What are 5 reasons a claim might be denied for payment? Eligibility that did not match the date of service, missing or wrong information on the claim itself, a plan limitation or exclusion, a medical necessity or authorization failure, and a timing problem such as late filing, a duplicate, or the wrong payer billed first. Four of those five are created inside your office before the claim is ever transmitted. Only one of them is a genuine clinical disagreement with the payer.
That distinction is the whole game. A practice that treats all denials as arguments to win spends its week writing appeals for problems a two minute correction would have solved.
What are common reasons claims get denied?
Start with the remittance, not with the chart. Every adjustment on an electronic remittance carries a group code and a reason code, and that pair sorts the denial into one of the five categories faster than any conversation with the payer will.
| Category | Typical codes you will see | Who created it | Where it gets resolved |
|---|---|---|---|
| Eligibility or patient identity | CO-27, CO-31, CO-109 | Intake and verification | Corrected claim or refile to the right payer, rarely an appeal |
| Missing or wrong claim information | CO-16 with a remark code naming the field | Claim build | Corrected claim, inside the original filing window |
| Plan limitation or exclusion | CO-96, CO-119, CO-151 | Plan design, verified or not | Patient balance if disclosed in advance, appeal only if applied incorrectly |
| Medical necessity or authorization | CO-50, CO-197 | Clinical documentation | Appeal with radiographs, charting, and a narrative |
| Timing, duplicates, payer order | CO-18, CO-22, CO-29 | Workflow and follow up | Proof of timely filing, or refile in the correct order |
Before you work any of them, read the group code. CO means contractual obligation, and the amount is a write off you agreed to absorb when you signed the participating provider agreement. PR means patient responsibility, and the balance can move to the patient statement. Billing a patient for a CO amount is a contract violation in most participating agreements, which is the real answer behind the search people type as "health insurance claim denied but I owe nothing." The claim was denied, and the contract still says the patient owes nothing.
Reason 1: coverage did not match the date of service
The plan was active when you verified it in January and terminated in March. The patient switched employers and kept the old card. The subscriber ID had a prefix your software dropped. The patient is covered, but by a different administrator than the card suggests.
These arrive as CO-27 for expenses incurred after coverage terminated, CO-31 for a patient who cannot be identified as the payer's insured, or CO-109 when the claim went to a payer who does not hold the contract. None of them are appeals. They are refiles, and the only real cost is the time lost between the date of service and the day someone noticed.
The prevention is unglamorous: verify on the day of service, not the day of scheduling, and capture the payer's reference number and the date on the record. A benefits check from six weeks ago is a historical document.
Reason 2: the claim was missing something the payer needs
CO-16 is the workhorse denial, and on its own it tells you nothing. The remark code attached to it names the missing element. In dental claims the recurring offenders are tooth number, surface, quadrant, arch, a missing or mismatched provider identifier, a missing primary carrier remittance on a secondary claim, and an attachment that was referenced but never arrived.
The tooth level data matters more in dental than the diagnosis code does, which is the biggest structural difference from medical billing. A D2740 with no tooth number is unadjudicable. A D4341 with no quadrant is unadjudicable. A D2950 submitted without the crown it supports invites a bundling denial under CO-97.
These clear on a corrected claim, and they clear fast. The danger is not the denial, it is the 45 days it sits in a queue nobody is reading while the filing clock runs.
Reason 3: the plan simply does not cover it, or not yet
This is the category practices argue with when they should be quoting it. Frequency limits, waiting periods, annual maximums, age limits, missing tooth clauses, and flat exclusions are provisions the employer group bought. The payer is applying a contract, not making a judgment call.
Expect CO-119 when a benefit maximum for the period has been reached, CO-151 when the payer decides the frequency submitted exceeds what the plan allows, and CO-96 for a plain non covered charge. Common examples in a general practice:
| Service | CDT code | Limit commonly seen | What denies |
|---|---|---|---|
| Adult prophylaxis | D1110 | 2 per 12 months | The third cleaning in a rolling year |
| Bitewings, four images | D0274 | 1 per 12 months | A second set taken 10 months later |
| Complete series | D0210 | 1 per 36 to 60 months | A retake inside the interval |
| Fluoride varnish | D1206 | Age capped, often in the teens | An adult application |
| Periodontal maintenance | D4910 | Interval tied to D4341 history | Maintenance with no scaling history on file |
Every one of those limits varies by plan, because employer groups choose them. Never assume a carrier applies the same frequency rule across its book of business. Verify the limit per plan, and capture whether it runs on a calendar year or a rolling 12 months from the last service date, because that single detail decides whether the patient is eligible today or in March. Our list of the top 10 reasons for dental insurance claim denials covers the rest of the limitation family.
Reason 4: the payer is not persuaded the service was necessary
CO-50 says the payer does not deem the service a medical necessity. CO-197 says authorization or precertification was absent. They feel similar and they are worked differently.
CO-197 is usually procedural. The plan required a predetermination, nobody sent one, and the remedy is to find out whether retroactive review is permitted. Many plans allow it for urgent care and refuse it otherwise.
CO-50 is the only one of the five reasons that is a real clinical argument, and it is almost always a documentation failure rather than a treatment failure. The radiograph was taken and never attached. The perio chart exists in the software and was never exported. The narrative said "patient in pain" instead of naming the finding, the duration, and what conservative treatment was already tried. Surgical extractions under D7210, bone grafts, and implant cases draw this denial most often, and we have walked through both: why a dental implant claim gets denied and why a bone graft claim gets denied. For the appeal itself, start with next steps on a not medically necessary denial.
Reason 5: the timing or the order was wrong
Three separate failures live here.
Late filing produces CO-29, and the window is contractual rather than legal. It commonly runs from 90 days to 12 months from the date of service depending on the participating agreement, with 180 days a frequent midpoint. Read your own contract instead of assuming, and see what to do when a claim is denied for timely filing, because a proof of timely submission often wins the appeal outright.
Duplicates produce CO-18. They are usually self inflicted, created when someone resubmits a claim that was already pending rather than checking status.
Payer order produces CO-22, and the fix requires knowing which plan pays first. For a patient with two plans, the plan where they are the subscriber pays before the plan where they are a dependent. For a child covered by both parents, the birthday rule applies in most states: the parent whose birthday falls earlier in the calendar year, by month and day and not by year of birth, holds the primary plan. A court order in a divorce overrides the birthday rule. Coordination rules are set at the state level, so confirm yours with your state insurance department.
What are the three types of claim denials?
Practices lose time by treating these as one queue. They are three, with different owners and different clocks.
| Type | Where it stops | Counts as a claim | How to work it |
|---|---|---|---|
| Rejection | Clearinghouse or payer front end edit, before adjudication | No | Fix the data, resubmit as a new claim, no appeal rights |
| Soft denial | Adjudicated, payable once you send more | Yes | Send the attachment or narrative, resubmit as a corrected claim |
| Hard denial | Final determination | Yes | Appeal in writing inside the appeal window, or write off or bill the patient per the group code |
The rejection distinction is the one that costs money. A rejected claim never entered the payer's system, so the payer has no record of it, no appeal rights attach, and the timely filing clock has been running the entire time it sat in a rejection report nobody opened. Check the acknowledgment reports daily. A claim you believe is pending and the payer has never seen is the most expensive item in your accounts receivable.
The second useful split is administrative versus clinical. Administrative denials are the first, second, and fifth reasons above and they belong to the business team. Clinical denials are the fourth and they need the dentist's time. Routing every denial to the same person guarantees the clinical ones sit.
What are the top 5 denials in medical billing?
The medical side ranks them slightly differently, which is worth knowing when you cross bill a case to medical for sleep apnea, trauma, or surgical extractions.
| Rank | Medical billing | Dental equivalent |
|---|---|---|
| 1 | Missing or invalid information, CO-16 | Same, but tooth and surface data rather than diagnosis specificity |
| 2 | Prior authorization not obtained, CO-197 | Less common, predeterminations are usually optional |
| 3 | Coverage terminated or patient not identified, CO-27 and CO-31 | Identical, and just as preventable |
| 4 | Medical necessity not established, CO-50 | Concentrated in surgical, implant, and periodontal cases |
| 5 | Timely filing expired, CO-29 | Identical, with shorter windows on some dental contracts |
Two differences matter operationally. Medical claims require ICD-10-CM diagnosis coding and a place of service code, and a dental claim crossed to medical without them will reject before adjudication. Dental claims carry frequency and annual maximum limits that have no real medical analog, which is why plan limitation denials rank far higher in a dental practice than they do in a physician's office.
Initial denial rates across healthcare are commonly quoted in the 5 to 15 percent range, and the figure you should manage is your own, not the industry's. Divide denied claim lines by total claim lines submitted in the same month, then split that number by payer. One payer is almost always responsible for an outsized share, and it is rarely the one staff complain about.
Why could a claim be denied? A 15 minute triage
Work the claim on your desk in this order. It takes about 15 minutes and it prevents the most common waste, which is appealing something that needed a correction.
- Read the group code first. CO or PR decides whether the balance can move to the patient. Do not send a statement before you have checked this.
- Read the reason code, then the remark code. The reason code gives the category. The remark code usually names the exact field or document.
- Decide rejection or denial. If the payer has no claim on file, it was a rejection. Resubmit as a new claim, and do not waste a day writing an appeal for a claim that does not exist.
- Check the filing clock. Compare the date of service to the contractual filing limit. If the window is still open, a corrected claim is faster than an appeal every time.
- Check the appeal clock separately. The appeal window runs from the remittance date, not the date of service. As of this writing, ERISA governed group health plans generally must allow at least 180 days to file an internal appeal of an adverse benefit determination. Confirm the specific deadline in the plan document and with your state insurance department, since rules change.
- Pull the evidence before you write anything. Radiographs, perio charting, the verification reference number and date, the original submission acknowledgment.
- Record the reason code against the payer and the plan. One denial is an incident. Six of the same code from the same payer is a process defect you can fix once.
Five checks that stop most of these before the claim goes out
Prevention is boring and it is where the money is. None of these require new software to start.
- Verify on the day of service and store the reference number. Eligibility denials disappear almost entirely with this one habit.
- Run a pre transmission scrub for tooth, surface, quadrant, and provider identifier. These four fields cause the majority of CO-16 denials in dental claims.
- Attach at submission, not on request. If a procedure has ever needed a radiograph or narrative at that payer, send it the first time.
- Capture frequency history per patient, not per year. Rolling 12 month limits are the most misquoted provision in dentistry.
- Read acknowledgment reports daily. A rejection found on day 3 is free. The same rejection found on day 120 may be uncollectable.
Curo reads the full benefit detail during verification, prices the treatment from what the plan actually allows, and tracks every denial reason code back to the payer and plan that produced it, so repeat causes surface as patterns rather than as one off frustrations. If you want the mechanics of working the queue systematically, our guide to why dental claims get denied and how automation fixes it goes deeper, and our denial management overview shows how the reason code routing works.
What to do with the stack on your desk tomorrow
Do not work it oldest first. Sort it by reason code, then by payer, and work the largest group first. Denials cluster, and clusters have one cause. Twelve CO-16 denials from the same payer are usually one missing field in one template, and fixing the template clears all twelve plus the ones you have not received yet.
Then set a rule that no denial gets touched twice without changing something. If a claim comes back a second time with the same code, the correction was wrong, and resubmitting it a third time is not a plan. Pick up the phone, get the adjudication detail, and write down what the payer actually needs. That single note, filed against the payer and the plan, is worth more than the claim it came from.