A guarantor on a medical bill is the person who is legally responsible for paying a patient’s healthcare expenses if the insurance company does not cover the full cost or if there is an outstanding balance. The guarantor is often the patient, but it can also be a parent, legal guardian, spouse, or another financially responsible individual, especially when the patient is a minor or dependent. Healthcare providers use the guarantor’s information for billing, payment collection, and communication regarding account balances. Accurate guarantor information is essential in medical billing because it helps ensure bills are sent to the correct person, reduces payment delays, minimizes billing errors, and supports an efficient revenue cycle.