How to dispute a medical bill (and win)

In a 2024 Commonwealth Fund survey, about 45% of insured adults were billed for a service they believed should have been covered. Yet according to KFF, fewer than 1% of denied claims in the ACA marketplace were ever appealed. The gap is not because disputes don't work — it's because most people don't know the steps.

Step 1 — Request an itemized bill

Ask the provider for an itemized bill (sometimes called a “UB-04” for hospitals, or a CMS-1500 for professional services) that lists every CPT, HCPCS, and ICD-10 code with the billed amount. A summary statement is not enough — errors hide in the individual line items. You have a right to ask for this; providers generally send it within 30 days.

Step 2 — Get the Explanation of Benefits (EOB)

Your insurer sends an EOB for every claim. It shows what the provider billed, what the insurer allowed, what they paid, and what you owe. Line up the EOB against the itemized bill. If the provider is charging you for something the insurer marked as “plan responsibility” or covered in-network, that is a balance-billing issue (see below).

Step 3 — Check for the big seven error patterns

Before writing, audit the bill for:

• Duplicate charges — same code twice on the same date
• Upcoding — a level-5 CPT used where level-2 or 3 applied
• Unbundling — package services split into expensive line items
• Balance billing after in-network emergency care
• Services not rendered — check against discharge notes
• Wrong modifiers — -25, -59, -50 change reimbursement a lot
• Charges above fair market — compare to Medicare or Healthcare Bluebook

Step 4 — Write the dispute letter

Send a written dispute — email or certified mail — to both the provider's billing department and your insurer. Include:

1. Your account number, date of service, and patient details
2. A numbered list of the specific line items you're disputing
3. The reason for each dispute (“duplicate charge”, “service not rendered”, “balance billing in violation of the No Surprises Act”)
4. A request that the account be placed on hold and not reported to credit bureaus or sent to collections while the dispute is open
5. A deadline (30 days is standard)

Step 5 — Cite the right law

The federal No Surprises Act (effective January 1, 2022) prohibits balance billing for most emergency services, non-emergency services at in-network facilities, and air ambulance services. Uninsured or self-pay patients are entitled to a Good Faith Estimate before scheduled care, and may dispute the final bill with HHS if it exceeds the estimate by more than $400. If a third-party debt collector contacts you, the Fair Debt Collection Practices Act gives you 30 days to request written validation of the debt.

Step 6 — Escalate

If the provider doesn't respond within 30 days, you have options:

• File a complaint with your state insurance commissioner (for insurance-side issues) or state attorney general (for provider billing practices)
• File a federal complaint for No Surprises Act violations at cms.gov/nosurprises or call 1-800-985-3059
• Submit a complaint to the Consumer Financial Protection Bureau for collection-related problems
• Consider a medical billing advocate or consumer attorney for large bills

This article is decision-support content, not legal or medical advice. Consult a licensed professional for your specific situation.