How to Check Medical Bills for Errors

Your medical bill arrived and something feels off. Maybe the total is higher than you expected based on what your insurance said you'd owe. Maybe you were billed for something you don't remember receiving. Or maybe you've just heard that medical billing errors are surprisingly common and you want to verify the bill before you pay it. That instinct is worth following. This guide will show you exactly how to pull your Explanation of Benefits, compare it against your provider bill, identify the most common types of errors, and dispute any mistakes you find — in plain language, without needing a background in medical billing.

Why billing errors happen — and why patients are the only ones who catch them

Medical billing errors are common not because every provider is trying to defraud you, but because the system creates almost no pressure to catch mistakes. Providers bill codes that maximize reimbursement. Insurance companies process whatever the provider submits. Neither party has a strong financial incentive to flag a code that results in a higher patient balance. You are the only person in this chain who benefits from finding the error — and most people simply pay the bill without reviewing it.

Errors range from simple data entry mistakes to systematic coding patterns that consistently result in higher charges. The majority are coding mistakes, not intentional fraud. That distinction matters: when you challenge a billing error, you'll get much further treating it as a correction that needs to be made than as an accusation of wrongdoing. In rare cases where a pattern of intentional overbilling is clear, that can be reported to your state insurance commissioner, but that is not where most patients need to start.

What an Explanation of Benefits is — and how to read it

An Explanation of Benefits, or EOB, is a document your health insurer sends you after a claim is processed. It is not a bill. It is a summary of what your provider billed, what your insurer agreed to pay, and what portion is left for you. Reading it carefully is the first step in catching any error.

Most EOBs are organized in columns. Here is what each one means:

• Service description or procedure code: What was billed, usually listed as a CPT code (explained below) and a brief description like "Office visit, established patient."
• Amount billed: What the provider charged before any negotiation. This is often an inflated "list price" that no one actually pays.
• Allowed amount: The maximum your insurer has agreed to pay for that service under your plan's contract with the provider. This is the number that actually matters.
• Plan paid: What your insurer paid directly to the provider.
• Your responsibility: What you owe, after the plan paid its share. This reflects your deductible, copay, or coinsurance — whichever applies to that service.
• Adjustments or not covered: Amounts written off because they exceeded the allowed amount, or denied because the service isn't covered.

If you're unclear on what deductibles, copays, and coinsurance mean and how they interact, the Decipher guide to deductibles, copays, and coinsurance explains each one and shows how they affect your out-of-pocket cost for any given claim. You need to understand those terms to make sense of the "your responsibility" column on your EOB.

You can access your EOB through your insurer's member portal online. If you're on Medicare, your EOB equivalent is called a Medicare Summary Notice. The CMS uniform glossary defines these and other key insurance terms in plain language.

What CPT codes are and why they matter

Every medical procedure, office visit, lab test, and imaging study is assigned a five-digit number called a CPT code — Current Procedural Terminology. These codes are maintained by the American Medical Association and used across every insurer and government program. The CPT code is what determines how the service is priced and whether it's covered under your plan. It is the core of every medical bill.

For example, a routine office visit with a new patient might be billed as CPT 99203 (moderate complexity) or 99205 (high complexity). Those two codes can differ by $100 or more in allowed cost. If you came in for a basic problem and were billed at 99205, that may be a coding error called upcoding — described in the next section.

You can look up any CPT code using the CMS coding and billing resource page. Plain-language lookup tools are also available through CMS's Medicare Physician Fee Schedule, which lets you search a code and see what Medicare considers the appropriate reimbursement for that service in your geographic area. If the code on your EOB doesn't match the procedure you actually received, that discrepancy is worth challenging.

The most common billing errors to look for

Upcoding

Upcoding means a simpler, lower-cost procedure is billed using the code for a more complex, higher-cost one. A common real-world example: a simple tooth extraction (CPT D7140) coded as a surgical extraction (CPT D7210), which can cost two to three times as much. Another: a brief follow-up office visit coded as a comprehensive evaluation. Upcoding is the most financially significant error for patients and one of the most common.

Wrong facility type

Where a service is performed affects how much you pay. If you received care at a clinic that is affiliated with a hospital system, that location may be classified as a hospital outpatient department rather than an independent physician's office. That distinction can trigger your hospital deductible or a higher coinsurance rate — even if you sat in what looked like a normal doctor's office. If your EOB shows a hospital facility code for a visit you thought was an ordinary office appointment, the Decipher guide to surprise medical bills explains how this happens and what you can do about it.

Wrong insurance billed

Some procedures cross coverage lines. Certain oral surgeries, for example, have a legitimate medical coverage component — a jaw fracture repair may be covered under your medical plan even though it was performed by a dentist. If the provider only billed your dental insurance, you may have overpaid because the medical plan would have covered a larger portion. The reverse also happens. Ask providers whether a procedure could be covered under either plan before paying.

Inpatient vs. outpatient status

Whether you are formally admitted to a hospital as an "inpatient" or kept under "observation status" (technically outpatient) dramatically affects what you owe. Under Medicare and most private plans, observation status means higher out-of-pocket costs for the same hospital stay. This is a billing classification made by the hospital, not your doctor — and it is worth verifying before assuming the bill is correct.

Duplicate billing

The same service billed twice, on the same date of service or across two bills from the same provider. This often appears when a provider submits a claim, doesn't see payment quickly, and submits again. Compare every line item on your itemized bill against your EOB and flag identical service codes on the same date.

Unbundling

Some procedures are meant to be billed together as a package, with a single combined price. Unbundling means each component of that package is billed separately — at a combined total that exceeds what the bundled code would cost. For example, a surgical procedure and a routine service performed at the same time that should be one code might be split into multiple codes. CMS has rules called NCCI edits (National Correct Coding Initiative) that govern which codes must be bundled, but patients can identify obvious cases by flagging multiple line items for the same service date that relate to a single procedure.

How to check your bill: a step-by-step process

Here is a concrete scenario. Suppose you had an outpatient procedure and received a bill for $1,400. Your EOB shows an allowed amount of $900, your plan paid $600, and your responsibility is listed as $300. That math seems off — you have a $500 deductible and thought you had already met $400 of it. Here is how to work through it.

1. Request the itemized bill from your provider. Not the one-page summary statement. The full itemized bill lists every charge as a separate line item with the CPT code, the date of service, and the amount billed for that specific item. You are entitled to this and providers are required to provide it. Call the billing department and ask for it by name.
2. Pull your EOB from your insurer's member portal. Match the date of service. You may have multiple EOBs if multiple providers were involved — a surgeon, an anesthesiologist, and a facility may each bill separately for the same procedure.
3. Cross-reference the two documents. Do the CPT codes on the EOB match the services you actually received? Does the facility type (hospital outpatient vs. physician office) match where you were seen? Are there duplicate line items on the same date? Does the "your responsibility" column on the EOB match what the provider is billing you? If the provider is billing you $1,400 but the EOB shows your responsibility as $300, the provider may not have applied the insurance payment correctly.
4. Call the provider billing department first. Most billing errors originate at the provider, so that is where to start. Be specific. Say: "I'm looking at my EOB and I see CPT code 99215 was billed for my visit on [date]. Based on the nature of that visit — a routine follow-up for a controlled condition — I believe the correct code should be 99213. Can you review that with your coding team?" Specificity gets results. Vague complaints about a high bill rarely do.
5. Follow up every call in writing. After you speak with the billing department, send a brief email or letter summarizing what was discussed, what they agreed to review, and the timeline. This creates a record you can reference if the issue escalates.
6. If the provider disputes the error, contact your insurer. Explain that you believe the provider submitted an incorrect CPT code and ask whether you can initiate a formal appeal. Your insurer can request a corrected claim from the provider and reprocess it. Insurers have leverage over providers that individual patients don't. The Decipher guide to appealing a denied insurance claim walks through the formal appeal process step by step.
7. File a formal appeal if needed. Under the Affordable Care Act, you have the right to appeal insurance company decisions. Healthcare.gov explains the appeals process, including your right to an external review by an independent organization if your internal appeal is denied.

What to realistically expect when you challenge an error

Providers correct billing errors more often than most patients expect — especially when the patient is specific about the code in question. A vague complaint ("this seems too high") is easy to dismiss. A specific challenge ("CPT 99215 was applied to a visit that does not meet the documentation requirements for high complexity — I'd like this reviewed") is much harder to ignore, because the person on the other end of the phone knows that insurers audit exactly this kind of thing.

If a corrected claim is submitted to your insurer, your insurer will reprocess it and recalculate what you owe. In straightforward cases — a duplicate billing, an obvious facility type mismatch — this can result in a revised bill within a few weeks. More complex disputes involving coding judgment may take longer, particularly if they go to formal appeal.

The realistic range of outcomes: some errors are corrected immediately and your balance drops. Others require multiple contacts over several weeks. In rare cases, particularly where you believe a pattern of intentional overbilling is occurring, you can report it to your state insurance commissioner or your state attorney general's office. That is outside the scope of most billing corrections, but it is an option if you believe the situation warrants it.

What to do right now

If you have a medical bill in front of you that feels wrong, start with two things: request the itemized bill from the provider and pull your EOB from your insurer's member portal. Put them side by side. Look at every CPT code. Check for duplicates. Check the facility type. Verify that what the provider is asking you to pay matches what the EOB says your responsibility is. If something doesn't line up, you have the information you need to make a specific, informed call to the billing department — and a specific call is one that gets corrected.

Sources: CMS: Uniform Glossary of Health Coverage and Medical Terms, CMS: Medicare Coding and Billing, Healthcare.gov: How to Appeal an Insurance Company Decision