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Medicare Part C Enrollment Period: Every Window, Who Qualifies and What Each One Allows

Reviewed by Russell Noga, Licensed Medicare Insurance Broker (all 50 states) — Last updated November 6, 2026

There is no single Medicare Part C enrollment period: you can join a Medicare Advantage plan in your 7-month Initial Enrollment Period, every fall from October 15 to December 7, or during a Special Enrollment Period, and current members get one extra change from January 1 to March 31. For 2027 coverage, the fall window runs October 15 through December 7, 2026.

2027 by the Numbers

7 months

length of the Initial Enrollment Period around your 65th birthday month (Medicare.gov)

Oct 15-Dec 7

2026 fall window for plans that start January 1, 2027 (CMS)

Jan 1-Mar 31

2027 window for one change by current Part C members (CMS)

Part C is the official name for Medicare Advantage, the private plans that replace Original Medicare for hospital and doctor coverage. Medicare controls when people may join, leave or trade these plans, and it does so through a handful of separate windows, each with its own audience and its own limits.

This page works as a reference map. It names every window, explains who can use it and shows what each one does and does not allow. If you are still lining up Parts A and B, start with the guide on when to enroll in Medicare, because Part C enrollment depends on having both.

✔ Licensed in all 50 states
✔ Based on CMS 2027 data
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Key Highlights

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You need Part A and Part B, and you must live in the plan’s service area, before any Part C window helps you.

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The Initial Coverage Election Period matters most to people who delayed Part B past 65.

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The fall window is open to everyone with Medicare; the January to March window is only for people already in a plan.

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Special Enrollment Periods are tied to events such as a move or a change in Medicaid, not to the calendar.

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The Part C Windows Side by Side

Window Who can use it When it runs What it allows Coverage begins
Initial Enrollment Period (IEP) People turning 65 3 months before the birthday month, that month, and 3 months after Join a Part C plan with or without drug coverage Depends on when you sign up within the window
Initial Coverage Election Period (ICEP) People getting Part B later, or under 65 with a disability Starts 3 months before you have both Part A and Part B First chance to join a Part C plan When Part A and Part B are both in place, or the month after
Fall open enrollment Anyone with Medicare October 15 to December 7 each year Join, switch or drop a Part C plan January 1
Medicare Advantage Open Enrollment People already in a Part C plan January 1 to March 31, or the first 3 months of a new member’s coverage One switch, or a return to Original Medicare First of the month after the request
Special Enrollment Periods People with a qualifying event Varies by event Varies by event Usually the first of the next month

Based on Medicare.gov and CMS enrollment rules in effect for 2027 coverage.

Two conditions sit under every row. You must have Part A and Part B, and you must live in the area the plan serves. Without both, no window opens for you.

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Your First Opening: The IEP and the ICEP

For most people, the first chance to join Part C is the Initial Enrollment Period. It is seven months long and centers on the month you turn 65. Medicare coverage itself begins on the first day of your birthday month, or the month before if your birthday falls on the 1st.

1

Example birthday: July 14, 2027 The window opens April 1, 2027 and closes October 31, 2027.

2

Sign up April through June A plan chosen before the birthday month generally starts July 1, the same day Medicare does.

3

Sign up in July or later Coverage generally starts the first of the month after the plan receives the application.

4

Waiting until fall Missing the seven months does not end your options, but it pushes you to the October 15 window or a qualifying event.

Who the ICEP is for: The Initial Coverage Election Period exists for people whose Part B start date does not line up with age 65, such as someone who kept employer coverage and enrolled in Part B at 67. It opens three months before both parts are in force and closes on the later of two dates: the last day of the month before both parts start, or the end of the Part B Initial Enrollment Period. For many 65-year-olds it overlaps the IEP completely.

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The October 15 to December 7 Window

Allowed during the 2026 fall window, for coverage on January 1, 2027

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Join a Part C plan for the first time after starting on Original Medicare.

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Move from one Part C plan to another, including between HMO and PPO plans.

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Leave Part C and go back to Original Medicare, with or without a standalone Part D plan.

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Add or drop drug coverage inside a Part C plan by choosing a plan that includes it or one that does not.

Applications can be changed during the window, and the final one received by December 7 is the one Medicare uses. Drug plan rules follow the same calendar; the page on Part D enrollment periods covers the drug-only side. The exact 2027 cycle, from plan notices in September to deadlines next fall, is laid out on the 2027 Medicare Advantage enrollment calendar.

January 1 to March 31: A Second Look for Members

Possible in this window

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Trade your current Part C plan for a different one

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Drop Part C, return to Original Medicare and add a Part D plan

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New members: one change within the first 3 months of coverage

Not possible in this window

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Joining Part C from Original Medicare

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A second change after the first one is made

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Switching only a standalone drug plan while on Original Medicare

A change made in this window takes effect the first day of the following month. A request in February 2027, for example, starts March 1, 2027.

Special Enrollment Periods: Event-Based Openings

Qualifying event How long the opening lasts
Moving out of the plan’s service area From the month before the move, if the plan is told in advance, through 2 full months after
Losing Medicaid eligibility 3 full months from losing eligibility or being notified, whichever is later
Full Medicaid or Extra Help Once per calendar month, for specific changes only
Plan leaving Medicare for next year December 8 through the last day of February
Switching to a 5-star rated plan Once between December 8 and November 30
Moving into or out of a nursing home While living there and 2 full months after leaving
Losing employer or union coverage 2 full months after the coverage ends

Timing from Medicare.gov’s Special Enrollment Period listings. Some events allow only certain kinds of changes.

People with both Medicare and full Medicaid may also qualify for dual special needs plans, which have their own rules; see what a special needs Medicare Advantage plan is.

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Our Analysis of CMS 2027 Plan Data: How Much Choice Each Window Unlocks

An enrollment window only matters if there is something to choose. The CMS 2027 plan and county files show how uneven that choice is from one county to the next.

40

median number of individual Part C plans available per county for 2027

7

median number of insurer brands offering plans in a county

230

counties with 5 or fewer individual plans

156

counties served by only one insurer brand

Source: Our analysis of CMS 2027 plan data, counting individual plans only (employer group, PACE and cost plans excluded). Plan benefits for 2027 vary by plan and area, and not every plan offers every extra.

If a Window Closes Before You Act

Part B comes first: Someone who skipped Part B at 65 without other qualifying coverage generally waits for the General Enrollment Period, January 1 to March 31, and may owe a lasting Part B late penalty. Joining a Part C plan after that sign-up is a separate step that depends on Medicare’s rules at the time.

Typical paths after a missed window

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Missed the IEP but have Parts A and B: wait for October 15, unless an event qualifies you sooner.

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Missed December 7 while already in a plan: use the January to March window for one change.

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Missed December 7 while on Original Medicare: the next routine chance is the following October.

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Plan leaving your area: the special window runs into late February, so there is time after the fall deadline.

Mechanics of trading one plan for another, including what happens to drug coverage, are covered on can I switch Medicare Advantage plans.

Bottom Line

The Bottom Line

Part C enrollment runs on several clocks at once: a personal first window around age 65 or Part B, an annual fall window for everyone, a January to March window for members, and event-based openings in between. Knowing which clock applies to you tells you both when you can act and when the new plan will start.

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Frequently Asked Questions

➤ Is the Medicare Part C enrollment period the same as Part D’s?

The fall window is shared, October 15 to December 7, and the life-event openings are largely the same. The January to March window differs: it is for Part C members, and drug plan changes in that window are tied to leaving or switching Part C.

➤ Do I need Part B to join a Part C plan?

Yes. Medicare requires both Part A and Part B, and you keep paying the Part B premium while in a Part C plan, along with any premium the plan charges.

➤ What does ICEP stand for?

Initial Coverage Election Period. It is the first window to join a Part C plan, built around the date both Part A and Part B take effect, which matters most to people who started Part B after 65.

➤ Can I join a Part C plan at 66 if I skipped it at 65?

Yes, if you have Parts A and B. You would use the October 15 to December 7 window for a January 1 start, or a Special Enrollment Period if an event such as a move applies.

➤ How many times can I change plans in the fall window?

As many applications as you like can be submitted between October 15 and December 7, but only the last one received by the deadline takes effect on January 1.

➤ Does the January to March window let me join Part C from Original Medicare?

No. It is limited to people already enrolled in a Part C plan, who can switch once or go back to Original Medicare.

➤ Can people under 65 use a Part C enrollment period?

Yes. People with Medicare due to a disability have an initial window tied to their Medicare start, and people with end-stage renal disease may join Part C plans as well.

➤ Will the plan I pick in December start right away?

No. Plans chosen during the October 15 to December 7 window all start January 1 of the next year, so a choice made for 2027 begins January 1, 2027.

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