If you have both COBRA and Medicare, Medicare pays your medical claims first and COBRA pays second, covering what the employer plan would normally cover after Medicare’s share.1Medicare. Who Pays First That rule is simple. What trips people up is everything around it: whether you can even keep COBRA once Medicare starts, whether COBRA counts as the kind of coverage that protects you from late enrollment penalties, and what happens to your HSA, your Medigap rights, and your dependents. Getting the order wrong can cost you thousands in permanent premium surcharges or leave you holding bills neither plan fully pays.
Medicare Pays First, COBRA Pays Second
Once you’re on COBRA and entitled to Medicare, Medicare is the primary payer whether you qualified by turning 65 or through a disability. Your providers bill Medicare first, up to its coverage limits. Your COBRA plan then reviews what’s left and pays according to the employer plan’s benefits.1Medicare. Who Pays First
For services Medicare doesn’t cover at all, like most dental work or certain therapies, your COBRA plan may step in and pay as though it were primary, as long as the service falls within the employer plan’s benefits. Make sure your providers know the correct billing order. If they bill COBRA first when Medicare should go first, expect denials and delays.
This flip happens because COBRA is not active-employee coverage. While you’re still working for an employer with 20 or more employees, the group health plan pays primary and Medicare pays secondary. The moment that coverage converts to COBRA, the order reverses.2CMS. Medicare Secondary Payer
What Happens If You Skip Medicare While on COBRA
This is where the biggest bills come from. If you’re eligible for Medicare but haven’t enrolled, your COBRA plan knows it, and many COBRA plans will pay only the secondary portion of your claims. They calculate benefits as if Medicare had already paid its share, even though you never signed up.3Medicare. COBRA Coverage
Picture a $10,000 hospital stay. If Medicare were primary, it would typically cover about 80% after the deductible, and your COBRA plan as secondary would pick up most of the remaining 20%. Skip Medicare enrollment, and the COBRA plan still pays only its secondary share based on what Medicare would have paid. The primary portion lands on you.
Call your COBRA administrator and ask directly what percentage the plan pays when a member is Medicare-eligible but not enrolled. The answer almost always pushes you toward enrolling right away.
Can You Keep COBRA After Medicare Starts?
The order you enrolled in matters. If you already had Medicare (Part A, Part B, or both) when you became eligible for COBRA, you can elect COBRA and carry both for the full COBRA term. Medicare stays primary, COBRA fills gaps.4Office of the Law Revision Counsel. 26 USC 4980B – Failure to Satisfy Continuation Coverage Requirements of Group Health Plans
Go the other direction and the result changes. If you’re already on COBRA and then become entitled to Medicare, federal law allows the plan to terminate your COBRA on the date your Medicare entitlement begins.4Office of the Law Revision Counsel. 26 USC 4980B – Failure to Satisfy Continuation Coverage Requirements of Group Health Plans Some administrators act on this right immediately. Some don’t. You can’t count on keeping COBRA, so plan the transition assuming it could end the day Medicare begins. If the administrator does terminate your coverage, they must send a formal notice stating the exact end date.
COBRA Will Not Save You From Medicare Late Penalties
Part B
COBRA does not count as coverage based on current employment, and that distinction is the one that bites. Active-employee coverage gives you a Special Enrollment Period that lets you delay Part B without penalty. COBRA does not.5Social Security Administration. How to Apply for Medicare Part B During Your Special Enrollment Period
If you turn 65, leave your job, elect COBRA, and skip Part B, you’ll owe a late enrollment penalty whenever you finally sign up. It adds 10% to your standard monthly Part B premium for every full 12 months you could have had Part B and didn’t.6Medicare. Avoid Late Enrollment Penalties The standard Part B premium is $202.90 per month in 2026.7CMS. 2026 Medicare Parts A and B Premiums and Deductibles A two-year delay adds 20% to that premium for as long as you have Part B. The surcharge is permanent.
Part D
Prescription drug coverage works similarly. Go 63 or more consecutive days without creditable drug coverage after your initial enrollment window closes and you’ll owe 1% of the national base beneficiary premium ($38.99 in 2026) per uncovered month, added to your Part D premium.6Medicare. Avoid Late Enrollment Penalties Whether your COBRA drug coverage counts as creditable depends on whether it meets Medicare’s minimum standard. Your plan administrator must tell you each year.
If it is creditable, you’re protected while COBRA lasts, and you have 63 days after it ends to enroll in Part D before the penalty clock starts. If it isn’t, the penalty has been building since your initial Part D enrollment period closed. Confirm the answer now, not when you’re trying to sign up.
HSA Contributions Have to Stop
If you’ve been contributing to a Health Savings Account through a high-deductible COBRA plan, Medicare ends that. You cannot contribute to an HSA for any month you’re enrolled in any part of Medicare.8Internal Revenue Service. Individuals Who Qualify for an HSA
Retroactive enrollment makes this worse than it looks. When you apply for Part A after 65, coverage can be backdated up to six months (but never before your 65th birthday). Contributions you made during those retroactive months become excess contributions in the IRS’s eyes, and you have to withdraw them and pay any applicable taxes. The safe move is to stop HSA contributions six months before you plan to enroll in Medicare.
You can still spend existing HSA funds on qualified medical expenses, including Medicare premiums and out-of-pocket costs. The limit is only on new contributions.
Protect Your Medigap Rights Before COBRA Ends
Medigap policies normally require medical underwriting, meaning insurers can reject you or charge more based on your health. Federal law carves out guaranteed issue rights, and exhausting COBRA is one of the triggers.9CMS. Medigap Bulletin Series – Interaction Between COBRA and Medigap Guaranteed Issue Requirements
If you chose COBRA instead of buying Medigap during your initial open enrollment period, you get a second chance to buy a Medigap policy without underwriting once COBRA runs out. You generally have 63 days from the end of COBRA to apply, and some states give you longer. Insurers must sell you a policy regardless of your health and cannot charge you more than they charge healthy applicants.
Pay attention to the word “exhausts.” You must run through your full COBRA term or lose coverage because the plan terminated it. Stop paying your premiums and let COBRA lapse early, and you forfeit the guaranteed issue right.9CMS. Medigap Bulletin Series – Interaction Between COBRA and Medigap Guaranteed Issue Requirements If you’re planning to move from COBRA to Medigap, keep paying through the end.
Your six-month Medigap Open Enrollment Period is a separate thing. It starts the first day of the month you turn 65 and are enrolled in Part B, and electing COBRA during that window does not pause or restart it.10Medicare. When Can I Buy a Medigap Policy
What About Your Spouse and Dependents?
When Medicare ends your COBRA, the termination applies only to you. A spouse or dependent child on the same COBRA plan can generally continue coverage for the rest of the original COBRA period. When the qualifying event is the covered employee becoming entitled to Medicare, dependents may be eligible for up to 36 months of COBRA measured from the Medicare entitlement date.11CMS. COBRA Continuation Coverage Questions and Answers
When dependents eventually lose COBRA, losing that coverage triggers a 60-day Special Enrollment Period for a Health Insurance Marketplace plan, with coverage able to start the first day of the month after COBRA ends.12HealthCare.gov. If You Lose Job-Based Health Insurance If a dependent has employer coverage available through their own job or a new spouse’s job, a 30-day special enrollment window applies there instead.
How to Set Up the Coordination
Once both coverages are in place, make sure both sides know about each other. Pull your Medicare card, which shows your Part A and Part B effective dates, and your COBRA election notice, which carries your group plan ID.
Tell your COBRA administrator about your Medicare enrollment so claims are processed in the right order. Certified mail with return receipt gives you proof if there’s a dispute later. Many administrators also accept updates through member portals.
Report your COBRA coverage to Medicare’s Benefits Coordination & Recovery Center as well. The BCRC can be reached at 1-855-798-2627, Monday through Friday, 8 a.m. to 8 p.m. Eastern Time.13CMS. Contacts Notifying both the administrator and the BCRC heads off retroactive claim reversals, where one insurer figures out months later that it paid primary when it shouldn’t have and claws the money back.