Medicare Secondary Payer (MSP)
Medicare Secondary Payer (MSP) is the set of federal rules that determine when another insurer must pay before Medicare. When a working-aged group health plan, workers compensation, liability, or no-fault coverage applies, that payer is primary and Medicare pays second. Billing Medicare first in these situations produces a denial and a recovery demand.
- What it decides
- Whether Medicare pays first or second
- Common primary payers
- Group health plan, workers comp, liability, no-fault
- Screening tool
- MSP questionnaire at registration
- Wrong order penalty
- Denial and Medicare recovery demand
What is Medicare Secondary Payer?
Medicare Secondary Payer (MSP) is the body of federal law that says Medicare should not pay when another insurer is legally responsible first. It exists to protect the Medicare Trust Fund: if a working-aged patient has employer coverage, that plan pays before Medicare. MSP is the mirror image of Medigap, where Medicare pays first and a supplement pays second.
Determining payer order is a coordination of benefits task, and getting it wrong is expensive on both ends.
Who pays before Medicare?
Several situations put another payer ahead of Medicare:
| Situation | Primary payer |
|---|---|
| Working beneficiary, large-employer group plan | Group health plan |
| Work-related injury | Workers compensation |
| Auto accident | No-fault / auto insurer |
| Third-party liability | Liability insurer |
| First 30 months of ESRD | Group health plan |
Outside these, Medicare is primary and Part B processes first.
How do you bill Medicare in the correct order?
Example: a 68-year-old still working at a 400-employee company has a knee MRI. Medicare is secondary. The biller submits to the employer plan first, receives the primary EOB, then bills Medicare secondary with the primary payment shown. Billing Medicare first would deny and, if paid in error, trigger a recovery demand.
- Run the MSP questionnaire at every registration and update it periodically.
- Verify coverage order through eligibility and the Common Working File.
- Bill the true primary payer first and capture the primary remittance.
- Submit the Medicare secondary claim with the primary payment reflected.
Frequently asked questions
Medicare pays second when another coverage is legally primary: an employer group health plan for a working beneficiary (or spouse) at an employer above the size threshold, workers compensation for a work injury, no-fault or liability insurance after an accident, or the first 30 months of coverage under ESRD rules. In these cases the other payer must be billed first.
The claim denies or, if Medicare paid in error, CMS issues a recovery demand to recoup the payment once it learns another payer was primary. Correcting MSP order after the fact means refunding Medicare and rebilling the true primary, often past that payer's timely filing window. Screening up front prevents the whole mess.
Use the MSP questionnaire at registration to ask about employment, spouse coverage, accidents, and other insurance. Verify through eligibility tools and the Common Working File. Do not assume Medicare is primary just because the patient is 65; a working beneficiary with large-employer coverage has Medicare as secondary.
Sources & further reading
Reviewed by the ImmediCare Solutions RCM team
Certified billers and coders handling claims across 50+ specialties nationwide. This entry is reviewed against current payer policy and CMS rules. Last review: Jul 5, 2026.
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