An explanation of benefits (EOB) is the insurance company's written explanation regarding a claim, showing what they paid and what the patient must pay. The document is sometimes accompanied by a benefits check, but it's more typical for the insurer to send payment directly to the medical provider.
The EOB is not a bill, although it will explain any charges that the patient still owes or may have already paid (in the form of a copay at the time the medical care was received, for example). If the patient owes additional money after the insurance company has paid its portion, the medical provider will send a separate bill, which should match the patient's portion listed on the EOB.
