Medicare Special Enrollment Periods: Which One Is Yours (2026)

A Medicare Special Enrollment Period reopens your enrollment window after a qualifying life event, and knowing which one is yours, before it closes, can save you a lifetime penalty. The costliest mistake here is quiet: someone retires past 65, takes COBRA, and assumes it holds their Medicare window open. It does not. This guide maps each life event to its window.

In This Guide

• Key Takeaways
• Which Medicare Special Enrollment Period Is Mine?
• Working Past 65: The 8-Month Window and the COBRA Trap
• Losing Medicaid or Extra Help
• The Five Exceptional-Conditions SEPs
• Changing Your Plan: Move, 5-Star, Plan Exit, Disaster
• What If You Miss Your Medicare Special Enrollment Period?
• Frequently Asked Questions
• Learn More

Which Medicare Special Enrollment Period Is Mine?

Medicare runs on a set calendar of enrollment windows, and Special Enrollment Periods are the exceptions certain life events unlock.4 Find your situation below, then read the section that matches it.

Working Past 65: The 8-Month Window and the COBRA Trap

This is the SEP that costs families the most, because the trap is invisible until the bill arrives.

If you or your spouse are still working and you have group health coverage based on that current employment, you can delay Part B without penalty and enroll later. CMS calls this the Special Enrollment Period for the Working Aged and Working Disabled, and it is not limited to you or a spouse: if you are under 65 and disabled, coverage based on a non-spouse family member's current employment also qualifies, provided that plan is a large group health plan, which Medicare defines as covering an employer or employee organization with at least 100 employees. Not every job-based plan counts, either. Medicare gives this guidance for group health insurance available to everyone at the company, and tells people who are self-employed, or whose plan is not, to ask their insurer whether it is employer group health plan coverage as the IRS defines it, and to sign up at 65 if it is not. Three situations disqualify you outright: being eligible for Medicare based on End-Stage Renal Disease (ESRD), having the group coverage or the job it is based on end during your Initial Enrollment Period, and relying on Marketplace coverage, which Medicare lists among the situations that do not qualify. Part D runs on a separate clock too: this Special Enrollment Period does not extend Part D deadlines, and the Part D penalty is triggered by going 63 days or more without creditable drug coverage, so check whether your employer drug coverage is creditable rather than assuming the Part B window covers it.1

When that employment ends, you get an 8-month Special Enrollment Period to sign up for Part B, and its start is the one point on which Medicare's own agencies differ: CMS counts the eight months from the month your employment ends or the employer coverage ends, whichever comes first, while Social Security counts from the month after that. Count from the earlier one, so your window closes eight months after the job or the coverage ends.1 That timing decides everything, because COBRA and retiree coverage do not count as current-employer coverage. If you retire, take COBRA for a few months, and wait for COBRA to end before signing up for Part B, your 8-month clock has been running the entire time, and it may have already expired.

That does not close the door on every post-employment plan, though. Social Security lists group health plan coverage based on severance or retirement pay as a qualifying situation in its own right, bounded by its own condition: the job that coverage is based on must have ended in the last eight months. Social Security frames these as situations where you may qualify, not as guarantees, so confirm your own case with them.1 Separately, under Medicare's payer rules a reemployed retiree or annuitant who performs enough services to qualify for the group plan on that basis counts as covered by reason of current employment status, even if the employer gives retirees that same plan or the premiums come from a pension fund.5

When you do sign up, coverage under this Special Enrollment Period generally starts the first month after you sign up. If you sign up for Part B while you're still working, or within the first full month after the employer coverage ends, you can ask to delay your Part B start date up to 3 months.1

Employer size does not decide whether this SEP exists, but it decides who pays your bills while you delay. Under Medicare's Secondary Payer rules, if the employer has at least 20 employees, the group health plan pays first and Medicare pays second, which is what makes delaying Part B safe. If the employer has fewer than 20 employees, Medicare generally pays first, so enrolling during your Initial Enrollment Period is usually safer. A multi-employer plan in which at least one participating employer has 20 or more employees also puts the plan first, but that carries an exception you have to ask about: the plan may request an exception for someone covered through an employer with fewer than 20 employees, and Medicare's own guidance is to check with your plan and ask whether it will pay first or second for your claims. And if you refuse the plan your employer offers, Medicare becomes your primary payer and the plan may not offer you coverage complementary to Medicare.5

Missing your Part B window triggers a lifetime penalty. The Part B late-enrollment penalty adds 10% to your monthly premium for each full 12-month period you could have had Part B but did not, and it lasts for as long as you have Part B, unless you qualify for a Special Enrollment Period or for a Medicare Savings Program.6 Since the 2026 standard Part B premium is $202.90 a month, a two-year gap means paying roughly 20% more, every month, for life.6 Our guide to the late-enrollment penalties walks through each part's penalty and the exception attached to it.

Losing Medicaid or Extra Help

If you had Medicaid or Extra Help with drug costs and then lost it, two separate things happen, and it helps to keep them apart. First, losing Medicaid opens an exceptional-conditions SEP, and its start is the part people get wrong. It does not begin when your coverage ends: it begins when you are notified that your Medicaid is being terminated, and it runs through 6 months after the termination, so the window is usually longer than six months end to end. You have to be able to show that your Medicaid eligibility is being terminated on or after January 1, 2023, and CMS states you are not eligible for this SEP if you are still eligible for Medicaid, including through a Medicare Savings Program, and have not received notice of an upcoming termination. You can also ask that your Part B entitlement be backdated to the date your Medicaid ended, if you pay the premiums for those months.2 Your state's State Health Insurance Assistance Program (SHIP) can help you document the loss and act inside the window, which matters most for people who lost coverage at a Medicaid eligibility renewal.

Second, if you still have Medicaid or Extra Help, you can change your drug coverage far more often than most people can. A 2025 Medicare rule replaced the old once-per-quarter window with a once-per-month one, so people with Medicaid or a low-income subsidy can elect a standalone Part D drug plan in any month of the year. One exclusion sits on the face of that rule: if you have been notified that you have been identified as a potential at-risk or at-risk beneficiary under Part D's drug management program, you cannot use it until that identification is terminated.3 If you have full Medicaid, a separate monthly window also lets you move into an integrated plan built for people who have both Medicare and Medicaid. For the help itself, see Medicare Savings Programs and our guide to Extra Help.

The Five Exceptional-Conditions SEPs

Effective January 1, 2023, Medicare added a set of Special Enrollment Periods for people who missed their enrollment because of something outside their control. Coverage generally begins the first day of the month after you enroll, with two backdating exceptions noted below. Two conditions travel with all five. None of them is automatic: you have to demonstrate that you meet that SEP's conditions. And the late-enrollment penalty relief is not blanket, it is tied to acting in time. The months you went without coverage are excluded from the penalty calculation only if you enroll within the SEP's window, so letting the window lapse means those months, including the months of the SEP itself, count against you.2 There are five, and each has its own window:

• Your Medicaid is being terminated. As above: it begins at your termination notice, ends 6 months after the termination, and allows backdating to the date Medicaid ended if you pay those premiums.
• An employer, health plan, or one of their agents or brokers gave you wrong information. A 6-month SEP starting the day you notify Social Security. You have to show, by documentation or written attestation, both that you did not enroll based on that information and that the employer, plan, or agent materially misrepresented or gave you incorrect information.
• You were released from incarceration. An SEP that runs through the last day of the 12th month after the month you were released. You can instead choose an effective date backdated up to 6 months, never earlier than the month of release, and you owe the premiums back to that date. People released to and living in halfway houses are not treated as incarcerated for this SEP.
• A declared emergency or disaster affected you. It begins on the earlier of the declaration date or the start date named in the declaration, and ends 6 months after the declaration ends. You have to show you lived in the declared area during the period it covered, and that the disaster prevented you from filing a timely enrollment request.
• Another exceptional condition. A catch-all Medicare decides case by case, lasting no less than 6 months, for an event outside your control that made you miss an enrollment period. CMS states it is granted only where the conditions are truly exceptional and will not be used for forgetfulness, lack of knowledge, or failure to make premium payments.2

Two more Part A and Part B Special Enrollment Periods sit alongside these five on Medicare's own list. One is for international volunteers: if you did not enroll while serving outside the United States for at least 12 months for a tax-exempt organization, and had health insurance for the duration, you get a 6-month window beginning at the earliest of your service ending, the organization losing tax-exempt status, or that insurance ending. The other is for people who enrolled in Part A because of disability or ESRD but skipped Part B because they were eligible for TRICARE Standard or TRICARE Prime; Medicare's consumer page and CMS describe its timing differently, so ask Social Security for your own dates.1

These SEPs came from the Consolidated Appropriations Act, 2021 and sit in two parallel sections of the rules: 42 CFR 407.23 for Part B, and 42 CFR 406.27 for premium Part A.2 To use one, you apply through the Social Security Administration on Form CMS-10797, which is the application for the exceptional-conditions SEPs only; the working-aged and working-disabled SEP uses different forms, CMS-18-F-5 or CMS-40B, plus the employer verification form CMS-L564.1 If your situation is not one of the named categories, be ready to explain why it was genuinely exceptional.

Changing Your Plan: Move, 5-Star, Plan Exit, Disaster

The SEPs above are mostly about getting into Medicare on time. A second group is for people already in Medicare who need to change a Medicare Advantage or Part D plan off-calendar.7

• You moved out of your plan's service area. If you tell your plan before you move, your window to switch begins the month before the move and runs 2 full months after; if you tell them after, it begins the month you move and runs 2 full months after.
• A 5-star plan is available near you. You can switch into a 5-star-rated Medicare Advantage, Part D, or Cost plan once, any time from December 8 of the year before the plan year through November 30 of the plan year, and only if a 5-star plan is actually available in your area. Medicare attaches two warnings to it. If you move from a Medicare Advantage plan that includes drug coverage into a stand-alone Medicare drug plan, you will be disenrolled from the Medicare Advantage plan, including the health benefit, and returned to Original Medicare for your health services. If you move from a Medicare Advantage plan that has drug coverage into a 5-star Medicare Advantage plan that does not, you may lose your prescription drug coverage, have to wait until your next enrollment opportunity to get it back, and have to pay a Part D late enrollment penalty. Our guides to the 5-star Special Enrollment Period and Medicare star ratings go further.
• Your plan's contract with Medicare is ending. The window depends on who ended it. Medicare terminates the contract: 1 month before it ends through 2 full months after. Your plan ends it, or your plan and Medicare agree to: 2 months before through 1 full month after. The contract simply is not renewed: December 8 through the last day of February the following year.
• A disaster or emergency got in your way. If a federal, state, or local government declares an emergency or disaster that kept you from acting during another enrollment period, you may get an SEP to join, switch, or drop a plan. It starts at the earliest of the declaration date, the incident start date, or a start date named in the declaration, and ends 2 full calendar months after the declaration's end date. That is shorter than the 6-month disaster SEP for Part B enrollment above, so do not use one window's deadline for the other.7

What If You Miss Your Medicare Special Enrollment Period?

Before you accept that the door is closed, check the misrepresentation SEP above. An employer or health plan telling someone they did not need Part B is the commonest way a person misses this deadline, and that SEP gives you six months from the day you notify Social Security with no late-enrollment penalty at all.2 There is also a narrow regulatory exit: failing to enroll during an available SEP generally means you get no additional ones, but a failure caused by your group health plan coverage being restored before that SEP ended does not preclude additional SEPs.1

If none of those fits, your fallback is the General Enrollment Period, which runs January 1 through March 31 each year.1 For sign-ups dated January 1, 2023 or later, coverage from a General Enrollment Period sign-up begins the first day of the month after you enroll, replacing the old rule that left coverage effective the following July 1, and a late-enrollment penalty may apply.1 For prescription drugs, going without creditable coverage adds 1% of the national base beneficiary premium ($38.99 in 2026) for each month you went without, for as long as you have Part D; there is generally no Part D penalty if you have creditable drug coverage or qualify for Extra Help.6 For the regular calendar rather than a life-event window, our overview of Medicare enrollment periods walks through all of them.

Learn More

Find personalized help figuring out which Medicare Special Enrollment Period applies to you at brevy.com.

The information on Brevy.com is for educational purposes only and is not a substitute for professional legal, financial, or medical advice. Rules vary by state and program and change frequently. Always verify with the relevant agency or a qualified professional. Brevy is not a law firm, financial advisor, or healthcare provider.