One of them is invisible to your denial dashboard — and your billing team cannot fix it.
The short answer
Most claim denials trace to eight causes: incomplete or noncompliant coding, missing information, untimely filing, inaccurate patient information, missing prior authorization, upcoding or unbundling, duplicate submissions, and provider enrollment gaps.
The last one is the one almost nobody counts. It is also the only category on this list your billing team cannot fix. The claim is clean. The coding is correct. The patient is eligible. The provider’s status with the payer is the problem, and that lives in a different department entirely.
Why this matters to your bottom line
In 2024, insurers offering plans on HealthCare.gov denied 19 percent of in-network claims, according to KFF’s analysis of federal transparency data reported to the Centers for Medicare and Medicaid Services. Insurers received roughly 496 million claims that year. About 85 million in-network claims were denied.
That rate has held near one in five since 2015. It is not a spike. It is the operating environment.
The variation is where the money is. In-network denial rates ranged from 3 percent to 36 percent depending on the insurer. Twenty-six of the 157 reporting insurers denied 25 percent or more. If your payer mix is weighted toward the wrong end of that range, your denial exposure is not average. It is structural.
Fewer than 1 percent of denied claims were appealed. When consumers did appeal, insurers upheld the original decision 66 percent of the time.
What the federal data shows about denial reasons
Here is the finding that should reorganize how you think about denials.
Of the in-network denial reasons insurers reported for 2024, only 5 percent were based on medical necessity. Nine percent were for lack of prior authorization or referral. Administrative reasons accounted for 25 percent — five times the medical necessity share.
| The blind spot, in CMS’s own words CMS defines the administrative denial category as claims that were duplicated, missing information, untimely, or submitted for an unapproved provider. An “unapproved provider” denial is an enrollment denial — and it is bundled inside the second-largest reported denial category, with no separate line of its own. |
The federal data cannot see enrollment denials as a distinct category. Neither can most denial dashboards. That is not a data problem. That is the reason these denials go unmanaged for years.
The 8 most common reasons claims get denied
- 1. Coding is incomplete or does not follow ICD-10. Each diagnosis must follow the ICD-10-CM standard and carry the maximum number of digits for the code in use. Specificity is not a nicety. It is the difference between payment and rework.
- 2. Missing information. Any blank field can trigger a denial. The usual culprits are a missing date of accident, medical emergency or onset.
- 3. The claim was not filed within the allotted time. Your claim can be otherwise perfect. Medicare requires claims within 12 months of the end date of treatment. Commercial carriers set their own windows, and they are shorter. Timely filing denials are almost never recoverable.
- 4. Inaccurate patient information. Name spelling, date of birth, gender, policy number, group number, coverage exclusions. Verify the payer is correct and the policy is active before the visit, not after the denial.
- 5. Prior authorization was missing. Physicians consistently report difficulty determining which tests and procedures require preauthorization. Payer requirements change, differ by plan and leave little room for recovery once the service has been rendered.
- 6. Upcoding or unbundling. Billing for a higher-paying service than the one performed is upcoding. Billing services separately that belong together is unbundling. Both draw denials, and both draw compliance scrutiny.
- 7. The claim is a duplicate. Same treatment, same patient, same provider, submitted twice. This is almost always a workflow defect, not a staff error.
- 8. The provider was not enrolled with the payer. The service was delivered. The documentation is complete. The code is right. The payer has no record of that provider being approved to bill under that tax ID, at that location, on that date. Denied.
The enrollment blind spot
Reasons one through seven are defects on the claim. Fix the defect, resubmit, get paid.
Reason eight is not a defect on the claim. It is a defect in the provider’s status. That difference changes everything about how it behaves.
It is never one claim. It is every claim, for that provider, for that payer, across the entire date range the gap covers. A lapse discovered in week nine is nine weeks of denied encounters.
You cannot appeal it. There is no argument that makes a provider retroactively enrolled. You correct the status and rebill, assuming timely filing has not already closed the window. Often it has.
It is silent. Nobody gets an alert when a revalidation deadline passes. The first signal is denials arriving weeks after the fact, and by then the exposure has compounded.
It is owned outside the revenue cycle. Credentialing and enrollment typically report through medical staff operations or human resources. The denial lands on billing. Billing escalates to a team that does not report to them, has different priorities and had no visibility into the claims that were piling up.
| The governing point You cannot fix a denial category with a team that does not own the input. |
Practice administrator checklist
- Segment your denial report by owner, not just by payer or reason code. If a category routes to a team that cannot resolve it, that category is not being managed.
- Track time to first claim: the days between a provider’s start date and their first successfully adjudicated claim. It is the cleanest measure of enrollment health you can build.
- Build a revalidation calendar with named owners and alerts set 120 days out. Payer recredentialing cycles run two to three years. Staff turnover does not respect them.
- Audit your roster against payer directories quarterly. Tax ID, taxonomy code, service location and group linkage all break silently.
- Start enrollment before the provider’s first day, not after.
- Reconcile denials tagged administrative. Ask specifically how many are provider status, not duplicates. If your system cannot answer, that is the finding.
Frequently asked questions
What are the most common reasons medical claims are denied?
The eight most common are coding errors or ICD-10 noncompliance, missing information, untimely filing, inaccurate patient information, missing prior authorization, upcoding or unbundling, duplicate submissions and provider enrollment gaps. In 2024 federal data, administrative reasons made up 25 percent of in-network denial reasons and medical necessity just 5 percent.
What is a provider enrollment denial?
A provider enrollment denial happens when a payer has no record of a provider being approved to bill under a given tax ID, location and date, even though the claim itself is correct. Because the fix lives in credentialing rather than billing, these denials often affect every claim for that provider until the enrollment gap is closed.
Why are provider enrollment denials so hard to catch?
Federal reporting folds unapproved-provider denials into a broad administrative category alongside duplicates and missing data, so they rarely appear as a distinct line on a denial dashboard. They are also silent: nothing alerts a team when a revalidation deadline passes, so the first signal is denied claims arriving weeks later.
How much revenue do claim denials put at risk?
Insurers denied 19 percent of in-network HealthCare.gov claims in 2024, with rates ranging from 3 to 36 percent by insurer. Fewer than 1 percent of denied claims are appealed, so much of that exposure is never recovered.
The bottom line
Denials are not one problem. They are eight problems, owned by different departments, reported as a single number on a single dashboard, routed to a single team that can only solve some of them.
The organizations that reduce denials meaningfully are the ones that stop asking how many and start asking who owns this.
Advantum Health manages provider enrollment and credentialing and denial management under one accountable team. Not because bundling is tidy, but because the handoff between them is where the revenue disappears.
| Schedule a revenue cycle assessment Find out what your administrative denial bucket is actually made of. Talk with an Advantum denial specialist. |
Sources
KFF, “Claims Denials and Appeals in ACA Marketplace Plans in 2024,” March 24, 2026.
kff.org/patient-consumer-protections/claims-denials-and-appeals-in-aca-marketplace-plans-in-2024
CMS, Transparency in Coverage Public Use File data dictionary (administrative denial category definition).
cms.gov/files/document/transparency-coverage-puf-datadictionary-py25.pdf
CDC, ICD-10-CM.