What Are the 3 Enrollment Periods for Medicare? Complete Timeline

Medicare enrollment periods determine when you can sign up for Medicare for the first time, switch between plans, or change your coverage. The system isn't intuitive because Medicare has multiple enrollment windows with different rules, eligibility requirements, and consequences. Missing the right window can mean delayed coverage, late enrollment penalties that last a lifetime, or being stuck with a plan that doesn't fit your needs. Most Medicare guides describe three main enrollment periods (Initial, Annual, and Special), but the complete system actually includes seven distinct windows that beneficiaries need to understand. The Annual Enrollment Period for 2026 ran from October 15 to December 7, 2025, with changes taking effect January 1, 2026. The next AEP runs October 15 to December 7, 2026, for 2027 coverage. The Medicare Advantage Open Enrollment Period for 2026 runs from January 1 to March 31, 2026.

This guide explains each Medicare enrollment period for 2026, what you can do during each window, who qualifies, and how to avoid the most common enrollment mistakes. Information comes from Medicare.gov, CMS, and SHIP counseling resources.

The Initial Enrollment Period (IEP) for first-time enrollees

The Initial Enrollment Period is the most important enrollment window for people new to Medicare. It's a 7-month window centered on the month you turn 65, starting 3 months before your 65th birthday month, including your birthday month, and continuing 3 months after. For example, if you turn 65 in June 2026, your IEP runs from March 1 through September 30, 2026.

When you enroll during the IEP affects when your coverage starts. Enrolling during the first three months means coverage starts on the first day of your birthday month. Enrolling during your birthday month means coverage starts the first day of the following month. Enrolling during the last three months delays coverage start by one to three months. The practical implication is significant: enroll during the first three months of your IEP to ensure coverage starts on the first day of your birthday month, avoiding any coverage gaps.

You're typically auto-enrolled in Medicare Parts A and B if you're already receiving Social Security or Railroad Retirement benefits when you turn 65. If you're not receiving these benefits, you need to actively enroll through SSA at ssa.gov/medicare or by calling 1-800-772-1213.

The IEP is also your initial 6-month Medigap Open Enrollment Period when you can purchase any Medicare Supplement plan without medical underwriting. This guaranteed-issue window starts the month you turn 65 and enroll in Part B, and most states never offer guaranteed-issue Medigap rights again outside this window. For comprehensive enrollment guidance, see our Medicare basics guide.

The Annual Enrollment Period (AEP) for existing beneficiaries

The Annual Enrollment Period (AEP), also called the Medicare Annual Election Period or Medicare Open Enrollment Period, is the primary annual window when existing Medicare beneficiaries can review and change their coverage. The AEP runs from October 15 to December 7 every year, with changes taking effect January 1 of the following year.

During the AEP, you can switch from Original Medicare to Medicare Advantage, switch from Medicare Advantage back to Original Medicare, change from one Medicare Advantage plan to another, enroll in or change Medicare Part D prescription drug plans, or drop existing Medicare Advantage or Part D coverage entirely.

The AEP does not provide guaranteed-issue rights for Medicare Supplement plans. You can apply for Medigap during the AEP, but most state insurers will medically underwrite you, charge higher premiums for pre-existing conditions, or deny coverage if you're outside your initial 6-month Medigap Open Enrollment Period. The exceptions are Connecticut, Massachusetts, Maine, and New York where insurers must offer at least one Medigap policy without medical underwriting, plus 16+ "birthday rule" states that offer limited annual guaranteed-issue access.

Two weeks before the AEP begins each year (around October 1), insurance carriers release their plan information for the following year. By September 30 each year, your current plan mails you an Annual Notice of Change (ANOC) detailing any cost, benefit, or network changes for the coming year. The ANOC is critical reading because plans frequently change cost-sharing, drug formularies, and provider networks. If your current plan no longer fits your needs, the AEP is when to switch.

The Medicare Advantage Open Enrollment Period (MA OEP)

The Medicare Advantage Open Enrollment Period runs from January 1 to March 31 each year. This window is specifically for people already enrolled in Medicare Advantage who want to change plans or return to Original Medicare.

During the MA OEP, current Medicare Advantage enrollees can switch to a different Medicare Advantage plan (with or without drug coverage), or return to Original Medicare and add a standalone Part D plan if needed. Each beneficiary can make only one change during this window, and the change takes effect the first of the month after enrollment.

The MA OEP is more limited than the AEP. People in Original Medicare cannot use the MA OEP to switch to Medicare Advantage. People who switch from Medicare Advantage back to Original Medicare during the MA OEP may not qualify for guaranteed-issue Medigap rights unless other specific circumstances apply.

A common scenario where the MA OEP helps: a beneficiary who enrolled in a Medicare Advantage plan during the AEP and then discovered after January 1 that the plan didn't work as expected (perhaps a doctor isn't actually in-network, or the drug formulary doesn't cover medications well) can use the MA OEP to switch.

Special Enrollment Periods (SEPs) for qualifying life events

Special Enrollment Periods allow plan changes outside the standard enrollment windows when specific qualifying events occur. Common qualifying events include moving to a new area with different plan options, losing other creditable coverage (such as employer health insurance), qualifying for Medicaid or Extra Help, moving into or out of a long-term care facility, or your current plan terminating or significantly changing its provider network.

SEPs typically last 60 days, though some last longer depending on the triggering event. The change takes effect the first of the month after enrollment in most cases.

A new SEP specifically for 2026 affects Medicare Advantage enrollees who relied on the Medicare Plan Finder when choosing their plan. If you discover within the first three months of your new plan year that the provider information in Plan Finder was wrong and your doctors aren't actually in-network, you qualify for an SEP to switch plans or return to Original Medicare. This SEP runs for three months after the effective date of your plan and is unique to the 2026 plan year.

Another important SEP applies when a Medicare Advantage plan exits your market or significantly changes its provider network. With 2.9 million Medicare Advantage enrollees facing forced disenrollment in 2026 due to plan exits, this SEP is particularly relevant. Affected members typically receive notification from the plan and Medicare with specific dates for their SEP.

The 5-Star Special Enrollment Period runs annually from December 8 to November 30. During this window, beneficiaries can join or switch to a 5-Star Medicare Advantage plan or 5-Star Part D plan available in their area. Each beneficiary can use this enrollment opportunity only once per year. The 5-Star SEP exists to allow movement to top-quality plans regardless of the standard enrollment calendar.

The General Enrollment Period (GEP) and other windows

The General Enrollment Period runs from January 1 to March 31 each year. The GEP is for people who didn't enroll in Medicare during their Initial Enrollment Period and don't qualify for a Special Enrollment Period. Anyone enrolling during the GEP typically faces late enrollment penalties for both Part A (if they have to pay premiums) and Part B that apply for as long as they have Medicare.

Since 2023, coverage from GEP enrollment starts the first of the month after enrollment, not July 1 as it did in prior years. This change means someone enrolling on February 15 has coverage starting March 1. People who enroll during the GEP can also add Part D coverage or join a Medicare Advantage plan during the same window.

The Medigap Open Enrollment Period is separate from all Medicare-administered windows. This 6-month period starts when you turn 65 and enroll in Medicare Part B. During this window only, Medigap insurers must offer you any plan available without medical underwriting regardless of your health status. Missing this window means most state insurers can charge more or deny coverage based on health conditions.

For the 4 expansion states and 16+ birthday rule states, additional Medigap guaranteed-issue windows exist throughout the year.