What is Guarantor in Medical Billing? A guarantor in medical billing is the person who is financially responsible for a patient’s medical bills and healthcare expenses. The guarantor may be the patient, a parent, legal guardian, or another individual responsible for payment. For children, a parent or guardian is commonly listed as the guarantor. The guarantor’s information is collected by healthcare providers to help manage billing, insurance claims, and outstanding balances. While the insurance company may cover part of the medical expenses, the guarantor is generally responsible for any remaining amount, including deductibles, copayments, and coinsurance. Accurate guarantor information helps ensure medical billing is processed correctly.