Dual coverage sounds like protection. In practice it often creates a coordination battle. Here is how primary and secondary coverage works — and how to fix it when both insurers point at each other.
| Situation | Who Is Primary |
|---|---|
| Adult with own employer plan + spouse's employer plan | Your own employer plan is primary for you. Spouse's plan is secondary for you. |
| Child covered by two parents' plans | Birthday rule: the parent whose birthday falls earlier in the calendar year has the primary plan for the child. |
| Medicare + employer coverage (20+ employees) | Employer plan is primary, Medicare is secondary. |
| Medicare + employer coverage (fewer than 20 employees) | Medicare is primary, employer plan is secondary. |
| Medicare + Medicaid | Medicare is almost always primary. Medicaid is the payer of last resort. |
Submit your claim to the primary insurer first. Once the primary pays and you receive the Explanation of Benefits, submit both the original claim and the primary insurer's EOB to the secondary insurer. The secondary insurer then determines what it will pay on the remainder. If your provider handles billing, they should be submitting claims to both insurers in sequence. Submitting to the secondary first, or both simultaneously, will delay or complicate payment.
