Denials can happen because of a variety of reasons such as wrong or incomplete patient information, missing prior authorizations, duplicate billing, coding mistakes, and more. Some denial issues can be resolved through correction and resubmission. But some require a formal appeal with supporting documentation.

Denials are now more complex in 2026 due to stricter payer audits and continual ICD-10 and CPT code updates. This is why healthcare practices are focusing on submitting accurate claims to reduce delays.

This guide breaks down what a denial is in medical billing, its causes, and solutions. It also discusses how to prevent medical billing denials from happening again.

What Is a Denial in Medical Billing?

A denial in medical billing occurs when an insurance company receives and processes a claim but decides not to pay it, either fully or partially. This can happen due to errors, missing information, or non-compliance with payer policies. 

Denial is different from claim rejection. A rejected claim is not accepted for processing by the payer due to technical or formatting issues. This is often stopped at the clearinghouse or front-end level. 

Rejected claims can be corrected and submitted. Denied claims require further actions, such as submitting accurate information with proper justification and supporting documents.

Why Medical Billing Denials Matter for Your Revenue Cycle

Medical billing denial directly impacts the financial stability and operational cash flow of your healthcare practice. This is because denied claims delay payments, increase administrative workload, and reduce the overall effectiveness of the revenue cycle.

The average cost to rework on a denied claim is $25–$118, depending on its complexity. Most healthcare organizations try to maintain a denial rate below 3%. One of the major problems is that many denied claims are never resubmitted. 

According to AMA data, 78% of denied claims are abandoned instead of being corrected and resubmitted. Many denial claims are left unworked, which leads to revenue leakage for healthcare practices. Even preventable denials can pile up over time and cause financial loss when follow-up is not done properly. 

So, fixing medical billing denials is crucial to improving the revenue cycle of your healthcare practice. 

10 Most Common Medical Billing Denials and How to Fix Them

Every medical billing denial has a specific root cause and a clear fix given below:

1. Incorrect or incomplete patient information

   Incorrect or incomplete patient information is a common error in medical billing, where patient demographics (name, age, contact, date of birth) are incorrect. 

   Common denial codes: CO-4, CO-16

   Reason: When front desk staff enter patient data manually, a patient presents outdated insurance cards, or when unverified eligibility details are submitted for a claim cause incomplete information. 

   How to fix it?

   • Collect and scan the insurance cards of patients on every single
   • Use real-time eligibility verification tools that connect you directly to the payer, instead of solely relying on patient-provided information
   • Add a pre-submission scrubbing step to patient details, like demographic and insurance coverage, to fix any errors before claim submission
   • Track front desk staff dealing with patient demographics so they can be held accountable in case of any issue later

2. Insurance eligibility not verified

   The patient’s insurance coverage is not active, terminated, or changed at the time of service. Claim denied because the patient had no valid benefits on the date of submission. 

   Common denial code: CO-27, CO-15. 

   Reason:  Insurance eligibility issues occur when patient eligibility is checked at the time of scheduling, but not rechecked on the day of service. Insurance coverage can change between the time of booking and actual visit due to changes in the employer plan, medical redeterminations, or policy switches without prior notice. 

   How to fix it?

   • Verify eligibility on the date of service instead of relying on verification done at the time of scheduling
   • Run batch eligibility checks 24-48 hours before the patient’s appointment
   • Document each eligibility check with a timestamp and the payer’s response to maintain a clear audit trail in case of disputes.
   • Train front-desk staff to compare the presented insurance card with the records on file. If anything looks different, report it or fix it before the doctor sees it.

3. Missing or invalid prior authorization

   Performed services required prior authorization, but the healthcare practice missed it, approved for a different service, or the authorization expired before the date of the appointment. 

   Common code denial: CO-15 and CO-197. 

   Reason:  Prior authorization is one of the most critical steps in the modern medical billing workflow process because missing approval often leads to denial. Staff may not realize that a procedure requires approval, or may get approval for the wrong CPT code, or forget to track the expiry of approval. These factors lead to denial. 

   How to fix it?

   • Make sure you have an updated list of payer-specific authorization requirements for the most commonly used procedures and review it constantly.
   • Track authorization expiry dates on your computer and set a reminder of 5-7 days before expiry
   • If there are changes in procedure during treatment, get updated authorization approval for that

4. Inaccurate medical coding (ICD-10 / CPT Errors)

   Inaccurate medical coding occurs due to adding wrong, outdated, or unsupported diagnosis or procedure codes. Common culprits for this are the usage of deleted codes, codes not supported by documentation, or violating CPT bundling rules.

   Common code denial: CO-4, CO-11, and CO-97.

   Reason: Codes such as ICD-10 are updated on October 1st, and CPT codes are updated on January 1st every year. If practices still use outdated codes, the claim is denied automatically. Errors can also occur if vague diagnosis codes are used instead of specific ones. Denials also occur due to incorrectly applied modifiers; CPT codes violate National Correct Coding Initiative (NCCI) edits. It can also happen due to a lack of a diagnosis code to support medical necessity. 

   How to fix it?

   • Update your coding system in the billing software right after the codes are updated, and do not use old code sets
     
   • Run a check for deleted codes in your charge master and superbills before each annual update to remove outdated codes and prevent billing errors
   • Follow the CMS National Correct Coding Initiative (NCCI) guidelines while checking CPT code combinations
   • Codes must be trained and updated on the latest coding rules and guidelines
   • Perform internal code audits on high-volume procedures twice a year to catch any errors early

   Each year, new, changed, and deleted billing codes become effective on October 1st for ICD-10 codes and January 1st for CPT2 (procedure codes). Submitting outdated codes on a claim will result in claim rejections.

5. Duplicate claim submission

   Duplicate claim submission happens when a payer receives the same claim from a patient more than one time. In this situation, more than one submission is denied. Sometimes it happens because the original claim was not updated or corrected before resubmission. 

   Common denial code: CO-18. 

   Reason:  Staff often resend the claim if they do not get a response within the given time. Sometimes “no response” is mistaken for “not received,” which leads to unnecessary resubmissions even though the original claim is still being processed.

   How to fix it?

   • Check the claim status in the payer portal or the clearinghouse before resubmitting.
   • Only resubmit when you get confirmation that your claim was received.
   • If corrections are required, first cancel or delete the existing claim before you submit the new one.

6. Timely filing limit exceeded

   When healthcare practices submit claims after the deadline passes, a medical billing denial can occur. Most commercial insurance payers require claims to be submitted within 90-180 days from the date of service. 

   Common denial code: CO-29. 

   Reason:  Claims can get delayed in the billing process due to missing documents, unsigned orders, or unresolved eligibility issues. Billing staff remains busy fixing issues like coding errors or eligibility issues, and forgets the deadline for claim submission. 

   How to fix it?

   • Keep a proper payer-specific list and update it every year when contracts change
   • Monitor every pending claim and review if there is any claim unresolved for more than 30 days
   • Set system alerts for claims whose deadlines are near so you do not miss them
   • For denied claims, check any exceptions from the payer side and write any reason that caused the delay and was outside your control

7. Lack of medical necessity documentation

   The insurance payer decides that the service billed was not medically necessary based on the clinical documents submitted with the claim or available to support it. 

   Payers typically rely on tools like Local Coverage Determinations (LCDs), National Coverage Determinations (NCDs), and internal utilization review guidelines to assess medical necessity. These tools help them determine whether a service meets coverage and clinical appropriateness standards. 

   Common code denial: CO-50 and CO-167.

   Reason:  The medical notes do not clearly explain why the service was needed. A provider may perform a justified treatment, but if the documentation does not clearly connect the diagnosis with the service in a way that matches payer rules (LCD or NCD criteria), the claim is denied.

   How to fix it?

   • Ensure providers and coders understand payer medical necessity rules (LCD/NCD) for high-risk services. If a case does not clearly meet criteria, the documentation must explain why the service was still needed for that specific patient.
   • Avoid vague notes. Instead of general statements, include clear details like severity, duration, previous treatments tried, and how the condition affects the patient’s daily life.
   • Attach supporting documents such as clinical notes, prior authorization records, and test results when submitting the claim.
   • Use structured documentation templates for services that are commonly denied, so key medical necessity details are consistently captured.

8. Non-covered services or benefit exclusions

   The service is not covered under the patient’s insurance plan benefits. So, the denial here is not due to errors in billing or documentation. 

   Common code denial: CO-96 and CO-26. 

   Reason:  Staff may assume the services are covered as they handle multiple patients, so that services may be covered under other plans, and they get confused. Coverage depends on the coverage plan, the employer group, and the policy year. 

   Also, keep in mind that services like cosmetic procedures, fertility treatments, and some durable medical equipment are often excluded but do not show in the eligibility check, mostly.

   How to fix it?

   • Do not just check the insurance eligibility; get prior authorizations for the required procedures. 
   • Check specific benefit coverage for non-routine high-cost services
   • If there is some confusion in coverage, contact the payer directly and document the confirmation with the representative`s name, date, and reference number.
   • In case the coverage is uncertain, get a form signed by the patient for payments after treatment.
   • For Medicare patients, use an Advance Beneficiary Notice (ABN) when there is doubt about coverage or medical necessity, so financial responsibility is clearly defined in advance.

9. Coordination of Benefits (COB) issues

   OB issues arise when patients have multiple insurance plans, such as primary and secondary. It causes claim delays, denials, and miscommunication on which plan pays first. 

   Common code denial: CO-20, CO-16

   Reason: Patients forget or do not disclose secondary coverage during registration. In some cases, the primary insurance payment details are not included when billing the secondary payer. This issue commonly occurs with Medicare patients who have supplemental insurance or with dependents covered under more than one employer-sponsored health plan.

   How to fix it?

   • Ask every patient whether they have any other insurance plan at the time of registration
   • Must add primary payers’ explanation of benefits (EOB) when you send claims to the secondary payer
   • To know whether Medicare is the primary or secondary, use the Medicare Secondary Payer questionnaire

10. Out-of-network provider denial

    The provider who treated the patient is not part of the patient’s insurance network. Because of this, the insurance company may deny the claim or pay a lower out-of-network rate. Denials can also occur when payer directories are outdated or when provider enrollment has not been fully activated despite completed credentialing.

    Common denial codes: CO-97 and CO-242.

    Reason: Sometimes a provider works at a practice but is not individually enrolled with a patient’s specific insurance plan. This often happens with new providers, temporary providers, or recently hired staff whose credentialing is still pending.

    How to fix it?

    • Keep an updated credentialing tracker showing which providers are enrolled with each insurance payer.
    • Start credentialing new providers immediately and avoid scheduling patients under plans where enrollment is not yet approved.
    • Before billing under a supervising provider, confirm that the payer allows it and follow all compliance rules.
    • For temporary or locum tenens providers, review each payer’s billing and modifier requirements before claim submission.

How to Prevent These Medical Billing Denials from Happening Again

Fixing claim denials becomes easy when you identify the core problems behind them and correct them.

Step 1: Track which denials are repeating

First of all, review the denial codes, payer, provider, and service type to identify the patterns. If the same denial occurs every time, it means there is an issue in the workflow. Track details like:

• Denial code
• Insurance payer
• Date of service
• Date denied
• Root cause category (eligibility, coding, authorization, documentation, or front-desk errors)

When healthcare practices monitor these patterns regularly, it helps them identify recurring issues early. 

Step 2: Fix the root cause instead of repeatedly appealing

Appealing for a denied claim is crucial, but appealing repetitively for the same denial is not a good practice. Identify where the error entered the process and correct it there. Let’s understand it with an example:

• Frequent duplicate claim denials may indicate poor resubmission procedures. 
• Repeated authorization denials may mean that payer authorization requirements are outdated in the workflow. 

Correction in process prevents you from future denials instead of correcting the same claim again and again. 

Step 3: Strengthen front-end verification to stop denials before submission

Many denials in medical billing can be prevented before the claim is submitted. Strong verification processes reduce errors and improve clean claim rates. 

Key checkpoints include:

• Verifying insurance and authorization requirements during scheduling
• Rechecking eligibility before the appointment
• Confirming patient demographics and insurance cards at check-in
• Ensuring documentation supports billed services before claim submission

Spending a few extra minutes on verification can prevent hours of denial-related rework later.

Reducing Medical Billing Denials Starts at the Front Desk

Most medical billing denials start from the front desk.  Errors such as incorrect insurance details and incomplete documentation usually start during scheduling or patient intake. Staff take data in a hurry and enter it manually, which itself is a valid reason for errors. 

Once a claim is denied, fixing it takes more time and requires more money. This is why a clear and front-desk process is needed to avoid medical billing claim denials. Staff need to verify insurance information carefully, check for prior authorization, and ensure all patient details are correct. 

Many healthcare practices are leveraging virtual medical billing assistants to manage insurance certification, payment records, payment tracking, and claim support to avoid denials. When healthcare practices improve these front-end processes, they reduce their revenue loss and improve the overall revenue cycle.