Top Medical Billing Denials in 2026 [86% Are Preventable]

What if the denial code sitting in your inbox right now is one your front desk could have prevented before the patient even left the building?

Most practice owners never ask that question, because most denial codes read like a foreign language. You see a string of letters and numbers on an EOB, shrug, and move on to the next task, while the revenue quietly disappears. Multiply that by a few dozen claims a month, and you’ve got a real leak in your practice’s cash flow, exactly the kind of leak a denial management strategy is built to catch and close before it costs you another month of revenue.

Here’s the good news. Denials aren’t random. Industry-wide data shows the same categories and codes repeating in practice after practice, in every specialty, every month. Once you know where they come from and what each one means, you stop guessing and start fixing.

The most widely cited breakdown of denial categories still traces back to Change Healthcare’s 2020 Revenue Cycle Denial Index (102 million claim remits, $407 billion in charges, across 1,500 U.S. hospitals), which found 86% of denials are potentially avoidable and only 14% are truly unavoidable. Nearly one in four potentially avoidable denials (24%) is never recovered once it happens. It’s still the reference point most 2026 industry analyses cite, including Optum’s own current denial-rate commentary, because no comparably large replacement study has replaced it. But the picture has moved since 2020, and a few more recent data points are worth knowing if you’re managing denials in 2026:

• • • A January 2026 MGMA Stat poll of revenue cycle leaders found denials and appeals are now the single largest source of revenue cycle leakage, named first by 48% of leaders, ahead of front-end issues at 23%.
    • Premier Inc. estimated in February 2025 that claims adjudication now costs providers $25.7 billion industry-wide, with roughly $18 billion of that considered potentially unnecessary expense.
    • In Experian Health’s 2025 State of Claims survey of 250 revenue cycle leaders, providers themselves now point to missing or inaccurate claim data (50%), authorization issues (35%), and registration errors (32%) as their leading denial causes.
    • 288 new CPT codes and 614 new ICD-10-CM codes took effect across 2025, and practices still billing on outdated code sets are already seeing more coding-related denials in 2026 as a result.
    • MDaudit’s 2025 data shows dollars denied for medical necessity and documentation requests rose 70% from 2024 to 2025, the fastest-growing denial category by cost.
    • A 2026 analysis of 240 specialty practices found prior authorization denials now account for 34% of all first-pass denials, up from 22% in 2023.

In short, the underlying categories from 2020 still hold up directionally, but the mix is shifting toward claim-data completeness, authorization, and medical necessity documentation, exactly the areas payers have tightened scrutiny on most in the last two years.

Here’s how the original 2020 index breaks those categories down:

Registration and eligibility issues alone still account for over a quarter of denials in the original index, and within that category, coordination-of-benefits problems (a patient’s other insurance not being properly identified) make up the largest single share. That’s a front-desk fix, not a coding fix, and it’s exactly the kind of gap that’s cheap to close and expensive to ignore.

Here’s the part that should really get your attention: 95 to 100% of non-recoverable denials could likely have been avoided in the first place with the right prevention strategy in place. The cost of not acting isn’t just the denial itself. It’s the revenue that never comes back.

Category-level stats tell you where the problem lives. But when a denial actually lands on your remittance advice, it shows up as a specific code, not a percentage. Here are the 18 codes behind those categories, and exactly what to do about each one.

Every denial on your remittance advice falls into one of four buckets:

• • • CO (Contractual Obligation): an adjustment tied to your payer contract, often preventable, sometimes just standard math
    • PR (Patient Responsibility): money the patient owes, not a billing error
    • OA (Other Adjustment): usually a coordination-of-benefits issue
    • Remark Codes (CARC/RARC): extra detail explaining why a CO, PR, or OA adjustment happened

Knowing which bucket a denial lives in tells you immediately whether you’re looking at a fixable process gap, a patient collections issue, or a coordination problem, before you spend an hour investigating something the code already answered.

• • • What it means: The modifier attached to your CPT code doesn’t align with payer logic. Common culprits are modifiers 25, 59, LT/RT, or session-length modifiers like 90837 vs. 90834. This is a Medical Coding category denial.
    • Fix it: Build a modifier decision tree into your claim scrubber and audit modifier usage quarterly, especially for behavioral health session codes, where this one shows up constantly.

• • • What it means: Your ICD-10 code doesn’t medically justify the CPT code billed. This is a Medical Necessity category denial.
    • Fix it: Crosswalk every CPT to an approved ICD-10 list before submission. This is one of the most preventable, and most common, denials your practice will see.

• • • What it means: A required field is missing: NPI, date of service, place of service, authorization number. This is a Missing/Invalid Claim Data category denial, and per Experian Health’s 2025 survey, providers now rank this as the single leading cause of denials.
    • Fix it: Run every claim through a pre-submission scrubber with a 12-point completeness checklist before it leaves your system.

• • • What it means: The payer believes it already has a claim on file for the same date of service and procedure.
    • Fix it: Check claim status before resubmitting, and give it 7 to 10 business days rather than refiling out of frustration.

• • • What it means: A coordination-of-benefits issue, the single largest sub-reason inside the Registration/Eligibility category. The payer suspects the patient has other coverage that should pay first.
    • Fix it: Verify primary vs. secondary insurance at every single visit, not just at intake.

• • • What it means: The claim was submitted after the payer’s deadline, commonly 90 to 180 days for commercial payers, 12 months for Medicare.
    • Fix it: Build a filing deadline calendar by payer and flag any claim sitting unsubmitted for more than 14 days.

• • • What it means: A routine adjustment reflecting the gap between your billed charge and your contracted rate. Not technically an error.
    • Fix it: Not preventable, but worth tracking. Confirm your allowed amounts actually match your fee schedule expectations.

• • • What it means: The payer doesn’t consider the service medically necessary for the diagnosis submitted, or the diagnosis isn’t covered under that plan. This maps to both the Medical Necessity and Service Not Covered categories, and dollars denied here rose 70% from 2024 to 2025 per MDaudit.
    • Fix it: Confirm medical necessity policies (LCDs/NCDs for Medicare) before performing the service, especially for elective or borderline procedures.

• • • What it means: The payer considers this service bundled into a code already reimbursed, common with global surgical periods or same-day E/M plus procedure billing. This is an Overlapping Services denial, the top sub-reason in the Medical Coding category.
    • Fix it: Review NCCI edits before billing two codes on the same date, and apply the correct modifier (like -25 or -59) when the services are genuinely separate.

• • • What it means: The claim went to the wrong payer entirely, often after a plan change or a switch to Medicare Advantage. Another Registration/Eligibility category denial.
    • Fix it: Re-verify eligibility at every visit. Plan switches, especially during open enrollment, are the number one cause of this one.

• • • What it means: The patient has exhausted their visit or dollar cap for the service. Very common in physical therapy, and the second-largest sub-reason in Registration/Eligibility.
    • Fix it: Track visit counts against payer-specific caps in real time and flag patients approaching the limit before the visit, not after the denial.

• • • What it means: The payer’s utilization edits flagged the service as billed too often for the diagnosis. Common in recurring therapy or injection codes.
    • Fix it: Document medical necessity for frequency explicitly in the chart note, not just the claim.

• • • What it means: The service required prior authorization, and none is on file. This is the top sub-reason (Invalid Authorization) inside the Authorization/Pre-Certification category, and prior auth denials overall have grown to 34% of all first-pass denials in 2026, up from 22% in 2023.
    • Fix it: Build authorization verification into scheduling, not billing. By the time the claim is coded, it’s already too late to fix.

• • • What it means: The patient hasn’t met their deductible. This portion is legitimately their responsibility.
    • Fix it: Collect estimated deductible amounts at time of service using real-time eligibility checks rather than waiting for the EOB.

• • • What it means: Standard patient cost-sharing per their plan design.
    • Fix it: Post to the patient balance immediately after the EOB arrives and send statements within 48 hours. The longer the gap, the lower your collection rate.

• • • What it means: The specific service isn’t covered under the patient’s plan at all. This is a Service Not Covered category denial.
    • Fix it: Verify coverage for the specific CPT code, not just whether the patient is insured, before the appointment, especially for behavioral health carve-outs.

• • • What it means: A secondary payer adjusted its payment based on what the primary insurer already paid.
    • Fix it: Always attach the primary EOB when billing the secondary payer, and confirm the COB order is correct in the patient’s file.

• • • What it means: These CARC/RARC remark codes typically ride alongside a CO or PR denial to spell out exactly what’s missing: patient demographic gaps, plan document references, or extra documentation.
    • Fix it: Treat remark codes as your appeal instructions. They usually tell you precisely what the payer needs to reprocess the claim.

• • • Mental Health: CO-4 (session-length modifier errors like 90837 vs. 90834), CO-197 (ongoing authorization lapses), PR-96 (behavioral health carve-out exclusions).
    • Physical Therapy: CO-119 (benefit maximums), KX modifier denials (undocumented medical necessity), CO-4 (PT assistant modifier misuse). 
    • Dental/Oral Surgery: CO-4 (medical vs. dental code confusion when billing medical insurance), CO-11 (diagnosis not supporting medical necessity for oral surgery).

Here’s the uncomfortable math. Appealing a denial recovers revenue you’ve already earned, but it costs staff hours, delays cash flow by 30 to 60 days, and a large share of denied claims are simply never resubmitted at all, according to industry data compiled by Aptarro. That’s money your practice earned and will never see again.

The more profitable move is upstream: real-time eligibility verification, claim scrubbing against payer-specific edits, and authorization checks built into scheduling rather than billing. Practices that do this consistently land in MGMA’s top quartile, under 4 to 5% denials, instead of the 8 to 11% median most practices live with.

That gap, at scale, is real money. On a practice submitting 1,500 claims a month, the difference between an 11% and a 4% denial rate is roughly 100 fewer claims to rework every single month. That’s staff time, sanity, and revenue you get back.