US medical billing is handled by humans translating clinical notes into thousands of CPT, ICD-10, and HCPCS codes. Mistakes are common. In a 2024 Commonwealth Fund survey, roughly 45% of insured adults reported being billed for a service they believed should have been covered by their insurance, and about 1 in 5 in-network claims filed on ACA marketplace plans in 2023 were denied according to KFF's analysis. The good news: most errors follow a small number of predictable patterns.
1. Duplicate charges
The same procedure, test, or supply billed twice on the same date. Often the second entry has a slightly different description or code, making it easy to miss on a skim. Ask for an itemized bill (not a summary) and look for identical line items on the same date of service.
2. Upcoding
A more expensive procedure code is used when a cheaper, simpler one applies. The classic example is an emergency-room evaluation-and-management (E/M) code billed at level 5 (CPT 99285 — “high severity, high medical decision-making”) when the clinical picture was actually a level 2 or 3 visit. A single miscoded ER visit can add hundreds or thousands of dollars to a bill.
3. Unbundling
Services that are supposed to be billed together as a single package get split into separate, more expensive line items. Surgical trays, basic lab panels, and routine pre-op testing are common targets.
4. Balance billing
You had insurance, the provider was in-network, but they billed you for the full charge anyway. Since January 1, 2022, the federal No Surprises Act has banned balance billing in most emergency situations and for non-emergency care at in-network facilities. Air ambulance services are covered; ground ambulance services are not yet covered at the federal level.
5. Services not rendered
A procedure, test, or supply appears on the bill that was never actually performed. This can be a clerical mistake (wrong patient chart) or outright fraud. Compare the bill against the discharge notes or your own memory of the visit.
6. Incorrect modifiers
CPT modifiers change how a procedure is reimbursed — for example, indicating that a procedure was performed bilaterally or as a distinct service. Wrong or missing modifiers can silently inflate or deflate the reimbursement, sometimes dramatically.
7. Above fair-market pricing
The billed charge is significantly higher than what the same procedure costs at other facilities in the same area, or what Medicare would reimburse. Medicare rates aren't the last word, but a bill that's 3–10× the Medicare rate is worth a conversation.
What to do if you find an error
- Request an itemized bill with every CPT, HCPCS, and ICD-10 code.
- Match each line against your insurance Explanation of Benefits (EOB) and, where possible, the clinical notes.
- Send a written dispute citing the specific line items and charges you believe to be incorrect.
- If a debt collector contacts you about the account, the federal Fair Debt Collection Practices Act entitles you to written validation of the debt if you request it in writing within 30 days. Disputed debt should not be reported as delinquent while the dispute is open.
Decision-support reminder: Fix My Bill flags potential issues for you to verify with your provider and insurer. It is not a substitute for professional billing review, legal advice, or medical advice.