Medical Billing Errors: How Common Are They in 2026?

Studies show that 26–49% of Medicare claims contain errors, and the Medical Billing Advocates of America estimates that 80% of medical bills have at least one mistake. These errors cost American patients an estimated $210 billion per year. Despite these numbers, only about 20% of patients ever review their bills in detail. Here are the latest statistics on medical billing errors and what they mean for your bill.

1. Key statistics at a glance

The data on medical billing errors comes from federal audits, academic research, and industry analyses. Here are the numbers that matter most:

The takeaway: billing errors are not rare exceptions. They are a structural feature of the American medical billing system — and they overwhelmingly favor the provider, not the patient.

2. The 10 most common billing errors

Not all billing errors are created equal. Some appear frequently but cost relatively little per incident; others are less common but can add thousands of dollars to a single bill. Here are the 10 most common errors, ranked by overall impact (frequency multiplied by average dollar amount):

Error 1: Upcoding — the biggest dollar-impact error

Upcoding is the single most costly billing error for patients. It means your visit or procedure was billed at a higher complexity level than the care you actually received. The most common example is ER visit level coding:

A Health Affairs analysis found that ER visit-level distributions have shifted dramatically upward over the past decade, with Level 4 and Level 5 visits now comprising the majority of ER claims — even as patient acuity has not changed proportionally. The result: patients are systematically billed at higher rates than their care warrants. If you visited the ER for a straightforward issue (sprained ankle, minor laceration, UTI) and were billed at Level 4 or 5, request a coding review.

Error 2: Duplicate charges — the most frequent error

Duplicate charges are the error type patients encounter most often, especially on multi-day inpatient stays. They happen when different hospital departments independently log the same service: the lab bills a CBC and the floor nurse’s charting system also generates a CBC charge for the same day. IV medications, daily labs, and routine supplies are the most frequently duplicated items. Sorting your itemized bill by date and CPT code makes duplicates immediately visible.

Error 3: Unbundling — hidden overcharges in procedure bills

Unbundling inflates your bill by breaking a single procedure into its component parts and billing each one separately. CMS publishes over 200,000 NCCI code pairs specifically to prevent this. A common example: a colonoscopy with biopsy should be billed as CPT 45380 (Medicare rate: $198), but unbundling would bill the colonoscopy and biopsy as separate line items with separate charges totaling more than the bundled rate. BillKarma’s analyzer checks every bill against the NCCI edit list automatically. Learn more about unbundling and other common hospital billing errors in our hospital billing errors guide.

3. Error rates by care type

Billing error rates vary significantly depending on the type of care. More complex encounters generate more line items, more codes, and more opportunities for mistakes. Here is how error rates break down by care setting:

Emergency room bills have the highest error rate for two reasons. First, ER visits involve rapid, multi-provider care with documentation completed after the fact — which increases coding mistakes. Second, ER visit level coding (CPT 99281–99285) is subjective and hospitals have financial incentives to code at the highest defensible level. A JAMA study found that ER visit coding distributions have shifted significantly toward higher levels over the past decade, suggesting systematic upcoding rather than truly sicker patients.

Surgical bills carry the second-highest risk because of the sheer number of billable components: the surgeon’s professional fee, the anesthesia fee, the facility fee, individual supply charges, recovery room charges, and post-operative care. Each component is an opportunity for an error — or an opportunity to unbundle what should be a single charge into several.

4. Who catches billing errors

The short answer: almost no one. That’s what makes billing errors so profitable for the system.

According to AARP and KFF consumer surveys, only about 20% of patients review their medical bills in detail. The other 80% either pay without reviewing, set up a payment plan without questioning the amount, or ignore the bill entirely. Of the patients who do review their bills:

• ~50% find at least one questionable charge — a line item that doesn’t match their recollection of care, a duplicate, or a charge they can’t identify
• ~30% of those who find errors actually dispute them — the rest don’t know how, don’t have time, or assume the hospital is right
• 60–70% of disputes result in an adjustment — meaning the hospital agrees the charge was wrong or reduces it

Putting those numbers together: out of 100 patients who receive a bill with an error, roughly 20 review it, 10 find something wrong, 3 dispute it, and 2 get an adjustment. The other 98 pay the incorrect amount. This math explains why the system persists — the expected revenue from billing errors far exceeds the cost of the occasional correction.

5. The financial impact

Billing errors are not just an inconvenience — they are a significant financial burden on American families. Here is what the data shows about real-dollar impact:

The national picture

National health expenditures in the United States exceeded $4.8 trillion in 2024, according to CMS. If even 5% of that spending represents billing errors and improper payments, the annual cost of mistakes is over $240 billion. The HHS OIG’s own estimate of Medicare improper payments alone was $31.5 billion in fiscal year 2025 — and that covers only the federal Medicare program, not commercial insurance or Medicaid.

Case study: ER visit for a child’s broken arm

Case study: knee surgery with duplicate charges

Case study: lab bills after a routine physical

These cases illustrate a pattern: the errors are not random. They consistently result in higher charges, and they are consistently correctable when patients know what to look for. Use our calculator to check the Medicare rate for any CPT code on your bill.

6. How to check your bill for errors

You do not need a professional medical billing advocate to catch most errors. Follow this five-step process:

Step 1: Get your itemized bill

Call the billing department and request an itemized bill with CPT codes. A summary showing only “Lab Services: $1,200” is not enough. You need every individual charge on its own line with the CPT or HCPCS code, date, description, quantity, and dollar amount.

Step 2: Compare to your Explanation of Benefits

Pull up the EOB from your insurance company for the same dates of service. The patient responsibility on the EOB should match what the provider is billing you. If the numbers differ, one of them is wrong. Common discrepancies include the provider not applying insurance adjustments or billing you the full charge before insurance has processed the claim.

Step 3: Look for the obvious errors

Scan the bill for the three easiest-to-spot error types:

• Duplicates: Same CPT code on the same date appearing twice
• Wrong dates: Charges on a date you were not present or had been discharged
• Services you don’t recognize: Consultations, tests, or medications you have no recollection of receiving

Step 4: Check CPT codes against Medicare rates

Look up the Medicare rate for the highest-dollar CPT codes on your bill. While hospitals charge more than Medicare pays, the ratio tells you whether the charge is in a reasonable range. A charge that is 10–15x the Medicare rate is almost always worth questioning. Use our calculator to look up any CPT code instantly.

Step 5: Check for unbundling

If you had a procedure, look for multiple CPT codes from the same clinical area on the same date. These may be component codes that should have been billed as a single bundled code. BillKarma’s analyzer checks your bill against the CMS NCCI edit list automatically, or you can search the CMS NCCI tools page directly.

7. What happens when you dispute

Many patients avoid disputing because they assume it won’t work. The data says otherwise.

Success rates

Medical billing advocates report that 60–70% of billing disputes result in an adjustment — either a correction of the error or a reduction in the charge. For specific error types, the success rates are even higher:

Duplicate charges have the highest success rate because they are objectively verifiable — the same service on the same date billed twice is indefensible. Upcoding disputes are harder because visit level coding involves clinical judgment, but hospitals still agree to downgrades more than half the time when patients present specific documentation.

Average savings

Across all error types, the average savings from a successful billing dispute is $800 to $3,000, according to medical billing advocate data. For ER bills specifically, the average is higher — closer to $1,200 to $2,600 — because ER upcoding involves large per-incident dollar amounts.

Timeline

Most billing disputes follow this timeline:

• Day 1: Phone call to the billing department identifying specific errors by line item
• Days 1–10: Simple errors (duplicates, data entry) often resolved on the first call or within 10 business days
• Days 10–30: Coding reviews (upcoding, unbundling) typically take 2–4 weeks for the hospital to complete
• Days 30–60: Written disputes and formal billing reviews, if the phone call did not resolve the issue
• Days 60–90: Escalation to insurance company, state insurance commissioner, or Medicare Administrative Contractor if needed

The key: do not pay the disputed amount while the dispute is open. Ask the billing department to place the disputed charges on hold. Most hospitals will not send an account to collections while a formal billing review is pending.

For a step-by-step guide to the dispute process with letter templates, see our complete guide to disputing a medical bill.

Frequently asked questions

Sources

• HHS Office of Inspector General — Medicare Improper Payment Reporting and Annual Audit Results
• CMS — Medicare Fee-for-Service Improper Payment Rate Data
• JAMA Health Forum — Studies on Medicare Claim Accuracy and Coding Error Prevalence
• Health Affairs — Research on Emergency Department Coding Trends and Upcoding
• CMS — National Health Expenditure (NHE) Data and Projections
• CMS — National Correct Coding Initiative (NCCI) Edits and Code Pair Reference
• AARP — Medical Billing Errors: What Patients Need to Know
• KFF — Americans’ Challenges with Health Care Costs and Medical Billing
• AAPC — Medical Coding and Billing Error Research and Industry Standards
• Medical Billing Advocates of America — Billing Error Rates and Patient Dispute Outcomes