Medicare Secondary Payer Rules for Employer Coverage
October 27, 2026
Medicare Secondary Payer (MSP) rules decide whether Medicare or your employer's group health plan pays your medical bills first in 2026. The answer depends mainly on the size of the employer providing your group health plan and whether you're actively working, not on your age or how long you've had Medicare. Getting this order wrong can lead both plans to deny a claim or leave you with an unexpected bill, so it's worth knowing the rule before you need it.
Quick Answer
If your employer (or your spouse's employer) has 20 or more employees and you're covered through current active employment, the employer group health plan pays first and Medicare pays second. If the employer has fewer than 20 employees, Medicare usually pays first. Different thresholds apply for Medicare based on disability (100 employees) and for End-Stage Renal Disease, which has its own 30-month coordination period regardless of employer size.
The 20-Employee Rule for Active Workers
The Centers for Medicare & Medicaid Services (CMS) classifies an employer's health plan as a group health plan (GHP), a plan sponsored by an employer or employee organization that provides coverage to active workers and their families. Under the Medicare.gov guidance on who pays first, if that employer has 20 or more employees, federal law treats the employer plan as primary for workers who are 65 or older and still actively employed. Medicare becomes the secondary payer, covering costs the employer plan doesn't pick up, as long as those costs are Medicare-covered services.
If the employer has fewer than 20 employees, the order flips: Medicare pays first and the employer plan pays second. This is one reason the timing of your Part B enrollment matters so much when you're weighing Medicare and employer coverage together. If you work for a small employer and delay Part B, you could face gaps, since the employer plan isn't the primary payer and may expect Medicare to cover its share.
Who Pays First by Situation
| Feature | Primary Payer | RecommendedSecondary Payer |
|---|---|---|
| Employer has 20+ employees, you're actively working | Employer plan | Medicare |
| Employer has fewer than 20 employees | Medicare | Employer plan |
| Medicare based on disability, employer has 100+ employees | Employer plan | Medicare |
| Medicare based on disability, employer has fewer than 100 | Medicare | Employer plan |
| End-Stage Renal Disease, first 30 months | Employer plan | Medicare |
| End-Stage Renal Disease, after 30 months | Medicare | Employer plan |
| COBRA continuation coverage | Medicare | COBRA plan |
| Retiree health coverage (not active employment) | Medicare | Retiree plan |
Disability and End-Stage Renal Disease Use Different Thresholds
If you have Medicare based on disability rather than age, the employee threshold for the employer plan to pay first rises to 100 employees. Smaller employers below that count mean Medicare pays first, even though the active-employment relationship is the same as it would be for an older worker.
End-Stage Renal Disease (ESRD), permanent kidney failure requiring dialysis or a transplant, follows a separate rule entirely. According to CMS, during the first 30 months after you become eligible for Medicare due to ESRD, your employer group health plan pays first regardless of employer size. After that 30-month coordination period ends, Medicare becomes the primary payer. Missing this timeline is one of the more common Medicare coverage gaps families run into, since claims submitted under the wrong assumption can be delayed or denied.
COBRA, Retiree Plans, and Medicaid Don't Change the Order
COBRA lets you temporarily keep employer coverage after you leave a job, but it doesn't count as current employment. Medicare pays first over COBRA coverage, no matter how large the former employer was. The same is true for retiree health coverage from a past employer: once you're no longer actively working, Medicare is primary.
Medicaid works differently from employer coverage. When you're enrolled in both Medicare and Medicaid, Medicare always pays first and Medicaid pays last, after any other coverage, including an employer plan, has processed the claim.
Action Checklist Before You Assume an Order
- Ask your employer's benefits office exactly how many employees the company has for MSP purposes
- Confirm whether your coverage is active employment, COBRA, or retiree coverage
- If you have ESRD, note the exact month your 30-month coordination period started and ends
- Review your Part B enrollment timing before relying on a small-employer plan as primary
- Keep a copy of your employer plan's summary of benefits in case a claim is processed in the wrong order
If a Claim Was Paid in the Wrong Order
If Medicare or your employer plan paid a claim as though it were primary when it should have been secondary, contact the Benefits Coordination & Recovery Center (BCRC), the CMS contractor that corrects Medicare's payment records. You can reach the BCRC at 1-855-798-2627. Fixing the record early helps avoid a larger repayment demand later.
Get free help sorting out your coverage order
If you're not sure whether Medicare or your employer plan should be paying first, get plain-language guidance to confirm your situation before a claim goes wrong.
Frequently Asked Questions
A group health plan is coverage an employer or employee organization sponsors for active workers and their dependents. It doesn't include individual market plans, retiree-only plans, or COBRA, which each follow their own payment order rules.
Yes. CMS counts full-time and part-time employees toward the 20-employee threshold. If you're unsure how your employer counts staff, ask the benefits office directly, since the determination affects whether you need Part B right away.
You can often delay Part B without a penalty while covered by a large employer's group health plan through active employment. Review the rules for delaying Part B without a penalty before deciding, since the small-employer exception doesn't apply the same way.
Medicare pays first, your employer plan pays second, and Medicaid pays last as the payer of last resort. This order stays the same whether you qualify for Medicare and Medicaid through income or disability.