Top 10 Reasons Claims Get Denied and How to Prevent Each One

Published April 4, 2026 · 12 min read · By Yagnesh Dave

Every denied claim costs staff time to rework, and some never get paid at all. The good news: most denials come from a short list of causes that a practice can prevent with the right processes in place.

At RCMAXIS, we work every client toward an initial denial rate under 5%, well below the 8-12% industry average. Here's exactly how we do it, organized by the top 10 denial reasons we see across specialty practices.

1. Missing or Invalid Patient Information (Denial Code CO-4)

Incorrect patient demographics remain the single most common cause of claim denials. According to the American Medical Association (AMA), 50% of denials stem from front-end errors including missing or inaccurate data including misspelled names, wrong dates of birth, incorrect insurance ID numbers, and mismatched subscriber relationships.

Prevention Strategy

• Implement real-time eligibility verification at scheduling and check-in
• Use automated demographic verification tools integrated with your EHR system
• Train front-desk staff to verify insurance cards at every visit, not just new patients
• Cross-reference patient information against the 270/271 eligibility response before claim submission

2. Prior Authorization Not Obtained (Denial Code CO-197)

Prior authorization requirements have grown, and denials tied to them are most common for mental health services, advanced imaging, and specialty procedures. This is especially problematic for behavioral health practices where nearly every session beyond the initial evaluation may require authorization.

Prevention Strategy

• Build prior auth requirements into your scheduling workflow
• Maintain a payer-specific authorization matrix updated monthly
• Automate auth tracking with expiration alerts 7 days before deadline
• Document all authorization numbers on the claim at time of submission

3. Duplicate Claims (Denial Code CO-18)

Duplicate submissions are a common denial cause. They occur when practices resubmit claims before the original has been adjudicated, or when both the provider and billing company submit simultaneously during a billing transition.

Prevention Strategy

• Implement a 14-day hold before resubmitting any claim
• Use claim status inquiry (276/277) to check adjudication status before resubmission
• Establish clear submission ownership during billing company transitions

4. Coding Errors and Mismatches (Denial Codes CO-11, CO-97)

Incorrect CPT, ICD-10, or modifier usage is one of the most common denial causes. Common errors include diagnosis-procedure mismatches, unbundling, upcoding, and missing modifiers for bilateral procedures or distinct services.

Prevention Strategy

• Use certified coders with specialty-specific credentials (CPC, CCS, CCS-P)
• Implement pre-submission claim scrubbing with CCI edit checks
• Conduct quarterly coding audits with a minimum 10% chart sample
• Stay current with annual CPT code updates and LCD/NCD changes

5. Timely Filing Violations (Denial Code CO-29)

Each payer has different filing deadlines ranging from 90 days to 365 days from date of service. Medicare requires submission within 12 months, but many commercial payers enforce 90-day windows. Timely filing denials are entirely preventable revenue loss.

Prevention Strategy

• Submit all claims within 24-48 hours of charge entry
• Maintain a payer-specific filing deadline matrix
• Set automated alerts at 50% and 75% of each payers filing limit
• Track claim age in your analytics dashboard

6. Non-Covered Services (Denial Code CO-96)

Services deemed not medically necessary or excluded from the patients benefit plan generate roughly 8% of denials. This is prevalent in specialty clinics performing procedures that require specific diagnosis support or payer-defined frequency limits.

Prevention Strategy

• Verify coverage and benefits before scheduling procedures
• Check LCD/NCD coverage requirements against documented diagnoses
• Implement Advance Beneficiary Notices (ABNs) for Medicare patients when coverage is uncertain

7. Coordination of Benefits (COB) Issues (Denial Code CO-22)

When patients have multiple insurance plans, incorrect primary/secondary designation causes approximately 6% of denials. The birthday rule, COBRA status, and Medicare Secondary Payer rules create complexity that front-desk staff often mishandle.

Prevention Strategy

• Verify COB at every visit, not just new patient registration
• Implement automated COB detection through eligibility responses
• Train staff on the birthday rule and common COB scenarios

8. Out-of-Network Denials (Denial Code CO-151)

Network status denials have increased as payer networks narrow. Verify each patient's network status before the visit, not after the denial.

Prevention Strategy

• Maintain current credentialing across all payers through proactive enrollment management
• Verify in-network status during eligibility checks, not just active coverage
• Alert patients to out-of-network status before rendering services

9. Bundling and Unbundling Errors (Denial Code CO-97)

Incorrect unbundling of services that should be billed together, or failure to append appropriate modifiers, causes significant denials in surgical and procedural specialties. Orthopedic and cardiology practices are most affected due to complex bundling rules around global periods and multiple procedure discounts.

Prevention Strategy

• Use NCCI edit checking on every claim before submission
• Ensure coders understand global surgical period rules and modifier 59/X{EPSU} usage
• Review operative reports for distinct procedural steps before adding modifier 59

10. Missing or Invalid Referral (Denial Code CO-15)

Referral-based denials particularly impact specialist practices receiving patients from primary care providers. Missing or expired referrals are a steady source of preventable denials.

Prevention Strategy

• Verify active referral status during scheduling
• Track referral visit counts and expiration dates in your PM system
• Request referral renewals 2 weeks before expiration

Building a Denial Prevention Program

Individual fixes are important, but systematic denial prevention requires a structured program. At RCMAXIS, our claims management approach includes root cause analysis on every denial, automated prevention workflows, and monthly denial trend reporting for each provider.

The ROI is clear: for a 10-provider practice with $5M annual revenue, cutting denials from the 12% industry average to a 5% best-practice rate puts roughly $350,000 a year of revenue back in play. Not every denied claim is lost for good, but every one costs time and cash flow, and that gap is what a prevention-first process closes. See what this can look like in our illustrative scenarios.

When Denials Turn Into Audits

A denial is a billing problem. A pattern of denials is a compliance signal. Payers and Medicare contractors run their own analytics, and a practice with an unusually high rate of coding-related denials stands out from its peers. The next step can be prepayment review, where your claims are held until someone reads the supporting documentation, which slows cash flow for every claim in the queue, not just the ones with problems. A 3-year lookback with even a modest error rate can turn a small per-claim gap into a sizable repayment demand, which is why a quarterly self-check is worth the time.

If a contractor sends you an additional documentation request, plan on a short window. For Medicare contractors it's typically 45 days to respond, and a late or incomplete response usually means the claim is denied. That's why the fixes in this article, especially clean front-end data and coding checks before submission, protect you twice: they cut denials now and they keep you out of the audit conversation later.

Turn the Top 10 Into a Monthly Scorecard

Take the ten denial categories in this article and build a one-page scorecard. For each, show the number of denials last month, the dollar value, and the trend. Assign an owner to each category and ask them to report on what they changed and what happened.

After a few months you'll see which fixes work and which don't. It also makes denial prevention a shared responsibility, not a billing office problem.

Denial Prevention Checklist

Frequently Asked Questions About Claim Denials

What's the most common cause of claim denials?

According to the article, front-end errors lead the list. It cites the AMA figure that about half of denials come from missing or inaccurate registration data, which is why demographic and eligibility checks before the visit come first.

How long do you have to file a claim before timely filing denies it?

It depends on the payer. Medicare's limit is 12 months from the date of service, while many commercial payers enforce windows as short as 90 days, so the filing deadline for each contract should sit in your billing system, not in someone's memory.

Should you resubmit a denied claim or file an appeal?

It depends on the reason. A correctable error, like a missing modifier or bad demographic, usually calls for a corrected claim. A denial where you believe the payer applied its policy incorrectly calls for an appeal with supporting documentation.