Coordination of Benefits is the concept that allows you to use multiple insurance plans to pay parts of a bill. Generally, claims are billed to your primary insurance company and that remaining amount is then billed to the secondary insurance company. The total amount paid can not exceed 100% of the cost. You may still be responsible for an amount after both companies have paid their part.

There can be quite a few restrictions regarding COB (Coordination of Benefits), so contacting both companies can help to clarify the situation. Typically you can call and speak to a representative and mention Coordination of Benefits, and they should be able to provide you with more details.