Short answer: When you’re covered by two health plans, coordination-of-benefits (COB) rules decide which pays first (primary) and which pays second (secondary). The secondary plan doesn’t simply double your coverage; together the plans generally pay up to, not beyond, the allowed amount for a service.
Having two plans (say your own and a spouse’s) doesn’t mean double payment. Coordination of benefits determines the order: your own employer’s plan is usually primary for you; for children covered by both parents, the “birthday rule” (the parent whose birthday falls first in the calendar year) often sets the primary plan; and Medicare has its own Medicare Secondary Payer rules.
The primary plan pays first as if it were the only coverage. The secondary plan may then pick up some remaining cost-sharing, but the combined payment generally won’t exceed the total allowed amount, so the second plan fills gaps rather than paying a second full benefit.
Sources
- NAIC Coordination of Benefits model regulation; plan terms; Employee Benefits KB (Coverage Mechanics).
Content history
Originally published: June 16, 2026
Last reviewed: June 16, 2026