Medicare Enrollment Periods, Explained

The right Medicare enrollment period depends on what you need to change. Signing up for Part B, changing a Medicare Advantage plan, and buying Medigap follow different rules. Start with your current coverage and the coverage you want, then confirm both the application deadline and the start date.

For the coming plan year, Medicare's fall enrollment period runs October 15 through December 7, 2026, for 2027 plan choices. Changes generally start January 1, 2027; the plan must receive your enrollment request by December 7. CMS confirms the fall dates, and Medicare explains the effective date.

Match the enrollment window to the coverage

Original Medicare includes Part A, hospital insurance, and Part B, medical insurance. Medicare Advantage, or Part C, is an alternative way to receive those benefits. Part D covers prescription drugs through a separate drug plan or a health plan with drug coverage. Medicare's coverage overview distinguishes these choices.

Recurring window	What it allows	When the change starts
Annual Enrollment Period, October 15 to December 7	Join, switch, or drop Medicare Advantage or Part D; move between Advantage and Original Medicare	January 1 of the following year
Medicare Advantage Open Enrollment, January 1 to March 31	If already in Advantage, switch Advantage plans or return to Original Medicare, with the option to add Part D	First of the month after the plan receives your request
General Enrollment, January 1 to March 31	Sign up for Part B or Part A that requires a premium after missing initial enrollment, without a qualifying special period	Month after you sign up

Sources: Medicare's plan-change calendar and Part A and Part B enrollment rules. The two January windows serve different purposes.

New to Medicare: use your Initial Enrollment Period

For most people turning 65, the Initial Enrollment Period lasts seven months: three before your birthday month, the birthday month, and three after. If you enroll in Part B before your birthday month, coverage generally starts in your birthday month. Enroll during the birthday month or the following three months, and Part B starts the next month. Check Medicare's start-date rules if you qualify before 65.

If your birthday is on the first day of the month, your seven-month window shifts earlier: it starts four months before your birthday month and ends two months after. Enrolling during its first three months generally starts coverage the month before your birthday month. Medicare & You 2027, page 17, explains this exception.

You need both Part A and Part B for Medicare Advantage, but either Part A or Part B for a separate Part D plan. If you add Part B later while already having Part A, there is a separate initial opportunity to join Advantage, including two months after first getting both parts. Confirm the dates using Medicare's joining-a-plan guidance.

If you join Advantage during your Initial Enrollment Period, you can also switch Advantage plans or return to Original Medicare within the first three months you have both Part A and Part B. This opportunity is separate from the recurring January-to-March window. Medicare lists this initial plan-change right.

Fall and winter plan changes have different limits

The fall Annual Enrollment Period, often called AEP, is the broad yearly opportunity to change health and drug plans. It does not enroll you in Part B or erase an existing late enrollment penalty. Part B enrollment and penalties have their own rules. Review the plan windows alongside Medicare's penalty guidance.

The Medicare Advantage Open Enrollment Period allows one change between January 1 and March 31 if you are already in Advantage. It cannot be used to move from Original Medicare into Advantage or simply switch separate Part D plans while remaining in Original Medicare. A different initial or special enrollment right may apply. Medicare & You 2027, page 75, explains these limits.

Retiring: track Part B and drug coverage separately

Qualifying group health coverage based on your or your spouse's current employment can let you delay Part B. You can enroll while that employment and coverage continue. The employment-related Special Enrollment Period generally ends eight months after employment or that coverage ends, whichever happens first. COBRA does not extend this clock; losing COBRA or retiree coverage does not itself create this Part B enrollment right. This employment exception does not apply to eligibility based on End-Stage Renal Disease, or ESRD. Medicare lists the conditions.

Before delaying, ask your benefits administrator how the employer plan works with Medicare. At 65, coverage from an employer with fewer than 20 employees might not pay properly without Part A and Part B. Have Social Security or the Railroad Retirement Board receive your completed Part B forms the month before job coverage ends if you need Medicare to begin immediately afterward. Medicare's employer-coverage questions help identify these issues.

Drug coverage uses a different clock. Leaving employer or union coverage, including COBRA, generally gives you two full months after the month coverage ends to join an Advantage or drug plan. Do not use the eight-month Part B deadline for Part D. Check the applicable plan special period.

That plan-enrollment window is not a penalty-free waiting period. Confirm the new drug coverage's start date: a gap of 63 or more consecutive days without Part D or other creditable drug coverage after initial enrollment can trigger a penalty, even if an enrollment window remains open. Medicare explains the separate gap test.

Also request your creditable drug coverage notice. Creditable means the coverage is expected to pay, on average, at least as much as Part D. Maintaining creditable coverage can protect against the Part D penalty, even though it does not establish a Part B enrollment exception. Medicare explains creditable coverage.

Other special periods depend on the event

A move outside your plan's service area, a plan contract ending, or changes involving Medicaid or Extra Help with drug costs can create a Special Enrollment Period. The permitted changes and deadlines depend on the event. For example, notifying your plan before a move outside its service area opens a window the month before the move, continuing for two full months afterward. Find your situation in Medicare's special-period guidance.

Keep the notice that documents the event. Ask which enrollment right applies, what it allows, and when replacement coverage starts.

Keep Medigap purchase rights separate

Medigap, also called Medicare Supplement insurance, helps pay certain out-of-pocket costs in Original Medicare. It does not pay Medicare Advantage cost sharing. Medicare & You 2027, page 68, explains why it cannot cover Advantage costs.

Its federal six-month Open Enrollment Period starts the first month you are 65 or older and have Part B. It is a one-time window, not the annual fall period. Afterward, an insurer may use medical underwriting, a review of your health history, and deny an application unless a specific protection applies. State law may provide additional rights. Medicare explains these purchase protections.

Returning to Original Medicare during AEP or Advantage Open Enrollment does not automatically give you protected access to Medigap. Check your rights before changing coverage. Our Advantage versus Supplement guide explains the broader decision.

Check penalties before waiting

Medicare's late enrollment rules distinguish three penalties:

• Part B: Generally 10% of the standard Part B premium for each full 12-month period you could have enrolled but did not, usually for as long as you have Part B. Qualifying special periods and Medicare Savings Programs can provide exceptions.
• Part D: After initial enrollment, going 63 or more consecutive days without Part D or other creditable drug coverage can trigger a monthly penalty. It is 1% of the national base beneficiary premium per full uncovered month, generally while you have drug coverage. Extra Help provides an exception.
• Premium Part A: If you must buy Part A, late enrollment can increase the premium by 10%, generally for twice the years you delayed.

Write down your current coverage end date, enrollment deadline, and new start date. Bring your coverage notices and medication list to ask NavaQuote about your Medicare options. Use our Part D coverage guide to prepare the prescription comparison.