You have Medicare and health insurance through your spouse’s job, or maybe through a family member’s plan. You show both cards at your doctor’s office when you go in for health care. A few weeks later, you get a bill, or a notice that a claim wasn’t paid the way you expected.
The problem may not be your coverage. Insurance companies follow formal Coordination of Benefits (COB) rules to decide which plan pays first, and the claim may simply have gone to the wrong one. These COB rules exist mainly to prevent duplicate payments for the same service, not to reduce your coverage.
When you have Medicare and another health plan, Coordination of Benefits rules decide which plan pays first. Getting this order right can prevent delays, denied claims, and confusing bills. Here’s how the rules work, and what to check before your next appointment.
A primary payer is the insurance that receives and processes your claim first. According to Medicare.gov, the primary payer “pays up to the limits of its coverage.”
A secondary payer steps in after that. It may pay some or all of what’s left, but only for covered services under its own plan. A secondary plan does not automatically pay every remaining dollar.
Here’s a simple example. Say your primary plan covers 80% of a $200 office visit and pays $160. Your secondary plan may then cover part or all of the remaining $40, depending on its own coverage rules for covered services.
If a claim goes to the wrong plan first, or your provider has outdated insurance information, a few things can happen. A claim can be delayed. A claim can be denied or rejected. Your provider’s office may ask you for updated information. A bill can arrive before the mix-up gets fixed.
This doesn’t mean every unexpected bill points to a coordination problem. But a wrong billing order is one of the more common reasons a claim gets stuck between two insurance companies.
No single rule covers everyone. The order depends on your age, why you’re eligible for Medicare, whose job the coverage comes from, and how many people that employer has. If you’re a federal employee or retiree with coverage through the Federal Employees Health Benefits (FEHB) program, the same current-employer and retiree rules below generally apply to you too.
These are general patterns, not guarantees, according to the Centers for Medicare & Medicaid Services (CMS). A few exceptions can change the order.
Some employers join multi-employer plans. If even one participating employer meets the size threshold, CMS generally treats the whole plan as if it does too, unless the group has an approved small employer exception. That exception never applies to End-Stage Renal Disease (ESRD). During the first 30-month ESRD coordination period, the group health plan pays first no matter your age or employer size. After 30 months, Medicare becomes primary.
No-cost, unbiased service
Compare all major plans and carriers
Local, licensed insurance agents with 25+ years of combined experienceThe same age, employment, and ESRD rules decide payment order whether you have Original Medicare or a Medicare Advantage plan. What changes is who processes the claim.
When Medicare is primary, your Medicare Advantage plan pays claims in Medicare’s place, covering the same covered services and health benefits your plan promises. When Medicare is secondary, your Medicare Advantage plan is secondary too. One nuance is worth knowing. Some employers and unions provide retiree coverage through a Medicare Advantage plan itself, called an Employer Group Waiver Plan. If that’s your situation, your retiree benefit and your Medicare coverage are one combined plan, not two separate health insurance plans to coordinate.
Agent tip:
“If your retiree benefits come through an Employer Group Waiver Plan (EGWP), you don’t have two separate insurance plans to coordinate — Medicare and your retiree coverage are combined into one plan. A licensed insurance agent can help you confirm which situation applies to you.”
If you’re dual eligible — enrolled in both Medicare and Medicaid — the who-pays-first question has a simpler answer than the employer scenarios above. According to Medicare.gov, Medicaid is always the payer of last resort. That means Medicare pays first for any service both programs cover, and Medicaid only steps in afterward to help with what Medicare doesn’t pay, such as remaining deductibles, coinsurance, or copays.
So if you’ve been searching for who pays first, Medicaid or Medicare, the short version is: Medicare goes first, every time, for services it covers. This holds true whether you have Original Medicare or a Medicare Advantage plan, and it doesn’t change based on your employer or your spouse’s employer the way the rules above do.
In practice, most providers use an automated “crossover” process: they bill Medicare first, and Medicare electronically forwards the claim details to Medicaid for any remaining balance. You generally don’t need to submit anything yourself, but it’s still worth confirming with your provider’s billing office that both your Medicare and Medicaid information are on file and current, especially after a move or a change in your Medicaid case number.
Use this checklist before your visit:
At check-in, you can ask: “I have Medicare and another health plan. Can you confirm which insurance you have listed as primary?”
If your records look wrong, contact Medicare’s Benefits Coordination & Recovery Center at 1-855-798-2627 (TTY: 1-855-797-2627). This office tracks your Coordination of Benefits (COB) and can correct outdated information. A licensed insurance agent cannot change these official records, but can help you understand your options across your health insurance plans. Not sure how Medicare works with your other coverage? Call (623) 223-8884 to speak with a licensed insurance agent.
If you’re still working past 65 and weighing your enrollment timing, see What is the Medicare Initial Enrollment Period?
Before your next appointment, confirm which plan pays first and make sure your provider has current information for both. That one step can prevent most billing problems tied to coordination of benefits.
No single rule determines who pays first; it depends on your age, why you have Medicare, and your employer’s size. The good news: once you know your situation, checking it is simple. Confirm your employer’s size, make sure Medicare’s records are current, and bring both cards to check-in. That one habit prevents most billing surprises tied to coordination of benefits and keeps your covered services and health benefits flowing without a hitch.
No-cost, unbiased serviceCompare all major plans and carriers Local, licensed insurance agents with 25+ years of combined experience
No. Medicare pays first for most retirees. But current employer coverage can pay first instead, depending on employer size and why you qualify for Medicare.
It depends on your employer’s size. Employers with 20 or more employees usually pay first for age-based Medicare. Smaller employers usually mean Medicare pays first.
The 20-employee rule applies, based on that family member’s employer size. A larger employer plan usually pays first; a smaller one usually means Medicare pays first.
Yes. According to Medicare.gov, Medicare pays first and retiree group health coverage pays second, whether the retiree coverage is yours or a family member’s.
Medicare pays first. According to Medicaid.gov, Medicaid is always the payer of last resort, so it only pays after Medicare and any other coverage have paid their share.
Contact Medicare’s Benefits Coordination & Recovery Center at 1-855-798-2627 to confirm your current records, or ask your provider’s billing office which plan they list as primary.
Read more by Renee van Staveren
Since 2009, I've been writing about complicated, technical issues, with the goal of making topics like Medicare and healthcare easier to understand. I've been writing about Medicare since 2021 and healthcare since 2019. I am an AmeriCorps alumni. I enjoy gardening, reading, and DIYing.
Call Now
