Medicare Secondary Payer Rules: When Medicare Pays Second

Medicare Secondary Payer (MSP) is a set of federal laws that govern which payer is responsible for paying first when a Medicare beneficiary has more than one source of health coverage. The term "primary payer" refers to the insurer that pays first. The "secondary payer" pays after the primary payer has processed the claim, covering some or all of the remaining balance.

Congress enacted the MSP statute in 1980 to reduce federal spending by ensuring that Medicare does not pay for services that another insurer is legally required to cover. Since then, the rules have expanded significantly and now cover a wide range of situations including employer group health plans, COBRA, workers compensation, no-fault auto insurance, liability insurance, and the Veterans Administration.

For Medicare beneficiaries, understanding MSP rules is essential for three reasons:

The Centers for Medicare and Medicaid Services (CMS) maintains a Medicare Secondary Payer overview with official guidance for providers, insurers, and beneficiaries.

The most common MSP situation involves people who are 65 or older and still working, covered by an employer group health plan (GHP) through their own job or their spouse's job.

The employer size rule:

If your employer has 20 or more employees, the employer plan is the primary payer and Medicare is secondary. This means you can safely delay enrolling in Medicare Part B without penalty, as long as you remain covered by the employer plan. When that employer coverage ends (because you retire, lose your job, or the employer drops coverage), you have a Special Enrollment Period of up to eight months to enroll in Part B without a late enrollment penalty.

If your employer has fewer than 20 employees, Medicare is the primary payer. In this case, you should enroll in Medicare Part B at 65 even if you have employer coverage. The employer plan may refuse to pay for services that Medicare should have covered, leaving you with the full bill.

Important nuances:

COBRA allows you to continue employer group health plan coverage for up to 18 months after leaving a job (or up to 36 months in some circumstances). The MSP rules for COBRA are straightforward but frequently misunderstood.

Medicare is always primary over COBRA. If you have both Medicare and COBRA, Medicare pays first and COBRA pays second, regardless of which one you enrolled in first.

This creates an important practical issue: if you are enrolled in COBRA and then become eligible for Medicare (for example, you turn 65 while on COBRA), you should enroll in Medicare Part B. If you do not enroll in Medicare and continue relying on COBRA as your primary coverage, COBRA may deny claims on the grounds that Medicare should have paid first. You could end up with large unpaid bills.

COBRA and the Special Enrollment Period: Enrolling in Medicare Part B does not automatically terminate your COBRA coverage. However, if you delay enrolling in Medicare Part B because you have COBRA, you will NOT qualify for a Special Enrollment Period when COBRA ends. COBRA is not considered "employer group health plan coverage based on current employment" under MSP rules. If you miss your Initial Enrollment Period and rely on COBRA, you may face a permanent Part B late enrollment penalty.

For a detailed explanation of enrollment windows and how to avoid penalties, see our guide to how to enroll in Medicare.

Workers compensation insurance covers medical expenses and lost wages for job-related injuries and illnesses. Under MSP rules, workers compensation is always the primary payer for work-related injuries. Medicare does not cover services that workers compensation is obligated to pay.

Conditional payments: In some cases, Medicare will make a conditional payment while a workers compensation claim is being processed or disputed. This is not a gift. Medicare will seek full reimbursement from any workers compensation settlement or award. If you receive a workers compensation settlement, you are legally required to repay Medicare for any conditional payments it made related to the injury.

Medicare Set-Asides (MSAs): When a workers compensation case settles and the injured worker is a Medicare beneficiary (or is expected to become one within 30 months), CMS may require a Workers Compensation Medicare Set-Aside Arrangement (WCMSA). This is a portion of the settlement set aside in a dedicated account to pay for future medical expenses related to the injury that Medicare would otherwise cover. The funds must be spent on injury-related care before Medicare will pay.

Reporting requirements: Insurers and self-insured employers are required to report workers compensation settlements involving Medicare beneficiaries to CMS through the Section 111 mandatory reporting system.

No-fault auto insurance (also called personal injury protection or PIP) and liability insurance are both primary to Medicare under MSP rules.

No-fault auto insurance: If you are injured in an auto accident and your state requires no-fault insurance, that insurance pays first for your medical expenses up to the policy limit. Medicare pays second after the no-fault coverage is exhausted. If Medicare makes conditional payments while the no-fault claim is pending, it will seek reimbursement from any settlement.

Liability insurance: If you are injured due to someone else's negligence (a slip and fall, a car accident where the other driver is at fault, a defective product), the at-fault party's liability insurance is primary to Medicare. This is true even if the liability insurer disputes the claim.

Medicare liens on settlements: This is one of the most important MSP concepts for anyone involved in personal injury litigation. If Medicare paid for any medical treatment related to your injury, Medicare has a legal right to recover those payments from your settlement proceeds. This right is called a Medicare lien. Before you finalize any personal injury settlement, you must contact the Medicare Benefits Coordination and Recovery Center (BCRC) to determine whether Medicare has a lien and how much must be repaid.

Failure to satisfy a Medicare lien can result in Medicare pursuing recovery directly from you, your attorney, or the liability insurer. Attorneys who handle personal injury cases involving Medicare beneficiaries have an obligation to protect and satisfy Medicare's interests as part of the settlement process.

Patients with End-Stage Renal Disease (ESRD) who are covered by an employer group health plan face a unique MSP coordination period.

During the first 30 months after Medicare eligibility begins due to ESRD (called the coordination period), the employer group health plan is the primary payer and Medicare is secondary, regardless of employer size. After the 30-month coordination period ends, Medicare becomes the primary payer.

This rule applies even to large employers with 20 or more employees. The ESRD coordination period is a specific exception to the general employer size rule.

Practical implications: If you have ESRD and employer coverage, your employer plan must continue to cover dialysis and related services as the primary payer during the 30-month coordination period. Some employer plans attempt to steer ESRD patients toward Medicare prematurely. This is prohibited under MSP rules, and CMS actively enforces against employers and insurers who violate this requirement.

People under 65 who qualify for Medicare due to disability (after 24 months of Social Security Disability Insurance) face MSP rules similar to the working aged rules, but with a different employer size threshold.

For disabled Medicare beneficiaries under 65, the employer group health plan is primary if the employer has 100 or more employees (or is part of a multi-employer plan with at least one employer with 100 or more employees). Medicare is primary if the employer has fewer than 100 employees.

If you are under 65, on Medicare due to disability, and your employer has fewer than 100 employees, Medicare is your primary payer. You should not delay enrolling in Medicare Part B in this situation.

Veterans Administration (VA) benefits and Medicare operate under a fundamentally different framework than the other MSP scenarios. VA benefits and Medicare do not coordinate with each other in the traditional primary/secondary sense.

The basic rule: VA benefits cover care provided at VA facilities. Medicare covers care provided at non-VA facilities. Generally, you cannot use both for the same service at the same time.

Why enroll in Medicare if you have VA benefits? VA benefits do not protect you from Medicare late enrollment penalties. If you delay enrolling in Medicare Part B because you have VA benefits and later need non-VA care, you will face a permanent late enrollment penalty of 10% per year for every year you delayed. Additionally, VA benefits can change, and having Medicare as a backup ensures you have coverage at non-VA facilities without penalty.

For veterans approaching 65, the decision of whether to enroll in Medicare Part B alongside VA benefits is one of the most common questions our specialists address. Schedule a free consultation to review your specific situation.

When another insurer is the primary payer but has not yet paid (for example, because a liability claim is in dispute), Medicare may make a conditional payment to ensure you receive timely care. A conditional payment is not a permanent payment. It is a loan that Medicare expects to be repaid once the primary payer settles.

How the recovery process works:

The Medicare Secondary Payer Recovery Portal (MSPRP) at cob.cms.hhs.gov/MSPRP allows beneficiaries and their representatives to manage conditional payment cases online, view payment amounts, and submit disputes.

Understanding MSP rules is directly relevant to one of the most consequential decisions Medicare-eligible people face: when to enroll in Medicare Part B.

The general rule is that you can safely delay Part B enrollment without penalty only if you have employer group health plan coverage based on your own or your spouse's current active employment, and the employer has 20 or more employees (or 100 or more if you are under 65 and disabled).

Coverage that does NOT protect you from late enrollment penalties:

If you are relying on any of the above as a reason to delay Part B enrollment, you may be making a costly mistake. The Part B late enrollment penalty is 10% of the standard premium for every 12-month period you were eligible but did not enroll, and it lasts for life.

For a full explanation of how Original Medicare and Medicare Advantage interact with other coverage, and to understand your specific enrollment window, our specialists can walk you through every scenario at no cost.