request by
December 7
New coverage starts
January 1
January to March, if you are in a Medicare Advantage Plan
There's a second period, and it's only for people already in a Medicare Advantage Plan. From January 1 to March 31, or within the first three months you have Medicare, you can change to another Medicare Advantage Plan, or leave yours for Original Medicare and join a separate Medicare drug plan. Coverage starts the first of the month after the plan gets your request.
If you have Original Medicare, this period doesn't apply to you.
Special Enrollment Periods
These open up after certain changes in your life, and each one has its own time limit. Here are a few of them:
Coverage from a current job
Yours or your spouse's: sign up for Part A and Part B any time you're covered, or within eight months after the work or the coverage ends, whichever happens first.
Moving
If you move out of your plan's service area, your chance to switch plans begins when you move and lasts two full months after.
Leaving job or union coverage
Including COBRA: you have two full months after the month it ends to join a Medicare Advantage Plan or a Medicare drug plan.
Losing creditable drug coverage
If you lose it through no choice of your own, you have two full months to join a plan with drug coverage.
Medicaid or Extra Help
If you have Medicaid or get Extra Help, you can change your drug coverage once a calendar month.
One to watch: COBRA or retiree coverage ending doesn't open a Special Enrollment Period for Part A and Part B.
Medicare.govThe Medigap Open Enrollment Period
A Medigap policy has its own one-time window: six months, starting the first month you have Part B and are 65 or older. During it you can buy any Medigap policy, and the insurance company can't deny you coverage because of health problems you already have. It doesn't repeat every year. After it, you may not be able to buy a Medigap policy, or it may cost more.
If you sign up for Part B while you still have coverage from a job, the six months start then.
Medicare.govWhat to compare in your yearly review
Each fall a Medicare Advantage or drug plan sends its members an Annual Notice of Change, with any changes in coverage and costs that take effect in January, and an Evidence of Coverage. When they arrive, hold them up against what you actually use:
- Your prescriptions: whether the plan still covers each one, and the yearly cost estimate for the drugs you take.
- Your doctors and pharmacies: whether each one is still in the plan's network.
- The costs: the monthly premium and the deductibles for next year.
- Where you spend the year: if you live in another state for part of it, whether the plan covers you there.
If nothing that matters to you has changed, keeping the plan you have is a perfectly normal outcome.
Questions people ask
What is the 3 month rule for Medicare?
Two Medicare rules involve three months. Your Initial Enrollment Period starts three months before the month you turn 65 and ends three months after that month. And if you join a Medicare Advantage Plan when you first get Medicare, you can change to another Medicare Advantage Plan, or go back to Original Medicare, within the first three months you have Part A and Part B. Source: Medicare.gov, 2026.
How long is the enrollment period for Medicare?
It depends on the period. The Initial Enrollment Period lasts seven months. The Open Enrollment Period runs from October 15 to December 7 each year. The General Enrollment Period and the Medicare Advantage Open Enrollment Period both run from January 1 to March 31. The Medigap Open Enrollment Period lasts six months, and the Special Enrollment Period for job coverage lasts until eight months after the work or the coverage ends, whichever happens first. Source: Medicare.gov, 2026.
What triggers a Special Enrollment Period for Medicare?
Certain events in your life. For Part A and Part B, the main one is coverage from your own or your spouse's current job: you can sign up while you are covered, or within eight months after the work or the coverage ends, whichever happens first. For Medicare Advantage and drug plans, events such as moving, losing other coverage, getting Medicaid or getting Extra Help open one. COBRA or retiree coverage ending does not open one for Part A and Part B. Source: Medicare.gov, 2026.
Do I need to re-enroll in Medicare Part B every year?
No. You pay the Part B premium each month, and keeping Part B is your choice; there's no yearly sign-up for it. What can change each year is a plan you join: each fall a Medicare Advantage or drug plan sends an Annual Notice of Change with any changes for January, and a Medigap policy renews automatically every year as long as you pay its premium. Source: Medicare.gov, 2026.
More guides like this one are on the Learn page.