Medicare Enrollment After COBRA Ends: Avoid Penalties

If you already had Medicare Part B before your COBRA coverage ended, you don't need to do anything differently, your Medicare stays active and COBRA simply ends. But if you delayed Part B while on COBRA, the Special Enrollment Period (SEP) tied to employer coverage almost certainly closed months before COBRA ran out, not when it did. That gap is why many people end up facing a Part B late enrollment penalty and a coverage wait they never saw coming.

COBRA, the Consolidated Omnibus Budget Reconciliation Act, lets you keep a former employer's group health plan for up to 18 to 36 months after you leave a job. The Centers for Medicare and Medicaid Services (CMS) treats that continued coverage as based on former employment, not current employment, and that single distinction decides whether you still qualify for a Medicare SEP.

Why COBRA Doesn't Reset Your Medicare Clock

Medicare's rules for delaying Part B without a penalty hinge on one phrase: coverage "based on current employment." An SEP lets you sign up for Part B any time while you, or your spouse, are actively working and covered by that employer's group health plan, plus 8 months after that coverage or the employment ends. COBRA keeps the same health plan running, but it doesn't keep you employed, so CMS doesn't count it toward the SEP.

In practice, your 8-month SEP clock starts the day your job ends, likely the same day you elected COBRA, not the day COBRA coverage runs out. If you take an 18-month COBRA plan, the SEP tied to that job loss expires 10 months before COBRA does. See how this timing plays out if you're enrolling in Medicare after losing employer coverage, or review the full list of Medicare special enrollment period qualifying events.

Two Situations, Two Different Next Steps

You're still on COBRA and haven't enrolled in Part B. Contact the Social Security Administration now. If you're within 8 months of the date your employment or employer coverage ended, you're likely still inside your SEP and can enroll in Part B without a penalty, even if COBRA continues for longer.

Your COBRA has already ended and you still don't have Part B. You'll need to wait for the General Enrollment Period, which runs January 1 through March 31 each year, with coverage starting the month after you enroll under rules CMS updated in 2023. According to Medicare.gov, the Part B late enrollment penalty adds 10% to your premium for each full 12-month period you could have had Part B but didn't, and that penalty generally lasts for as long as you have Medicare. See the Medicare general enrollment period deadlines and penalties for the exact math.

If you're approaching 65 for the first time and weighing COBRA against enrolling, read how turning 65 health coverage decisions affect this timeline, and how to delay Medicare Part B without penalty the correct way, through active employment coverage, not COBRA.

What About Part D and Medigap?

Prescription drug coverage works differently. Losing COBRA that included creditable drug coverage, meaning coverage at least as good as standard Part D, generally opens a 63-day Special Enrollment Period to join a stand-alone Part D plan or a Medicare Advantage plan with drug coverage, even if your Part B timeline follows a separate path. Keep the notice from your COBRA plan showing when drug coverage ended; you may need it as proof of creditable coverage.

Medigap, also called Medicare Supplement insurance, is a separate decision once Part B is active. Insurers in most states can use medical underwriting if you apply outside your initial 6-month Medigap window, so enrolling in Part B as soon as you're eligible protects both your timeline and your guaranteed-issue rights. Compare how Medicare Supplement premiums change by age before you decide when to apply.

Once You're Enrolled

After Part B starts, you'll choose how to structure the rest of your coverage, Original Medicare with a Medigap and Part D plan, or a Medicare Advantage plan instead. You're not locked in forever; find out when you can switch Medicare plans if your needs change later.