Who Pays First? Medicare Coordination of Benefits Explained for Dayton Retirees

A woman in Beavercreek called us last spring holding a $4,200 hospital bill she was sure was a mistake. She had Medicare. She also had coverage through her husband, who was still working at a shop in Xenia with about a dozen employees. Two cards, one bill, and nobody at the billing office could tell her why she owed anything.

It was not a mistake. It was a coordination problem — and once we sorted out which plan was supposed to pay first, most of that bill went away.

This comes up more than almost anything else we see. Here is how the order actually works.

What Coordination of Benefits Means

When you have Medicare plus one other kind of health coverage, the two plans do not split your bill down the middle. One of them is the primary payer. It pays first, up to the limits of what it covers. Whatever is left gets sent to the secondary payer. If the secondary payer does not pick up the rest, that balance is yours.

Medicare calls the rules that set this order coordination of benefits. They are federal rules. Your doctor does not get to choose, your plan does not get to choose, and you do not get to choose — the order depends on how you got your other coverage and, in some cases, on how many people your employer has on the payroll.

The single most useful thing you can do is tell every provider about every card in your wallet. When a billing office does not know a second plan exists, the claim goes to the wrong place, gets denied, and lands in your mailbox looking like a bill you owe.

Still Working: The 20-Employee Rule

This is the one that trips up the most people in the Miami Valley, and it hinges on a single number: 20.

If you are 65 or older, have Medicare, and are covered by a group health plan through your own current job or your spouse’s current job:

• Employer has 20 or more employees — the group health plan pays first, Medicare pays second.
• Employer has fewer than 20 employees — Medicare pays first, the group health plan pays second.

Both full-time and part-time employees count toward that 20. And if the employer belongs to a multi-employer plan, it counts as 20-plus as long as at least one company in that arrangement has 20 or more employees.

The practical difference is large. If you work at Wright-Patterson, GE Aviation, Premier Health, or Kettering Health, you are comfortably over 20 — your employer plan pays first, and Medicare cleans up behind it. If your spouse runs a four-person insurance office in Centerville or a small machine shop in Miamisburg, the order flips, and Medicare needs to be billed first. That was exactly the Beavercreek situation: the shop had twelve people, so Medicare should have been billed first, and it never was.

One trap worth knowing. If your employer plan is an HMO or PPO that pays first and you go outside its network, it is possible that neither the plan nor Medicare pays. Call the plan before you go out of network, not after.

Retiree Coverage and COBRA

Once the employment ends, the order reverses. If your group coverage comes from a former employer — retiree coverage, a union plan, coverage through a spouse’s old job — Medicare pays first and the retiree plan pays second.

There is a real risk buried in that sentence. Retiree plans are built assuming you enrolled in Medicare on time. If you were eligible for Medicare and did not sign up, the retiree plan may not cover the costs Medicare would have paid. You are not just missing Medicare’s share — you may be missing both. Most retiree plans require you to have both Part A and Part B to get full benefits.

COBRA works the same way. If you are 65 or older with Medicare and COBRA, Medicare pays first, and COBRA may only cover a small slice of what is left. Call your COBRA administrator and ask what percentage they actually pay. People are often startled by the answer.

TRICARE For Life

With Wright-Patterson down the road, this one matters to a lot of our neighbors.

TRICARE For Life is the expanded coverage available to Medicare-eligible uniformed services retirees 65 and older, their eligible family members and survivors, and certain former spouses. You must have both Medicare Part A and Part B to get TFL benefits. That is not optional, and it is the mistake we see most often — a retired airman assumes TRICARE alone is enough, skips Part B, and discovers the gap when a bill arrives.

If you are not on active duty, Medicare pays first for Medicare-covered services and TRICARE may pay second. If you are still on active duty, TRICARE pays first and Medicare second. And if you get care at a military hospital or clinic or any other federal provider, TRICARE pays — Medicare usually does not cover services from a federal provider.

On the drug side: most people with TRICARE who are entitled to Part A must also have Part B to keep their TRICARE drug benefits. You do not need to join a Medicare drug plan if you have TRICARE. If you do join one anyway, the Medicare drug plan pays first and TRICARE pays second. You can reach TFL directly at 1-866-773-0404.

VA Benefits Are Different

Here is the part that surprises veterans: Medicare and the VA do not coordinate at all. They generally cannot pay for the same item or service. Each time you get care, you choose which benefit you are using.

• Medicare pays for Medicare-covered items and services.
• The VA pays for VA-authorized items or services, whether at a VA facility or a non-VA one.
• If the VA authorizes services at a non-VA hospital but does not authorize everything you receive during that stay, Medicare may pay for the Medicare-covered pieces the VA did not authorize.

That last line is worth reading twice. It is why keeping Part B often makes sense for a veteran who uses the Dayton VA regularly — because care outside VA authorization is not covered by the VA, and without Part B you have nothing behind it.

On drugs, you may be able to get coverage through the VA, and you may also join a Medicare drug plan. But you cannot use both for the same drug at the same time, and joining a Medicare drug plan means you can no longer use the VA Meds by Mail program.

Workers Comp, Car Accidents, and Medicaid

Workers’ compensation pays first for anything — including drugs — related to the work injury or illness. Medicare cannot pay for items workers’ comp will pay for promptly. If the workers’ comp carrier denies the bill while reviewing the claim, Medicare may make what it calls a conditional payment, and expects to be paid back later.

Car accidents. If no-fault or liability insurance is involved, that insurance pays first and Medicare pays second for anything related to the accident. Your provider is supposed to bill the auto carrier before Medicare. Because these cases can drag, Medicare may make a conditional payment in the meantime and recover it once the case settles.

Medicaid always pays last. For services Medicare covers, Medicaid never pays first. If you have Ohio Medicaid alongside Medicare, Medicare goes first, and in the rare case where there is a third source of coverage, Medicaid pays after that one too.

Under 65 on Medicare

If you have Medicare because of a disability rather than age, the employer threshold changes from 20 to 100. With current employment-based coverage through an employer with 100 or more employees — what Medicare calls a large group health plan — the plan pays first and Medicare pays second. Under 100, Medicare pays first.

End-Stage Renal Disease follows its own clock. If you qualify for Medicare because of ESRD and you have group health coverage based on current or former employment, the group plan pays first for a 30-month coordination period — regardless of how many employees the company has, and regardless of whether the coverage is tied to a current job. After those 30 months, Medicare pays first for all Medicare-covered services. This holds even if the employer plan document claims its benefits are secondary to Medicare.

What to Do This Month

Three things, and none of them take long.

Count the employees. If you or your spouse are still working, find out how many people are on that payroll. Twenty is the line at 65 and over; one hundred if Medicare came through disability. Your benefits administrator can answer this in one phone call.

Hand over every card. At every appointment. Most coordination problems are not disputes — they are billing offices working with incomplete information.

Call the Benefits Coordination and Recovery Center if your coverage changes. New job, retirement, a spouse retiring, a new plan — Medicare needs to know so its records show the right primary payer. The number is 1-855-798-2627, or 1-855-797-2627 for TTY users.

One more note for anyone weighing whether to keep Part B while other coverage is in the picture: the 2026 Part B standard premium is $202.90 a month, with a 2026 annual deductible of $283. That is a real cost, and for some people with small-employer coverage or TRICARE, it is also the thing standing between them and a bill nobody will pay.

If you are holding a statement you do not understand, or you are about to retire and are not sure which plan becomes primary, we are happy to look at it with you. Medicare and Retirement Solutions Group is right here in Beavercreek, the consultation is free, and there is no obligation. Give us a call or reach out through medretiregroup.com. Bring the bill.

This article is general educational information, not individualized tax, insurance, or investment advice. Rules and figures change and individual circumstances vary — please confirm details with your plan, or speak with a qualified professional, before acting.