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Type a claim adjustment reason code, or just what the payer told you, and get the official description plus the first thing to check. 77 codes covered. It runs entirely in your browser — nothing you type leaves your machine.
77 codes. Nothing is sent anywhere — this runs entirely in your browser.
The payer required prior authorization for this service and cannot find one attached to the claim.
Pull the authorization record and compare four things against the claim: the CPT code, the units, the date range and the rendering provider
Something on the claim is missing or malformed. On its own the code tells you nothing — the detail is in the remark code that comes with it.
Read the RARC remark code attached to the denial — CO-16 alone is not actionable and the remark is where the actual reason lives
The claim arrived after the payer’s filing deadline. This one is usually terminal, which is why it deserves attention before it happens rather than after.
Check whether you can prove timely submission: a clearinghouse acceptance report with a date inside the window will overturn many of these
The payer does not accept that the documentation supports the service. This is a clinical argument, not a clerical one.
Find the payer’s own coverage policy, the LCD or NCD for Medicare, and read what it actually requires — appeals that do not quote the policy mostly fail
A contractual write-off rather than a denial. It only becomes a problem when the allowed amount is wrong.
Compare the allowed amount against your contracted rate for that CPT. If they agree, post the adjustment and move on
The payer is bundling this code into another one on the same claim. Sometimes that is correct and sometimes it is not.
Check the NCCI edit pair and whether a modifier is permitted to break it — some pairs allow it and some do not, and billing a modifier on a pair that does not allow one is a compliance problem, not a shortcut
The payer already has this claim. Usually harmless, occasionally a sign that the original is stuck.
Find the original claim and check its status before doing anything else — most CO-18 work is wasted because the original was fine
The payer thinks somebody else is primary. Until coordination of benefits is corrected on their file, nothing on this claim will pay.
Call the patient before you call the payer. They can usually resolve the COB record themselves in one phone call, and the payer will not update it on your say-so
The patient was not covered on the date of service.
Re-run eligibility for the exact date of service and keep the transaction record
The payer accepts the service but not the quantity or the frequency at which it was billed.
Check the payer policy for the frequency limit and the period it runs over — a rolling twelve months and a calendar year are different things and practices lose money on that distinction
It went to the wrong place.
Re-verify eligibility and read which plan is actually active, including the plan type, not just whether coverage exists
A credentialing or enrollment problem rather than a claim problem: nothing this provider bills to this payer will pay until it is fixed, and it is rarely one claim.
Establish the effective date of the enrollment before touching the claims — that date tells you which claims are recoverable
The code and the modifier disagree, or a modifier the payer required was not there.
Read the RARC alongside it — CO-4 rarely tells you which modifier without one
The payer does not accept that the diagnosis submitted justifies the procedure performed.
Check the diagnosis pointers first. On a claim with four diagnoses, the wrong pointer is a frequent cause and it is a clerical fix
The plan does not cover this service at all. Distinct from medical necessity, which is an argument about evidence.
Read the RARC. CO-96 alone does not distinguish an exclusion from a coding problem, and those have opposite remedies
The patient has used up what the plan allows for this benefit in this period.
Confirm the remaining benefit directly with the payer and record the number and the date checked
The member ID and the name on the claim disagree with the payer’s record.
Re-run eligibility and copy the name and ID exactly as the payer returns them, not as the patient wrote them on the form
The service may be covered, but not when delivered or billed by a provider of this type.
Confirm the taxonomy code on the claim matches the provider’s actual enrollment, not merely their credential
The payer treats this service as part of another one, similar to CO-97 but usually driven by the fee schedule rather than an NCCI edit.
Check the status indicator on the fee schedule before appealing — some codes are never separately payable and an appeal simply wastes labour
The payer will not decide until it sees paperwork. Nothing happens until it arrives.
Read the RARC for exactly what is wanted — sending everything is slower than sending the right thing and often triggers a fresh review
An authorization exists. The problem is that you went past what it allowed — more units, more visits, or a longer date range than was approved.
Pull the authorization and count exactly what was approved against exactly what was billed — units, visits and date range, separately
The plan required a referral from the patient’s primary care physician and there is not one on file for this visit.
Check eligibility again and confirm whether the plan is referral-required — the answer differs by product line within the same payer
The service itself is excluded from this particular plan. This is a benefit design decision, not a coding error.
Read the benefit exclusion in the plan document rather than the payer’s general policy — this is a plan-level determination
This is a coordination of benefits adjustment on a secondary claim. It reflects what the primary payer already did rather than a problem with your claim.
Confirm this is genuinely a secondary claim and that the payer order is correct before doing anything else
The payer does not accept this provider as eligible for this service — an enrollment, credentialing or scope-of-practice problem rather than a coding one.
Check the provider’s enrollment status with that specific payer and product, not just their license
The payer does not expect a provider of this specialty to bill this code, based on the taxonomy attached to the claim.
Compare the taxonomy on the claim against NPPES and against the payer’s enrollment record — all three have to agree
Two things billed on the same day conflict under NCCI edits or a state fee schedule. The pair is the problem, not either code alone.
Look up the specific pair in the NCCI edit tables and read the modifier indicator: 0 means no modifier will ever override it, 1 means a modifier may be allowed with documentation
The two procedures billed cannot clinically or by rule both have happened at the same encounter.
Read the operative or encounter note and decide which code actually describes what was done
This service only pays when it is linked to another one, and the link is missing from the claim.
Identify what the qualifying service is — the code descriptor for an add-on code names its primary explicitly
The payer cannot match the patient to a member record. Usually a demographic or identifier mismatch rather than a coverage lapse.
Re-run eligibility with the details exactly as they appear on the card, then compare against what was billed
The appeal arrived after the payer’s deadline. The clock for appealing is separate from, and usually shorter than, the clock for filing.
Check the plan’s actual appeal window and what date it runs from before conceding — they differ by payer and by product
The payer applied this amount to the patient’s deductible. It is not a denial — it is the plan working as designed, and the balance is the patient’s.
Do not appeal this. Confirm the amount is right against the plan’s deductible and what has already been applied
The code you billed is not one the payer accepts for the setting the service happened in.
Check the encounter for where the service actually happened, not where the provider usually works.
The diagnosis code you sent is one the payer only accepts for a different age group.
Check the date of birth on the claim against the payer’s record and the chart. A registration typo is, in our experience, the most common cause.
The diagnosis code is one the payer only accepts for a different gender marker than the one on the claim.
Compare the gender marker on the claim with the payer’s record at eligibility — the mismatch is usually between systems rather than in the coding.
There is an authorization requirement here, and the number you sent is absent, wrong, or does not cover what was billed.
Pull the authorization and compare four things against the claim: code, provider, date range and units. One of them will not match.
The payer says this service is included in a capitated arrangement, so there is no separate fee-for-service payment.
Check eligibility for the date of service and identify which entity carries the risk.
The payer does not recognize this patient as a covered dependent on the subscriber’s policy.
Run eligibility for the date of service and confirm what the payer holds — not what the family described.
The subscriber’s policy covers the subscriber only, so a dependent’s claim has nothing to pay against.
Confirm the policy type at eligibility — employee-only is stated there and is not visible on a card.
The policy has a lifetime cap on this benefit and the patient has used it.
Confirm the maximum and the amount used with the payer, and get it in writing where the benefit is expensive.
The authorization was asked for and refused, and the service was delivered anyway.
Find the authorization denial and read why it was refused — the reason decides whether an appeal has anything to work with.
This is a secondary claim, and the secondary payer says the primary’s rules were not followed before it reached them.
Confirm the order of benefits with both payers before doing anything else.
The payer accepts the visit happened but not at the level you billed — usually an E/M downcode.
Read the note against the level billed before appealing — if the documentation does not support it, an appeal will not create support.
The payer does not cover the condition you billed, whatever the procedure was.
Read the payer’s coverage policy for the procedure and find the diagnosis list it accepts.
There is coverage, but the patient has not satisfied a condition the plan attaches to it.
Ring the payer and get the specific requirement that was not met and the date it will be, if it will be.
The code existed at some point but was not valid on the day the service happened.
Look the code up against the code set in force on the date of service, not today’s.
The modifier attached to the code was not valid on the day of the service.
Check the modifier against the rules in force on the date of service and against that payer’s own guidance.
Somebody is named as the referring provider who the payer will not accept in that role.
Verify the referring provider’s NPI against the national registry and the payer’s enrollment file.
The provider named as ordering the service is not accepted by the payer in that role.
Check the ordering provider’s enrollment status with that payer directly, and their revalidation date where it is a Medicare-family denial.
The payer asked you for something, and either nothing arrived or what arrived did not answer the question.
Find the original request and read exactly what was asked — most failed responses answered a different question.
The payer asked the patient for something — very often about other insurance or an accident — and did not get it.
Ring the payer and find out exactly what was asked of the patient and how they can supply it.
The plan pays only for its own network, and this provider was not in it for this service.
Confirm participation for the specific plan and product, not just the payer name. In our experience this distinction accounts for most of these denials.
Something was sent, and it did not contain what the payer needed.
Ask the payer specifically what was deficient. "Incomplete" is not actionable; the missing element is.
A statutory percentage reduction applied to a federal payment. It is not a denial and there is nothing to appeal.
Post it as an adjustment. There is no appeal and no correction — it is a statutory reduction, not a determination about your claim.
The managed care contract in force does not provide for payment of this service.
Read the contract’s covered services and carve-outs before appealing. Most of these are correct denials sent to the wrong entity.
The service is covered in principle but this instance did not meet the programme’s conditions.
Get the specific guideline that was not met from the payer, in writing where the amount justifies it.
The payer paid part of this procedure on another line or claim and has reduced this one to the difference, so the practice is not paid twice for the same work.
Find the earlier payment: pull every line paid for this patient on this date and identify the component the payer says it already covered.
The service is covered, but this instance went past a programme limit: more visits, units or sessions than the guideline allows.
Ask the payer which guideline and which limit — the number, the period, and how many units they count as used — in writing where the amount justifies it.
The payer is pointing you at the plan document: there is a restriction on this service and the document says what it is.
Read the CARC on the same line first. The remark explains; the reason code is what actually happened.
The payer cannot match the patient from what was sent.
Run eligibility and take the identifier exactly as the payer returns it, including any prefix or suffix.
The claim was rejected as unprocessable rather than denied. There is nothing to appeal — it has to be corrected and sent again as a new claim.
Do not file an appeal. There are no appeal rights on an unprocessable claim and the time spent is lost.
The payer needs clinical documentation it does not have.
Establish exactly what document is wanted, for which date of service, and in which channel.
The patient does not qualify for this particular service under their plan, even though they may hold coverage.
Read the CARC on the same line — the remark explains, the reason code determines the outcome.
The service was billed on the wrong form or in the wrong format for the payer.
Confirm which form and which bill type that payer requires for this service.
There is an authorization, and what was billed does not match what it covers.
Put the authorization and the claim side by side and compare code, provider, facility, dates and units. One will differ.
A published coverage policy for your region decided this, and that policy states exactly what would have been covered.
Find and read the actual policy. It lists the covered diagnoses and the documentation required, which makes this one of the most answerable denials there is.
The code billed only exists alongside a primary procedure, and no acceptable primary was on the claim.
Check whether the primary procedure was billed at all, and on which claim.
The line carries more units than the payer allows for that code on one date, so it rejected the quantity rather than the service.
Read the code’s unit definition and recount. Most of these are a units error, and a corrected claim with the right quantity pays.
An alert, not a denial: the payer processed the line under your contract and is pointing you at it. The reason code beside it carries the money.
Compare the allowed amount with the contracted rate for this code, this provider, this date. At or above the contract, post the adjustment and move on.
The secondary payer already has this claim — Medicare forwarded it automatically — and the copy you sent is the duplicate.
Do nothing to this claim. Find the crossover copy — the Medicare remittance carries MA18 when it forwarded the claim — and post from the secondary’s remittance when that copy adjudicates.
A facility claim problem: the three-digit type of bill in field 4 of the UB-04 does not fit the facility, the claim, or the frequency.
Read the payer’s billing guide for the facility type and set field 4 to the type of bill it names, with the right frequency digit.
An out-of-network service the payer processed under federal or state surprise-billing rules: the patient owes only the PR amount, and any dispute over the payment is with the payer, not the patient.
Post the patient responsibility exactly as shown and refund anything collected above it. Balance billing here is prohibited, and the remittance says so in the code.
A DMEPOS competitive bidding denial: for this item, in this area, Medicare pays only suppliers holding a contract, and this claim came from one that does not.
Check the current status of the Competitive Bidding Program for the product category and the patient’s ZIP code on the CMS DMEPOS competitive bidding site before anything else — rounds start and end, and the answer changes with them.
Medicare cannot match the beneficiary: the Medicare Beneficiary Identifier or the name on the claim does not agree with the entitlement record.
Run a Medicare eligibility check and take the MBI and name exactly as returned; the MAC portals also offer an MBI lookup.
The code on the line is not one the payer recognises for that date: deleted, mistyped, or from the wrong code set.
Validate the code against the code set in force on the date of service, then resubmit as a corrected claim with the right one.
The secondary payer will not adjudicate without the primary payer’s decision: what was allowed, paid and adjusted, line by line.
Send the secondary claim with the primary’s adjudication carried in the claim itself: allowed, paid and adjustment amounts with their group and reason codes, per line.
The NPI of the clinician who performed the service is missing from the claim, is not a valid NPI, or is not one the payer has linked to your group.
Check the NPI against the NPPES registry and put the individual’s NPI in the rendering provider field, with the group NPI as billing provider.
A denial is a group code, a reason code and usually a remark code. Read together they say who is liable, what is missing and what to do — CO-16 with M51 is a different afternoon from CO-16 with MA130. Every X12 reason and remark code, official text. More on remark codes →
Group code, reason code and remark code together. 408 reason codes and 1,216 remark codes, official X12 text. Runs in your browser: the tables load once as a file; what you type is not sent anywhere.
Yes, and there is nothing to sign up for. It runs entirely in your browser — nothing you type is sent anywhere, which matters when the thing you are looking up relates to a real claim.
The official text is the X12 claim adjustment reason code set, used by every United States payer. Everything after that description is our own working guidance, and it is labelled as such.
Link to it freely. If a code your team keeps hitting is missing, say so and it will be added — the guides are written from the codes people actually get stuck on rather than from a list.
Because somebody looking up a denial code at four in the afternoon is exactly the person who later needs somebody to work the queue. Being useful first is cheaper than advertising and it lasts longer.
Sources checked 2026-09-10.
The tool answers one question. A seat answers the queue.
Next step
These guides tell you what to do. A seat is somebody doing it, every working day, during your business hours.
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