When you leave employer health coverage after age 65, you have an 8-month Special Enrollment Period to sign up for Medicare Part B without late penalties. Missing this window means a 10% premium increase for every 12-month period you go without Part B—a penalty that's permanent and increases your premium for the rest of your life.
The 8-Month Part B SEP Timeline
The Special Enrollment Period starts the month after either:
- You (or your spouse) stop working, OR
- The employer health coverage ends, whichever comes first
Common mistake: Many people assume the 8 months start when COBRA ends. They don't. The clock starts when active employment ends or active employer coverage ends, NOT when COBRA, retiree coverage, or severance benefits end. If you stay on COBRA for 18 months after leaving your job, your SEP will have run out.
What Coverage Triggers the SEP?
The SEP is only for coverage based on current employment—yours or your spouse's. Employer size doesn't matter for the SEP itself (it does matter for whether Medicare or the employer plan pays first).
| Coverage Type | Qualifies for SEP? |
|---|---|
| Active employer group health plan (any size) | Yes |
| Spouse's active employer group health plan | Yes |
| FEHB while you or your spouse is still a federal employee | Yes |
| FEHB as a federal retiree | No |
| COBRA continuation coverage | No |
| Retiree health coverage | No |
| ACA Marketplace or other individual coverage | No |
| Medicaid | No (but you may be dual-eligible) |
| Veterans Affairs (VA) health care | No |
| Indian Health Service (IHS) or tribal health programs | No |
Form CMS-L564: Required for SEP Enrollment
To use the Part B SEP, you need to prove you had qualifying employer coverage. Social Security requires Form CMS-L564 (Request for Employment Information), which must be completed and signed by your (or your spouse's) employer. It confirms that you had group health coverage, the dates of that coverage, and that it was based on current employment.
Steps to Complete Form CMS-L564:
- Download Form CMS-L564 from CMS.gov or get it from your local Social Security office
- Complete Section A (your personal information)
- Send the form to your former employer's HR or benefits office to complete Section B
- Submit the completed form along with Form CMS-40B (Application for Enrollment in Part B) to Social Security in person, by mail, or by fax
- Keep copies for your records
Applying Online
You can also apply for Part B during your SEP online at ssa.gov/medicare, uploading the completed Form CMS-L564 as part of the application.
When Should You Actually Enroll?
Even though you have 8 months, don't wait. The longer you delay, the longer you'll go without Part B coverage. Aim to:
- Apply 1-2 months before your employer coverage ends, so Part B starts the day after employer coverage ends
- If you sign up while you still have the employer coverage, or in the first full month after it ends, you can choose for Part B to start the first day of the month you enroll or of any of the next three months
- If you sign up later in the 8 months, Part B starts the first day of the month after you enroll
- Part B is not retroactive. Part A is: if you apply after 65, it can be backdated up to 6 months (no earlier than the month you turn 65), which matters if you contribute to an HSA
What If You Missed the SEP?
Missing the 8-month window has two consequences:
- A coverage gap: you'll have to wait for the General Enrollment Period (January 1 – March 31 each year).
- A permanent late enrollment penalty: 10% added to your Part B premium for every full 12-month period you could have had Part B but didn't, for as long as you have Part B.
Example: If you went 24 months without Part B after your SEP ended, your Part B premium would be 20% higher (2 x 10%) for life. At the 2026 standard premium of $202.90/month, that's an extra $40.58/month, or $486.96/year.
Recent change: Since 2023, Part B coverage starts the first day of the month after you sign up during the General Enrollment Period, instead of waiting until July 1. That shortens the coverage gap for late enrollees, but the penalty still applies.
Other Part B Special Enrollment Periods
Since January 2023, Medicare also offers Part B SEPs for certain exceptional situations that kept you from enrolling on time:
- Emergencies and disasters: a federal, state, or local emergency or major disaster prevented you from signing up
- Employer or health plan error: your employer or plan gave you wrong information about enrolling
- Loss of Medicaid: your Medicaid coverage ended
- Release from incarceration
- Other exceptional conditions reviewed case by case by CMS
Moving or plan changes do not open a Part B SEP; those affect Medicare Advantage and Part D enrollment instead.
Special Situations for New Mexicans
Federal Employees and Retirees with FEHB
FEHB applies to federal employees and retirees, such as those at Kirtland AFB, White Sands and DOE/NNSA. LANL and Sandia staff are contractor employees with their employer's plan, not FEHB. FEHB works like other employer coverage: the Part B SEP applies only while you (or your spouse) are still working for the federal government. After you retire, FEHB does not give you an SEP, so delaying Part B means enrolling later during the General Enrollment Period with a late penalty. For that reason, some federal retirees enroll in Part B when they retire, and some FEHB plans reduce cost-sharing when Medicare pays first. See our FEHB page.
Self-Employed New Mexicans
If you're self-employed with a Marketplace or other individual plan, that coverage is not based on current employment and does not give you a Part B SEP. Enroll in Medicare during your Initial Enrollment Period around age 65 to avoid penalties.
Native American Beneficiaries
IHS and tribal health coverage doesn't give you a Part B SEP, but enrolling in Medicare alongside IHS has real benefits: Medicare pays IHS and tribal facilities for your care, and you can also see providers outside the IHS system. See our Native American Medicare page.
Don't Miss Your 8-Month Window
The Part B SEP rules are detailed and unforgiving. A licensed insurance agent can help you coordinate your retirement date with your Part B enrollment and make sure Form CMS-L564 is filled out properly.