The 6 Most Common Medical Billing Errors

Updated June 2026 · 10 min read

Medical billing errors are not rare edge cases — they are the rule, not the exception. A 2023 audit by the Department of Health and Human Services found that hospitals incorrectly billed Medicare for billions of dollars in a single year. A study published in the Journal of the American Medical Association found error rates as high as 90% in some hospital billing departments. For patients, this translates to an average overcharge of $1,300 per hospital stay, and in complex cases, tens of thousands of dollars in charges that simply should not exist.

The root cause is structural. The American healthcare billing system relies on a web of over 70,000 ICD-10 diagnosis codes and nearly 10,000 CPT procedure codes. Billers work under high volume and time pressure, often entering codes manually or relying on automated systems that make their own mistakes. Insurance contracts layer negotiated rates on top of chargemaster prices. The result is a system so complex that even experienced billing professionals make consistent, predictable errors — and those errors almost always favor the hospital.

Here are the six most common medical billing errors, how to identify them, and what you can do when you find them on your bill.

1 Duplicate Charges

Duplicate charges occur when the same service is billed twice — sometimes under the same CPT code, and sometimes under two slightly different codes that represent the same underlying service. This is one of the most common errors, and it's often invisible on a summary bill.

A classic example: a patient receives a CT scan of the abdomen. The billing department enters the charge, then a second staff member reviewing the encounter adds it again. The itemized bill shows two line items for CPT 74177 (CT Abdomen and Pelvis with contrast) at $2,400 each. The patient owes $2,400 — not $4,800 — but the summary bill just shows a lump total that hides the duplication entirely.

Duplicate charges are also common for lab work, radiology reads, and anesthesiology time units. Whenever you see the same date of service with what looks like the same service described differently, request clarification before paying.

"In one landmark audit, researchers found that 49 out of 50 hospital bills reviewed contained at least one duplicate charge."

2 Upcoding

Upcoding is the practice — sometimes accidental, sometimes intentional — of billing for a higher-complexity or more expensive version of a service than what was actually performed. It is one of the most costly errors for patients and one of the most difficult to detect without medical knowledge.

The most glaring example involves emergency department visit levels. Emergency visits are billed using CPT codes 99281 through 99285, ranging from minor (Level 1) to severe (Level 5). A Level 5 visit (CPT 99285) can cost $1,200 or more. A Level 3 visit (CPT 99283) might be $200. Patients who came in for a sprained ankle or a minor infection and find CPT 99285 on their bill are almost certainly looking at upcoding.

Upcoding also appears in surgical billing, where a "complex" procedure code is substituted for a "routine" one, or in physician consultation codes, where a brief check-in is billed as an extended evaluation. If the complexity level on your bill doesn't match your memory of what happened — a 5-minute follow-up billed as a 45-minute comprehensive evaluation, for instance — you have grounds to dispute.

3 Phantom Charges

Phantom charges are bills for services you never actually received. Unlike upcoding, which involves a real service billed at the wrong level, phantom charges are simply fabricated — the service is on the bill but never happened.

Common phantom charges include:

• Medications ordered but not administered: A nurse orders a drug "just in case" but never gives it. The charge appears on the bill anyway.
• Specialist consultations that didn't occur: A specialist is listed as seeing you, but you have no memory of the visit — because it didn't happen.
• Physical therapy or rehabilitation sessions: Common in inpatient stays, where sessions are scheduled but canceled without the billing system being updated.
• Recovery room charges for outpatient procedures: Some facilities bill for recovery room use even when the patient was discharged directly from the procedure room.
• Medical equipment you didn't use: Items like crutches, slings, or compression devices billed but never actually provided.

To catch phantom charges, keep a log during your hospital stay. Note every medication you receive, every provider who visits, every procedure performed. Cross-reference your notes against the itemized bill — any charge without a corresponding memory is worth questioning.

4 Unbundling

Unbundling occurs when a hospital breaks apart a procedure that has a single comprehensive billing code — and bills each component individually at a higher combined cost. The practice violates CMS bundling rules and can significantly inflate a patient's bill.

A straightforward example: a comprehensive metabolic panel (CMP) has its own CPT code (80053) and a specific reimbursement rate. Instead of billing the CMP as a single test, an unbundled bill might list each of the 14 individual tests that make up the panel — sodium, potassium, creatinine, glucose, and so on — each with its own charge. The total for the individual codes might be two to three times the cost of the single bundled code.

Unbundling is especially common in surgical billing, where a single operation might involve multiple steps that are supposed to be covered under one surgical code. When you see a long list of procedure codes related to a single surgery, it's worth verifying whether any of those codes should have been bundled. The AMA's CPT Assistant publication and the National Correct Coding Initiative (NCCI) edits published by CMS define which codes must be bundled — your insurer's billing department can often help you cross-check.

5 Out-of-Network Surprise Billing

You chose an in-network hospital. You checked that your surgeon was in-network. Then you receive a bill from an anesthesiologist you never met, who is out-of-network, for $3,800. This is surprise billing — and as of January 1, 2022, it is largely illegal under the federal No Surprises Act.

The No Surprises Act protects patients from unexpected out-of-network bills when:

• You received emergency care at any facility (in-network or not)
• You received non-emergency care at an in-network facility from an out-of-network provider who you did not specifically choose and were not adequately warned about in advance
• Air ambulance services from out-of-network providers are also covered

Under the law, your financial responsibility for these services is capped at your in-network cost-sharing amount — your deductible, copay, or coinsurance. The provider and insurer must resolve the remaining payment between themselves through an independent dispute resolution (IDR) process. If you receive a surprise bill that appears to violate the No Surprises Act, you can file a complaint at cms.gov or call 1-800-985-3059.

Note: the No Surprises Act does not apply to ground ambulance services. This remains an active gap in federal protection, though many states have their own surprise billing laws that cover ground ambulance.

6 Missing Insurance Adjustments

When your insurer has a contract with a hospital, that contract specifies negotiated rates — typically far below the hospital's chargemaster (list) prices. The insurer pays the negotiated rate, and the hospital writes off the difference. You are responsible only for your cost-sharing portion of the negotiated rate, not the list price.

But billing systems sometimes fail to apply these negotiated adjustments. You receive a bill showing the full chargemaster price, or a bill that has partially applied the discount but left a balance that should have been written off. This is a missing insurance adjustment, and it can add hundreds or thousands of dollars to your apparent balance.

The fix: compare your hospital bill to your Explanation of Benefits (EOB) from your insurer. The EOB shows the billed amount, the allowed amount (negotiated rate), the insurer's payment, and your patient responsibility. If the amount the hospital is asking you to pay is higher than what the EOB says your patient responsibility is, contact the hospital billing department and provide a copy of the EOB. In most cases, they will correct the balance once the discrepancy is pointed out.

How to Catch These Errors

Catching medical billing errors requires a systematic approach. Here is a practical checklist:

• Always request an itemized bill. Never accept a summary bill. Every charge should have a CPT code, a description, a date, and an amount.
• Get your Explanation of Benefits. Your EOB from your insurer is your most powerful comparison tool. It shows exactly what your insurer agreed to pay and what your responsibility should be.
• Look up CPT codes. Use the CMS physician fee schedule or the AMA's code lookup to verify that the code on your bill matches the service you believe you received.
• Compare dates and quantities. Check that the number of days billed for room and board matches your actual stay. Check that medication quantities match what you were given.
• Keep notes during your stay. A simple note on your phone listing every provider, procedure, and medication can save you hours of detective work afterward.
• Use ClearBill to automate the review. Our AI scans your itemized bill against known error patterns and flags suspicious charges in seconds, so you don't have to become a medical billing expert yourself.

If you find errors, you have every right to dispute them in writing. Hospitals regularly correct billing errors and reduce or eliminate incorrect charges when patients formally object. The key is knowing what to look for — which you now do.