How do two insurances work?

Some patients carry two insurances: a primary and a secondary. There is a strict order, and it never bends. The primary always pays first.

Only after the primary has answered does the leftover balance go to the second insurance. Responsibility moves. It never sits still. See Who is the guarantor?.

Here is the sequence:

1. The primary answers. Its payment posts to the claim like any other remittance.
2. What the primary did not cover does not fall on the patient yet. It moves to the secondary, and the claim reads ready for secondary.
3. You build the secondary claim. The key rule: it carries the primary’s payment with it. The second insurance has to see what the first one already paid and allowed, so it can pay only the correct remainder.
4. The secondary answers, and its payment lands on the same charge as the primary’s. Two payments, one charge.

When the two together cover the whole allowed amount, the claim comes all the way to zero. Remaining zero, patient owes zero. A fully paid two payer claim really does net to nothing left.

On the secondary’s remittance you will often see OA-23, which is the impact of the prior payer’s decision. That is not a denial. It is the second payer accounting for what the first one already did.

You can always ask the assistant to explain the payer order and it will walk you through who paid what, and why.