Part B Special Enrollment Period

After losing qualifying employer coverage, you have an 8-month Special Enrollment Period to enroll in Medicare Part B without the late enrollment penalty. The clock starts when employer coverage ends, NOT when COBRA ends. Form CMS-L564 must be completed by your former employer to prove qualifying coverage.

The 8-Month Special Enrollment Period

If you delayed Medicare Part B enrollment because you had qualifying employer coverage, you get a Special Enrollment Period (SEP) to enroll in Part B when that coverage ends - without paying the 10% per year late enrollment penalty.

The 8-month SEP starts:

• The month after your employment ends, OR
• The month after your group health coverage ends
• Whichever happens FIRST

Form CMS-L564: Proof of Coverage

To enroll in Part B during the SEP, you need to submit Form CMS-L564 to Social Security. This form must be completed by your former employer's HR department and verifies that:

• You (or your spouse) had qualifying employer group health coverage
• The dates of that coverage
• Whether it was based on current employment

Steps to enroll using the SEP:

1. Get Form CMS-L564 from CMS.gov or your local Social Security office
2. Have your former employer complete it (HR or benefits administrator)
3. Complete Form CMS-40B (the Part B enrollment application)
4. Submit both forms to Social Security in person, by mail, or by fax
5. Part B coverage starts the month after you enroll (or up to 3 months later if you choose)

Online Enrollment

Since 2022, you can also enroll in Part B online during your SEP at ssa.gov/medicare. You'll need to upload Form CMS-L564 as part of the online application.

What Happens If You Miss the 8-Month SEP?

Two bad things:

1. Permanent Part B late enrollment penalty: 10% added to your Part B premium for every full 12 months you could have had Part B but didn't enroll. This is permanent for the rest of your life.
2. Coverage delay: You can only enroll during the General Enrollment Period (January 1 - March 31 each year), with coverage starting July 1 of the same year.

Example penalty calculation: If you delayed Part B for 24 months after your SEP ended, your Part B premium would be 20% higher (2 x 10%) - permanently. At the 2026 standard premium of $202.90/month, that's an extra $40.58/month, or $486.96/year for life.

SEPs You Might Not Know About

Beyond the standard 8-month SEP after losing employer coverage, you may qualify for other SEPs:

• Reduction in hours: If your hours are reduced and you lose employer coverage
• Becoming Medicare-eligible due to disability after 65: Separate SEP rules apply
• Moving: Permanently moving outside your plan's service area
• Loss of coverage due to plan termination: If your employer drops coverage entirely
• Dual-eligible status changes: Gaining or losing Medicaid eligibility
• Natural disasters or emergencies: CMS may grant SEPs during declared emergencies

Special Situations for New Mexicans

Federal Retirees from LANL, Sandia, Kirtland

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 (January 1 to March 31) with a late penalty. Many federal retirees enroll in Part B when they retire for that reason, and because it reduces FEHB cost-sharing significantly. See our FEHB page.

Self-Employed New Mexicans

If you're self-employed with a marketplace plan, your coverage is NOT creditable for Part B purposes. You must enroll in Medicare during your Initial Enrollment Period at 65 to avoid penalties.

Native American Beneficiaries

IHS coverage doesn't count as creditable for Part B, but enrolling in Medicare alongside IHS provides significant benefits (Medicare reimburses IHS facilities, expands your provider access, etc.). See our Native American Medicare page.