Common Insurance Billing Errors and How to Dispute Them

Not every denied insurance claim is a coverage dispute. Many are billing errors. A wrong diagnosis code, a typo in the patient ID, a claim submitted to the wrong insurance company, a provider listed as out-of-network when they're actually in-network -- these are not judgment calls by the insurer. They're data entry mistakes that result in denied claims and inflated patient bills. The American Medical Association estimates that one in every seven claims is processed incorrectly, and billing errors account for a significant share of those processing failures.

The difference matters because billing errors are often easier to fix than genuine coverage disputes. A coverage dispute means the insurer reviewed your claim and decided the service isn't covered under your plan. A billing error means the insurer never properly evaluated the claim in the first place because the data was wrong. Fix the data, resubmit the claim, and the payment follows.

This guide covers the most common insurance billing errors, how to identify them on your Explanation of Benefits (EOB), and the specific dispute and appeal processes available to you -- from calling the insurer to filing a formal external review with your state Department of Insurance.

Understanding your Explanation of Benefits

Your Explanation of Benefits (EOB) is not a bill. It's a statement from your insurance company showing how a claim was processed. Every time a healthcare provider submits a claim to your insurer, the insurer sends you an EOB that shows:

• Service date and description. What was done and when. This should match the services you actually received.
• Billed amount. What the provider charged. This is the provider's list price, not what you owe.
• Allowed amount. The maximum amount the insurer will pay for that service based on your plan's contracted rate with the provider. If the provider is in-network, they've agreed to accept this amount as payment in full (minus your cost-sharing).
• Insurance paid. The amount the insurer paid directly to the provider.
• Your responsibility. The amount you owe the provider -- typically a copay, coinsurance, or deductible amount.
• Denial/adjustment codes. If the claim was denied or adjusted, the EOB includes reason codes explaining why. These codes are the key to identifying billing errors.

Compare every EOB to the bill you receive from the provider. The "your responsibility" amount on the EOB should match what the provider is billing you. If the provider bills you more than what the EOB says you owe, that's a billing error -- the provider is charging you more than the insurer's allowed amount, which in-network providers are contractually prohibited from doing (this is called "balance billing").

Keep every EOB. Even if a claim is processed correctly the first time, you may need the EOB later if the provider sends you a bill for a different amount, if you need to verify your deductible accumulation, or if you switch plans and need to prove what was already covered.

Coding errors that trigger denials

Medical claims are processed based on codes -- diagnosis codes (ICD-10), procedure codes (CPT/HCPCS), and modifier codes that provide additional context. If any of these codes are wrong, the claim may be denied even though the service itself is covered by your plan.

Common coding errors

• Wrong diagnosis code. The ICD-10 code submitted on the claim doesn't match the actual diagnosis, or it's not specific enough for the insurer to verify medical necessity. For example, a code for "unspecified back pain" (M54.9) might be denied when the correct code for "lumbar disc degeneration" (M51.36) would be approved.
• Diagnosis-procedure mismatch. The procedure code doesn't logically match the diagnosis code. An MRI of the knee billed with a diagnosis code for headache will be denied because the procedure doesn't match the condition being treated.
• Wrong procedure code. The CPT code for the procedure performed doesn't match what was actually done. This can happen when a similar procedure with a different code is selected by the billing staff, or when a code is updated and the old code is still being used.
• Missing modifier. Modifiers provide additional information about a procedure -- for example, whether it was performed on the left side or the right side, whether it was the initial procedure or a repeat, or whether multiple procedures were performed during the same session. A missing or incorrect modifier can cause a denial.
• Upcoding or unbundling. In some cases, the provider may have used a higher-paying code than appropriate (upcoding) or billed bundled procedures as separate line items (unbundling). These can trigger claim denials or inflated patient costs. Our NCCI Code Pair Checker can verify whether two procedure codes should be billed together.

You can't fix coding errors yourself -- the provider's billing office needs to correct the codes and resubmit the claim. But you can identify that a coding error occurred by reading the denial reason on your EOB. Common denial codes that indicate billing errors (rather than coverage issues) include: "invalid diagnosis code," "diagnosis and procedure mismatch," "duplicate claim," and "missing information."

In-network billed as out-of-network

This error costs patients thousands of dollars. You see an in-network provider at an in-network facility, but the claim is processed as out-of-network -- resulting in a much higher patient cost (higher coinsurance or deductible) and potentially a balance bill for the difference between the provider's charge and the insurer's out-of-network allowed amount.

This happens because:

• Provider's NPI or tax ID is wrong on the claim. Each provider has a unique National Provider Identifier (NPI). If the billing staff submits the claim with the wrong NPI, the insurer can't match the provider to their network contract and processes the claim as out-of-network.
• Provider recently joined the network. There's often a lag between when a provider signs a network contract and when the insurer's claims system is updated. Claims submitted during this lag period may be processed as out-of-network even though the provider has a signed contract.
• Facility is in-network but the provider isn't. You go to an in-network hospital, but the anesthesiologist, radiologist, pathologist, or assistant surgeon is not in the hospital's network. Under the No Surprises Act (effective January 2022), you're protected from surprise balance billing in most of these situations -- but the claim still needs to be processed correctly.
• Wrong plan linked to the provider. Some providers participate in one insurer's PPO network but not their HMO network, or they're in the large group network but not the individual/marketplace network. If your plan is misidentified, the claim goes to the wrong network and is denied.

How to fix it

If a claim is processed as out-of-network and you believe the provider is in-network, call the insurer and ask them to verify the provider's network status as of the date of service. If the provider is confirmed in-network, ask the insurer to reprocess the claim. You may also need to contact the provider's billing office and ask them to verify the NPI and group/tax ID on the claim submission.

For services covered by the No Surprises Act (emergency services, air ambulance, and services by out-of-network providers at in-network facilities), you should not be balance billed regardless of network status. If you receive a balance bill in these situations, file a complaint with the No Surprises Act helpline at 1-800-985-3059 or through CMS at cms.gov/nosurprises.

Duplicate claim processing

Duplicate claims occur when the same service is submitted to the insurer more than once. This can result in duplicate payments (the insurer pays twice and your cost-sharing is counted twice against your deductible), duplicate denials (the insurer denies the second claim as a duplicate, and you're billed for it), or a confusing account balance at the provider's office.

Duplicates happen when:

• The provider's billing office submits the claim, doesn't receive a response within the expected timeframe, and resubmits
• A paper claim and an electronic claim for the same service are both submitted
• The provider corrects and resubmits a claim, but the original claim is also processed
• You have two insurance plans and both process the same claim at the full allowed amount instead of coordinating benefits

To identify duplicate claims, compare your EOBs for the same date of service. If you see two EOBs for the same provider, same date, same service, that's likely a duplicate. Call the insurer and ask them to verify whether the claim was processed twice. If it was, ask for the duplicate to be reversed and your cost-sharing recalculated.

Wrong patient information

Simple data entry errors in patient information are a common cause of claim denials. These include:

• Wrong subscriber ID / member ID. A transposed digit in your insurance ID number causes the claim to be rejected because it can't be matched to your account.
• Name mismatch. Your name on the claim doesn't match your name in the insurer's system. This happens with name changes (marriage, divorce), hyphenated names, suffixes (Jr., III), and preferred names vs. legal names.
• Wrong date of birth. Another common data entry error that prevents the claim from matching your account.
• Wrong group number. If your employer changed insurance plans or group numbers, the provider may still have the old group number on file. Claims submitted with the old group number will be denied.
• Inactive coverage. Your insurance was active on the date of service, but the insurer's system shows it as inactive -- either because of a retroactive cancellation, a COBRA timing issue, or a system error during open enrollment.

Patient information errors are straightforward to fix: identify the incorrect field, provide the correct information to the provider's billing office, and ask them to resubmit the claim. If the denial was due to a system error on the insurer's side (like an incorrect coverage termination date), call the insurer directly and ask them to correct the eligibility record and reprocess the claim.

Coordination of benefits errors

If you have two insurance plans (for example, your own employer plan plus your spouse's plan), the two insurers must coordinate benefits to determine which plan pays first (primary) and which pays second (secondary). Coordination of benefits (COB) errors are among the most common and most expensive insurance billing errors.

Common COB errors

• Wrong primary/secondary designation. COB rules determine which plan is primary based on factors like the "birthday rule" (for dependent children), employment status, and whether the coverage is through COBRA. If the primary/secondary designation is wrong, both claims will be processed incorrectly -- the secondary plan may deny the claim because it thinks it's primary and should have been billed first.
• Both plans deny as secondary. Each plan thinks it's the secondary payer and denies the claim, waiting for the other plan to pay first. The patient gets stuck with the full bill.
• Double cost-sharing. Both plans apply their respective deductibles and coinsurance without accounting for the other plan's payment. The result is that you pay more in cost-sharing than you would with a single plan.
• Outdated COB information. You used to have two plans but dropped one. The insurer's system still shows the old secondary coverage and denies claims pending COB from a plan that no longer exists.

How to fix COB errors

Call each insurer and verify the primary/secondary designation. If it's wrong, ask the insurer to update it and reprocess denied claims. You may need to fill out a COB questionnaire (most insurers send these annually). Make sure the information is current -- report any changes in coverage promptly to avoid future COB errors.

Deductible and cost-sharing errors

Your cost-sharing (deductible, copay, coinsurance, and out-of-pocket maximum) is calculated by the insurer's claims system based on your plan's benefit design and your year-to-date accumulations. Errors in this calculation directly affect how much you pay.

• Deductible not applied correctly. If you've already met your deductible but a claim is processed as though you haven't, you'll be billed for costs that should be covered. This can happen when claims are processed out of order, when a claim from earlier in the year is reprocessed, or when there's a lag in updating your accumulations.
• Out-of-pocket maximum exceeded. Once you've hit your annual out-of-pocket maximum, the insurer should pay 100% of covered services. If you're still being charged cost-sharing after hitting the max, the insurer's system has an accumulation error. Check your EOBs and add up all the cost-sharing amounts. If the total exceeds your plan's out-of-pocket maximum, call the insurer immediately.
• Wrong cost-sharing tier. If your plan has different cost-sharing for different tiers of providers or services (e.g., lower copay for primary care vs. specialist, different coinsurance for generic vs. brand-name drugs), the wrong tier may have been applied. Check the EOB's benefit tier against what your plan documents say for that type of service.
• Preventive care charged cost-sharing. Under the Affordable Care Act, most health plans must cover certain preventive services with no cost-sharing (no copay, no coinsurance, no deductible). If you received a covered preventive service (annual physical, mammogram, colonoscopy, immunizations, etc.) and were charged cost-sharing, the claim may have been coded incorrectly (missing the preventive care diagnosis code) or the insurer may have misclassified the service.
• Family vs. individual deductible confusion. Family plans have both individual and family deductibles. Some plans require each family member to meet their individual deductible before benefits kick in for that member; others allow the family deductible to be met by any combination of members. If your plan's rules aren't being applied correctly, your cost-sharing will be wrong.

Keep a running total of your deductible and out-of-pocket spending throughout the year. Your insurer's portal usually shows this, but the numbers may lag by weeks or months. If your calculations don't match the insurer's, call and ask for a detailed accumulation report showing every claim that was counted toward your deductible and out-of-pocket maximum.

Prior authorization billing failures

Many health plans require prior authorization (pre-approval) for certain services -- surgeries, advanced imaging, specialty drugs, inpatient stays, and others. If the prior authorization is not obtained before the service is provided, the insurer may deny the claim -- and the patient may be billed for the full cost.

Prior authorization billing errors include:

• Authorization was obtained but not linked to the claim. The provider got the authorization, but the authorization number wasn't included on the claim submission. The insurer denies for lack of authorization even though it exists. This is a fixable billing error -- the provider needs to resubmit with the authorization number.
• Authorization was for a different date or facility. The authorization specifies a particular date range and/or facility. If the service was delayed or moved to a different location, the original authorization may not apply. The provider should have requested an updated authorization.
• Emergency exception not applied. Emergency services do not require prior authorization under federal law and most state laws. If an emergency service was denied for lack of prior authorization, the insurer made an error.
• Retroactive authorization not requested. Some insurers allow providers to request authorization retroactively (typically within 48-72 hours of the service) in situations where prior authorization wasn't feasible. If this window hasn't passed, the provider can still fix the situation.

If you receive a denial related to prior authorization, contact the provider's billing office first. Ask them to verify whether authorization was obtained and, if so, to resubmit the claim with the authorization number. If the provider didn't get authorization when they should have, the provider -- not you -- should bear the financial responsibility in many cases (this depends on your plan terms and state law).

Internal appeal process

Under the Affordable Care Act, all health plans must provide an internal appeals process for denied claims. You have the right to appeal any denial, and the insurer must conduct a full and fair review of your appeal.

How to file an internal appeal

1. Review the denial reason. Your EOB or denial letter includes the specific reason for denial and instructions for appealing. Read this carefully -- the denial reason determines what information you need to provide in your appeal.
2. File within the deadline. Most plans give you 180 days from the denial date to file an internal appeal. Don't wait -- file promptly.
3. Submit in writing. Send a written appeal letter to the address specified in the denial notice. Include:
   • Your name, member ID, and claim number
   • The date of service and provider name
   • The denial reason (quote it from the EOB)
   • Why the denial is wrong (cite the specific billing error)
   • Supporting documentation (correct codes, provider network verification, authorization records, etc.)
4. Request an expedited review if urgent. If the denial involves a service you need urgently (ongoing treatment, hospital admission), you can request an expedited appeal. The insurer must respond within 72 hours for urgent appeals.

The insurer must make a decision on your internal appeal within 30 days for pre-service claims (services not yet received) and 60 days for post-service claims (services already received). If the appeal involves a billing error (wrong code, wrong patient info, network status error), the resolution is usually straightforward once the correct information is provided.

External review and state DOI complaints

If your internal appeal is denied, you have the right to an external review by an independent third party. This applies to all plans regulated under the ACA (employer plans, marketplace plans, and individual plans).

External review

• You must file for external review within 4 months of the final internal appeal denial.
• An independent review organization (IRO) reviews your claim, the insurer's decision, and any supporting evidence.
• The IRO's decision is binding on the insurer -- if the IRO overturns the denial, the insurer must pay the claim.
• There is no cost to you for the external review in most states.

State Department of Insurance (DOI) complaint

Your state's Department of Insurance (DOI) regulates insurance companies operating in the state and handles consumer complaints. A DOI complaint is appropriate when:

• The insurer isn't following its own appeals process (missed deadlines, didn't respond, didn't provide required information)
• The insurer is engaging in a pattern of incorrectly processing claims (systemic billing errors)
• You believe the insurer is acting in bad faith (denying valid claims without reasonable justification)
• The internal appeal and external review processes haven't resolved the issue

To file a DOI complaint, search for "[your state] department of insurance complaint" and follow the online filing process. You'll need your policy information, the claim details, copies of the denial and your appeal, and the insurer's response.

DOI complaints are effective because insurers are regulated entities that need DOI approval for rate increases, new products, and market entry. A pattern of consumer complaints can trigger a market conduct examination -- a comprehensive audit of the insurer's claims handling practices.

How to protect yourself

These practices will help you catch insurance billing errors before they cost you money:

• Read every EOB. Don't throw them away or ignore them. Compare the service description to what you actually received, verify the allowed amount is reasonable, and check that your cost-sharing is calculated correctly.
• Compare EOBs to provider bills. The amount the provider bills you should match the "patient responsibility" amount on the EOB. If the provider is billing you more, call them and reference the EOB.
• Track your deductible and out-of-pocket spending. Keep a spreadsheet or use your insurer's online portal to monitor your year-to-date accumulations. Flag any claim where the cost-sharing seems wrong.
• Verify your provider's network status before every visit. Don't rely on the provider's staff to verify -- they may not know which networks they participate in. Call your insurer or check the provider directory on your insurer's website.
• Keep records. Save all EOBs, bills, correspondence, prior authorization numbers, and call notes. If you call the insurer or provider, write down the date, time, person's name, and what was discussed.
• Don't pay a disputed bill. If you've identified a billing error and are actively disputing it, don't pay the disputed amount. Pay any undisputed portion, but tell the provider in writing that the remaining amount is under dispute. Most providers will not send a disputed balance to collections while the dispute is active, though practices vary.
• Use our tools. Our CPT/HCPCS Lookup tool can help you verify procedure codes, and our NCCI Code Pair Checker can identify unbundling errors on medical claims.

For a comprehensive overview of medical billing errors beyond insurance processing issues, see our complete guide to medical billing errors. For guidance on reading your medical bill line by line, see our itemized medical bill guide. For the general dispute process, see our universal dispute guide. We also have procedure-specific billing guides for ER visits, colonoscopy, MRI/CT scans, and mental health services -- each of which covers insurance-related issues specific to that procedure. For state-specific protections, see our state billing rights guide.

Disclaimer: This guide is for educational purposes only and does not constitute legal, financial, medical, or professional advice. Insurance laws and regulations vary by state, plan type, and situation. Consult a licensed professional for advice specific to your circumstances.