Medicare Coordination of Benefits: Who Pays First

When you have Medicare and other insurance, coordination of benefits (COB) decides which plan pays first. That plan is the primary payer. The other is the secondary payer, and it pays only for costs the primary payer didn't cover. Which one is primary depends on your age, your job, the size of your employer, the reason you qualify for Medicare and whether an accident or work injury is involved.

The short version is below. The details, with examples, follow.

TL;DR

• The primary payer pays up to its limits. The secondary payer pays only what it covers of the remainder, and you may still owe costs neither plan covers (Medicare.gov).
• At 65 or older with employer coverage from current work, the employer plan pays first if the employer has 20 or more employees. Medicare pays first if it has fewer than 20 (CMS).
• COBRA and retiree coverage generally pay second to Medicare, except during the first 30 months of end-stage renal disease (ESRD) entitlement.
• Workers' compensation, no-fault and liability insurance pay first for related injury care.
• Tell Medicare and your providers whenever your coverage or job changes, so claims are paid in the right order.

Table of Contents

• How coordination of benefits works
• Who pays first: the quick reference
• Employer coverage when you're 65 or older
• Disability and Medicare
• COBRA and retiree coverage
• End-stage renal disease (ESRD)
• Workers' compensation, no-fault and liability insurance
• Medicaid, supplements and other coverage
• What to do when claims are paid in the wrong order
• Keeping your coordination information current
• Perspective
• Get help sorting out who pays first
• FAQ
• Sources

How coordination of benefits works

Coordination of benefits is the set of rules that sets the payment order when Medicare and other coverage exist together. CMS describes the federal Medicare Secondary Payer (MSP) program as applying when Medicare isn't primarily responsible because another entity must pay first, and it expects entities billing Medicare to determine whether Medicare is primary (CMS).

The process works like this:

1. Your provider bills the primary payer first.
2. The primary payer pays up to its coverage limits and passes the remainder along.
3. The secondary payer pays only if it covers the remaining costs.
4. You owe whatever neither plan covers.

CMS's COB process also shares Medicare eligibility data with other payers. It can send Medicare-paid claims to supplemental insurers when a crossover agreement exists. It is designed so that combined payments never exceed 100% of the claim (CMS).

The order isn't a matter of preference. It depends on the type of coverage, your age, whether you're retired, whether you have a disability and whether you have ESRD (Medicare.gov publication).

Who pays first: the quick reference

These rules come from CMS's Medicare Secondary Payer page. Your own plan documents and the Benefits Coordination & Recovery Center (BCRC) can confirm how they apply to you.

Employer coverage when you're 65 or older

This is the most common case for people turning 65 who are still working, or whose spouse is.

• Employer has 20 or more employees: the employer plan pays first and Medicare pays second.
• Employer has fewer than 20 employees: Medicare pays first.

The rule applies to coverage based on current employment. Coverage you or a spouse gets through active work counts. Retiree coverage generally doesn't, and in that case Medicare is usually primary.

Example: Dana is 66 and works for a 150-person company with a group health plan. Her employer plan is primary and Medicare is secondary. Her husband, Tom, is 67 and works for a 12-person company. For him, Medicare is primary.

This is why the timing of Part B matters. If you're working past 65 at a large employer, you may be able to delay Part B without a penalty. If you're at a small employer, delaying can leave you with claims that the employer plan expects Medicare to pay. Check with your benefits administrator before deciding. We can help you sort it out (see our Medicare page).

Disability and Medicare

If you're under 65 and entitled to Medicare because of a disability, the group plan pays first when it comes from current employment (yours or a family member's) and the employer has 100 or more employees (CMS). Below that size, Medicare is generally primary.

A change in the reason for entitlement matters too. If you first became entitled because of age or a non-ESRD disability and later qualify based on ESRD, the coverage that paid first when Medicare began continues to pay first (Medicare.gov publication).

COBRA and retiree coverage

COBRA continuation coverage is often misunderstood. If you have Medicare because of your age or a disability and you also have COBRA, Medicare generally pays first and COBRA pays second (CMS).

That has a practical consequence. Someone who leaves a job, keeps COBRA and skips Part B can face claims that go largely unpaid, because COBRA expects Medicare to be primary. If you're leaving work near 65, read your options before the coverage ends. Our guide to health insurance before Medicare covers the bridge years, and Medicare's Special Enrollment Period rules may apply when employer coverage ends (our SEP articles).

End-stage renal disease (ESRD)

ESRD flips the usual order. For people entitled to Medicare based on ESRD, Medicare is secondary to a group health plan for 30 months, whatever the employer's size and whether or not the coverage is from current employment. That includes COBRA and retirement-plan coverage, even when the plan says it is secondary to Medicare (CMS).

After the 30 months, Medicare becomes primary. Plan for that change so there's no gap. Our article on the Medicare ESRD 30-month rule walks through it.

Workers' compensation, no-fault and liability insurance

For care related to a job injury or illness, workers' compensation pays first. For care related to an accident, no-fault or liability insurance pays first. CMS lists liability coverage as including self-insurance, automobile, homeowners', product, malpractice, uninsured-motorist and underinsured-motorist policies (CMS coordination workbook).

Conditional payments

If the insurer doesn't pay promptly, usually within 120 days, your provider may bill Medicare (Medicare.gov). Medicare may make a conditional payment so you aren't left without care. Once a settlement, judgment or award is paid, Medicare must be repaid (CMS).

If workers' compensation denies a claim because the service isn't something it covers, Medicare may consider a Medicare-covered claim. The reason for the denial matters.

If you're in an accident or file a workers' compensation claim, notify the BCRC, and tell your attorney about Medicare's recovery right.

Medicaid, supplements and other coverage

Medicare's recovery rights take priority over any other party, including Medicaid (CMS MLN). If you have both programs, see when Medicaid and Medicare both pay.

People paying for long-term care also run into payer-order questions, since Medicare covers little of it. This overview of Medicaid and long-term care insurance explains how those pieces fit together.

Medicare Supplement (Medigap) plans work differently. They follow Medicare's payment through the crossover process and fill in cost-sharing. Medicare Advantage replaces Original Medicare, so your plan's own rules apply. If you have Advantage and other coverage, ask both insurers how they coordinate.

Coverage questions for specific treatments follow the same logic. Whether a therapy is covered by Medicare or private insurance depends on the treatment and the plan, as in this look at PRP therapy coverage.

What to do when claims are paid in the wrong order

Wrong order, denials and delays happen most often after a coverage change. Work through this list:

1. Check who should be primary. Use the table above and your plan documents.
2. Bill in order. When Medicare is secondary, the claim goes to the primary insurer first. If it doesn't pay in full, submit it to Medicare for secondary consideration with the primary insurer's explanation of benefits (Novitas Solutions).
3. Call the BCRC. Call 1-855-798-2627 (TTY 1-855-797-2627) for questions about who pays first or coverage changes (Medicare.gov).
4. Appeal a denial if needed. For Original Medicare Part A or B, the steps are redetermination, reconsideration by a Qualified Independent Contractor, an administrative-law-judge hearing, Appeals Council review and possible federal-court review (42 C.F.R. §405.904).

Know that recovery can run both ways. CMS may recover incorrect payments from a primary payer, another entity or a third payer. A primary payer generally has 60 days to reimburse Medicare after CMS receives information that it has paid or could pay. Interest may apply afterward (CMS MLN).

Keeping your coordination information current

Medicare relies on what it has on file. CMS asks you to answer Medicare Secondary Claim Development Questionnaires promptly, tell the BCRC about changes in coverage tied to current employment, and tell providers about other coverage (CMS). Retirement and a change of insurance company can both affect how claims are paid.

Report these events:

• You or your spouse retire or change jobs.
• Employer coverage ends or changes.
• You start or stop COBRA.
• You're in an accident or file a workers' compensation claim.
• A lawsuit involving a medical claim begins.

Perspective

Most coordination problems we see aren't caused by the rules. They're caused by timing. Someone retires, keeps a plan they assumed was primary, and then finds out months later that claims are stuck.

Our advisors are licensed with multiple carriers, so we can compare your options without steering you toward one company. Before you drop employer coverage, delay Part B or enroll in a Medicare Advantage or Supplement plan, we look at which plan will actually pay first in your situation.

We also stay with you after enrollment. When your job, health or household changes, we help you update your coverage so it keeps matching your needs. Our guidance is at no cost to you.

Brian

Get help sorting out who pays first

If you're turning 65, retiring or changing jobs in Michigan, we can walk through your coverage and help you choose Medicare Advantage, Medicare Supplement or Part D plans that fit alongside what you already have. Start with our Medicare services. If you want to plan ahead for next year, our Michigan Medicare plan checklist is a good place to begin.

Have questions? We have answers! Contact us to schedule a no-obligation meeting.

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FAQ

Is Medicare always primary?

No. Medicare is primary in many cases, such as retiree coverage, COBRA after age or disability entitlement, and employer plans at small employers. It is secondary when a large employer's plan from current work covers you, or in ESRD, workers' compensation, no-fault and liability situations.

Who pays first if I'm still working at 65?

If your employer has 20 or more employees, the employer plan pays first and Medicare pays second. If it has fewer than 20, Medicare pays first. Confirm your employer's size and plan rules with your benefits office.

What happens if Medicare and my other insurer both deny a claim?

Look at the denial reason, since Medicare may consider a covered claim when the primary payer denies responsibility. You can call the BCRC at 1-855-798-2627 and appeal through the Medicare process if Medicare denies it.

Who do I call to update my other insurance information?

Call the Benefits Coordination & Recovery Center at 1-855-798-2627 (TTY 1-855-797-2627). Also tell your doctors and pharmacy about any other coverage you have.

Sources

• How Medicare works with other insurance, Medicare.gov
• Medicare Secondary Payer, CMS
• Coordination of Benefits, CMS
• How Medicare Works with Other Insurance, Medicare.gov publication
• End-Stage Renal Disease, CMS
• Coordination of Benefits workbook, CMS
• Reporting Other Health Insurance, CMS
• MLN006903 Medicare Secondary Payer, CMS
• Medicare secondary payer billing, Novitas Solutions
• 42 C.F.R. §405.904, eCFR

Recommended

• Medicaid vs. Medicare: When Both Pay and How to Apply in the U.S.
• Medicare Home Health Coverage: What's Covered and Who Qualifies
• Avoid Gaps: Medicare ESRD Coverage and the 30-Month Rule
• Medicare at 65: Avoid Part D Penalties and Check 2026 Costs