Medicare Enrollment Periods Explained: The Complete 2026 Guide

This article is for general educational purposes only and is not insurance or medical advice. We are not affiliated with the U.S. government or Medicare. For official information, visit Medicare.gov or call 1-800-MEDICARE. See our Medical & Financial Disclaimer for details.

Medicare doesn’t let you sign up or switch plans whenever you want. Instead, there are several distinct windows, each with its own rules, deadlines, and — critically — consequences for missing them, including penalties that can follow you for life. Mixing these windows up is one of the most common and costly mistakes people make with Medicare. Here’s every enrollment period laid out side by side, with the coverage start dates that actually apply in 2026 rather than the ones most websites are still repeating.

The Quick Answer

Medicare has seven enrollment windows. Most people will only ever use two of them.

Period	When	Who it’s for
Initial Enrollment Period (IEP)	7 months around your 65th birthday	First-time Medicare enrollment
Annual Enrollment Period (AEP)	October 15 – December 7	Anyone with Medicare, for plan changes
Medicare Advantage Open Enrollment Period (MA OEP)	January 1 – March 31	People already in a Medicare Advantage plan, one change only
General Enrollment Period (GEP)	January 1 – March 31	People who missed their IEP
Special Enrollment Period (SEP)	Triggered by life events	Anyone with a qualifying circumstance
Medigap Open Enrollment Period	One-time, 6 months after enrolling in Part B at 65+	Guaranteed-issue Medigap access
5-Star Special Enrollment Period	December 8 – November 30	Anyone with a 5-star plan available locally, once per year

Most people will only ever need the IEP and the AEP. The others exist as safety nets or apply to more specific situations.

Initial Enrollment Period (IEP)

Your most important enrollment window, and the one nearly everyone encounters. It’s a personal 7-month period centered on your 65th birthday:

• The 3 months before your birthday month
• Your birthday month itself
• The 3 months after your birthday month

Timing inside this window changes your start date. Sign up during the 3 months before your birthday month and your coverage begins the month you turn 65. Sign up during your birthday month or in any of the 3 months after, and coverage begins the first day of the following month. Those are the rules published by Medicare on when Medicare coverage starts.

So the practical difference between signing up early and signing up late inside your own IEP is now one month, not several. Signing up in the first three months is still the cleanest option, because it’s the only one where your coverage and your 65th birthday line up exactly.

This is when you enroll in Part A and Part B, and typically when you’d also choose between Original Medicare (plus Part D and possibly Medigap) or a Medicare Advantage plan.

Annual Enrollment Period (AEP)

Runs October 15 – December 7 every year, open to anyone already on Medicare. During AEP you can:

• Switch between Original Medicare and Medicare Advantage in either direction
• Switch from one Medicare Advantage plan to a different one
• Join, switch, or drop a standalone Part D drug plan

Changes take effect January 1 of the following year, and Medicare is specific about the deadline: the plan has to receive your enrollment request by December 7, not merely have it postmarked. That detail, and the full list of what you’re allowed to change, is set out on Medicare’s page on joining a plan. See our full AEP deadline guide for a deeper dive on preparing for this specific window.

Medicare Advantage Open Enrollment Period (MA OEP)

Runs January 1 – March 31, but only for people already enrolled in a Medicare Advantage plan as of January 1. It allows just one change:

• Switch to a different Medicare Advantage plan, or
• Drop Medicare Advantage and return to Original Medicare (adding a standalone Part D plan if desired)

Unlike AEP changes, which all wait for January 1, a change made here takes effect the first of the month after your new plan receives the request.

A lesser-known variant: if you joined a Medicare Advantage plan as soon as you became eligible, your MA OEP isn’t the January–March calendar window at all. Medicare’s own guide to Medicare Advantage and drug plan enrollment periods defines it as running from the first month you have both Part A and Part B until the last day of the third month you have both. So if your Part A and Part B both start in March, your personal window to make one change runs March through the end of May.

General Enrollment Period (GEP)

Runs January 1 – March 31, and exists as a fallback for people who missed their Initial Enrollment Period and don’t qualify for a Special Enrollment Period. Two things to know about it:

• Your coverage starts the month after you sign up. Enroll in January, you’re covered on February 1. Enroll in March, you’re covered on April 1. Medicare states this directly on its page on when coverage starts. This is not the rule most websites will tell you — see the next section.
• Late enrollment penalties usually apply. For Part B, that’s a 10% surcharge added to your premium for each full 12-month period you were eligible but didn’t sign up, and it generally lasts as long as you have Part B. Two full years late means a 20% surcharge for life. Part D works differently: 1% of the national base beneficiary premium for each month you went without creditable drug coverage. Both are set out on Medicare’s page on avoiding late enrollment penalties.

The GEP is a genuine safety net, but it’s meant to be a last resort, not a plan. The penalty, not the waiting period, is what makes it expensive.

The July 1 Rule That No Longer Exists

Search for the General Enrollment Period and you will find page after page — including pages updated this year — telling you that GEP coverage doesn’t begin until July 1, no matter when you enrolled. Under that rule, signing up on January 2 meant waiting almost six months, uninsured, before Medicare paid for anything.

That rule was real, and it was punishing. It also stopped applying on January 1, 2023. CMS changed the effective date so that coverage begins the month after enrollment for anyone signing up in the GEP, or in the last three months of their IEP. The change is documented in the CMS fact sheet on implementing the Consolidated Appropriations Act, 2021 Medicare enrollment provisions, which describes both the old July 1 rule and the change that replaced it.

The difference is not academic. Someone who missed their IEP and signs up this coming January is covered on February 1 — not July 1. That’s five months of the difference between having health coverage and not having it, based on a rule that changed three years ago.

It’s also a useful test for any Medicare page you read, including this one. If a site still says July 1, it was either written before 2023 or copied from something that was. It’s worth asking what else on that page hasn’t been checked since.

Special Enrollment Periods (SEPs)

Triggered by specific qualifying life events, available whenever they apply rather than on a fixed calendar. Medicare’s page on Special Enrollment Periods lists the common triggers:

• Moving outside your plan’s service area
• Losing employer-based or other creditable coverage
• Moving into or out of an institution, such as a nursing home
• Being released from incarceration
• Returning to the U.S. after living abroad
• A declared natural disaster or emergency affecting your area

The eight-month trap: two different SEPs, two different clocks

This is where people who worked past 65 get caught, and it’s rarely explained clearly.

If you delayed Part B because you had job-based coverage, Medicare gives you an 8-month Special Enrollment Period once you stop working or lose that coverage, whichever happens first, to sign up for Part A and Part B without a penalty. Medicare confirms the eight months on its page about working past 65.

But the window for joining a plan — a Medicare Advantage plan or a standalone Part D drug plan — is much shorter. Medicare’s own wording is that your chance to join lasts for 2 full months after the month your coverage ends. That same two-month clock applies to most of the other life events above: moving back to the U.S., leaving an institution, being released from jail.

If this is your situation, treat the shorter clock as the real one and settle drug coverage first; the eight months only ever applied to Part B. Our article on what happens if you miss a Medicare deadline works the calendar through month by month and prices the penalty that follows.

Medigap Open Enrollment Period

A one-time, 6-month window that, in Medicare’s words, starts the first day of the month you’re 65 or older and signed up for Part B — both conditions, not either one. That’s set out on Medicare’s page on when to buy a Medigap policy.

What makes this window matter is what it protects. During those six months you can buy any Medigap policy sold in your state even if you have health problems, according to Medicare’s guide to buying a Medigap policy. Once it closes, that protection goes with it: the same page states that insurance companies don’t have to sell you a Medigap policy afterward unless you qualify for specific guaranteed issue rights. In practice that means medical underwriting in most states, though a handful of states give residents broader rights than federal law requires.

This window is separate from every Medicare Advantage period above, it runs on its own clock, and unlike the others it does not come back around next year.

The 5-Star Special Enrollment Period

An extra, lesser-known window: if a Medicare Advantage plan rated 5 stars is available where you live, you can switch into it once between December 8 and November 30 of the following year — outside all the standard windows described above. Medicare sets out the dates and the once-per-period limit on its Special Enrollment Periods page.

Worth checking before you assume it applies: 5-star plans are not available in every county, and in many areas there are none at all.

What Happens If You Miss a Window

The consequences vary significantly by which window you miss:

• Missing AEP: your current coverage generally rolls over automatically. You’ll likely wait for the next AEP unless a SEP applies. No penalty, but you’re locked into a plan you may have wanted to leave.
• Missing your IEP: you’ll need the GEP. Coverage starts the month after you enroll, but the Part B late enrollment penalty attaches and generally stays for life, and Part D’s penalty applies too if you went without creditable drug coverage.
• Missing your Medigap OEP: the most permanent of the three. You lose a one-time right that never returns, and in most states future Medigap applications can be underwritten or declined outright.

Frequently Asked Questions

Which enrollment period will I actually need to use most? For most people, it’s the IEP once, when you first become eligible, and then the AEP each fall afterward if you want to make changes. The other windows are safety nets for specific situations.

Do I need to re-enroll in Medicare every year? No. Once enrolled, your coverage renews automatically each year. You only need to take action during AEP if you specifically want to change something.

I read that General Enrollment Period coverage doesn’t start until July 1. Is that right? Not anymore. That was the rule until January 1, 2023. Coverage now starts the first day of the month after you sign up. A lot of websites, and a lot of well-meaning advice, still repeat the old July 1 rule.

What’s the real cost of missing my Initial Enrollment Period? The waiting period is short — coverage starts the month after you sign up during the GEP. The lasting cost is the Part B late enrollment penalty: a 10% premium surcharge for each full 12-month period you were eligible but didn’t enroll, added to your premium for as long as you have Part B.

Can I use a Special Enrollment Period any time? Only if you have a genuine qualifying life event — moving, losing other coverage, and similar circumstances. You can’t create a SEP simply because you changed your mind about your current plan outside the standard windows.

Is the Medigap Open Enrollment Period the same as the Medicare Advantage AEP? No — they’re completely separate. The Medigap OEP is a one-time, personal 6-month window tied to when you first have both Part B and your 65th birthday behind you, while AEP is an annual, recurring window for Medicare Advantage and Part D changes.

Bottom Line

Medicare’s enrollment structure looks complicated at first, but it comes down to two windows most people actually use: your one-time Initial Enrollment Period when you first become eligible, and the Annual Enrollment Period every fall afterward if you want to make changes.

What actually costs people money is rarely the window itself. It’s the penalty that attaches when you miss the IEP without a qualifying exception, the two-month plan deadline hiding inside an eight-month Part B deadline, and the Medigap window that quietly closes for good six months after you enroll in Part B. Those three are worth putting on a calendar. The rest you can look up when you need them.

Which window you are standing in is the part worth checking against your own record rather than a calendar. 1-800-MEDICARE can read your enrollment dates back to you, and a State Health Insurance Assistance Program counselor will work through the sequence with you for nothing. Once you know which window you are using, the Medicare Plan Finder shows what it lets you buy.

Sources

• When does Medicare coverage start? — Medicare.gov. Source for the IEP coverage start dates and for GEP coverage beginning the month after you sign up.
• Implementing Certain Provisions of the Consolidated Appropriations Act, 2021 and Other Revisions to Medicare Enrollment and Eligibility Rules — Centers for Medicare & Medicaid Services. Source for the old July 1 GEP start date and for the January 1, 2023 change that replaced it.
• Joining a plan — Medicare.gov. Source for the October 15 – December 7 AEP dates, the December 7 receipt deadline, and the January 1 – March 31 MA OEP rules.
• Understanding Medicare Advantage & Medicare Drug Plan Enrollment Periods — Medicare.gov. Source for the personal MA OEP window that runs from the first month you have both Part A and Part B through the last day of the third month.
• Special Enrollment Periods — Medicare.gov. Source for the qualifying life events, the 2-month plan enrollment windows, and the December 8 – November 30 5-star SEP.
• Working past 65 — Medicare.gov. Source for the 8-month Special Enrollment Period after employment or job-based coverage ends.
• Avoid late enrollment penalties — Medicare.gov. Source for the Part B 10% annual surcharge and the Part D 1% monthly surcharge.
• When can I buy a Medigap policy? — Medicare.gov. Source for the 6-month Medigap Open Enrollment Period starting the first day of the month you’re 65 or older and enrolled in Part B.
• Buying a Medigap policy — Medicare.gov. Source for being able to buy any Medigap policy sold in your state during that window even with health problems, and for losing that protection once it ends.

All dates, figures and rules on this page were checked against the sources above on September 15, 2026.

Disclaimer: Enrollment periods, dates, and penalty figures mentioned in this article reflect 2026 guidelines from the Centers for Medicare & Medicaid Services (CMS) and are subject to change. Always confirm current details directly with Medicare.gov, 1-800-MEDICARE, or a licensed agent before making a decision.