When you have other insurance (like employer group health coverage), there are rules that decide whether Medicare or your other insurance pays first. The insurance that pays first is called the “primary payer” and pays up to the limits of its coverage. The one that pays second, called the “secondary payer,” only pays if there are costs left uncovered by the primary coverage.
If your other coverage is from an employer or union group health plan, these rules apply:
If you are retired, Medicare pays first.
If your group health plan coverage is based on your or a family member’s current employment, who pays first depends on your age, the size of the employer, and whether you have Medicare based on age, disability, or End‑Stage Renal Disease (ESRD):
— If you are under age 65 and disabled, your plan pays first if the employer has 100 or more employees or at least one employer in a multiple employer plan has more than 100 employees.
— If you are over age 65 and still working, your plan pays first if the employer has 20 or more employees or at least one employer in a multiple employer plan has more than 20 employees.
If you have Medicare because you have ESRD, your plan pays first for the first 30 months you have Medicare.
The following types of coverage usually pay first:
No-fault insurance (including automobile insurance)
Liability (including automobile insurance)
Black lung benefits
Medicaid and TRICARE never pay first. They only pay after Medicare, employer group health plans, and/or Medigap have paid.