What are the most common billing errors in healthcare?

Six error categories cover most clinic billing problems. Eligibility verification failures: not confirming coverage at booking and check-in causes 27 percent of denials per Change Healthcare. Missing prior authorization: especially common for imaging, DME, injections, and specialty drugs, often unrecoverable once service is delivered. Modifier errors: incorrect use of modifier 25 (separately identifiable E/M), modifier 59 (distinct procedural service), and modifier 51 (multiple procedures) trigger denials and audit takebacks. Upcoding and downcoding: billing higher or lower than documented level of service creates compliance risk (upcoding) or revenue loss (downcoding); both common when documentation does not match billed code. Medical necessity documentation: claims paid then audited and recouped because clinical notes do not support medical necessity per payer LCD/NCD policies. Timely filing failures: each payer has specific deadlines (typically 90 to 365 days from date of service); missed deadlines convert recoverable revenue to permanent loss. Each error category is preventable with workflow discipline; very few require technology investment. Quarterly self-audits of charts against billed codes are the cheapest single quality control investment in clinic billing.