A payment lands in the bank and the remittance lands in a folder, and someone reconciles the two by eye. That is where posting errors begin. An 835 carries the adjustment detail a paper explanation of benefits never shows, and most of the money a practice loses to posting sits in the adjustment fields rather than in the payment field. This is how to read an 835, which reason codes end in a write-off and which end in an appeal, and how unapplied cash accumulates when posting falls behind the deposit.
What this covers
- The 835 is the ASC X12 version 5010 electronic remittance advice. Medicare stops sending paper remittances to professional providers after 45 days.
- The group code assigns the unpaid balance: CO to the practice, PR to the patient. A beneficiary may be billed only on a PR adjustment.
- CARC 45 is a contractual write-off. Codes 16, 29, 97 and 197 are work: correct, resubmit or appeal.
- Remark code MA130 means the claim is unprocessable and carries no appeal rights. The only route back is a corrected claim.
- Unapplied cash is a payment recorded and attached to no claim. It hides the receivable it should have closed.
The payment field tells you what arrived. The adjustment fields tell you what you lost and whether you can get it back.Posting is a decision about every CAS segment.
The two documents answer the same question at different resolutions. A paper explanation of benefits states what the payer did to a claim. An 835 states it in coded segments a system can post without a keyer, at the claim level and at the service line, with a code for every adjustment. A practice posting from paper and a practice posting from the 835 are not doing the same job at different speeds. They are making different decisions.
What the 835 carries
The 835 is the ASC X12 version 5010 Health Care Claim Payment/Advice transaction, the electronic remittance advice standard HHS adopted under HIPAA. Medicare contractors send it as the electronic companion to a payment, and CMS states that all Medicare ERAs are in that format. X12 publishes the implementation guide as 005010X221A1.
The file is built from loops: 1000A for the payer, 1000B for the payee, 2000 for the payment, 2100 for each claim, 2110 for each service line. The segments inside those loops decide what gets posted. Posting from the wrong loop is how a line level unit error ends up as a claim level note that nobody can act on.
| Segment | What it holds | What you do with it |
|---|---|---|
| BPR | Payment amount, method, date | Tie it to the deposit |
| TRN | Trace number for the payment | Match the ACH addenda record |
| CLP | Claim status, billed, paid, patient responsibility | Post the claim outcome |
| CAS | Group code, reason code, amount, units | Decide write-off, rework or appeal |
| SVC | Line charge, allowed, paid, units | Post the line and check units |
| PLB | Provider level adjustments | Route to review, never auto-post |
Medicare’s remittance advice booklet describes three levels of balancing: transaction, claim and service line. At the line, the charge less the adjustments equals the line payment. At the claim, billed equals paid plus patient responsibility plus the CAS amounts. At the transaction level, BPR02 equals claim payments less the net PLB.
Read the adjustment segment first
The CAS segment holds the decisions. Each CAS carries one group code and one or more reason code triples, and CAS segments appear at the claim level in loop 2100 and at the line level in loop 2110. Medicare’s booklet notes the same adjustment will not appear at both levels on one remittance, so post from the most granular level the file gives you.
Claim level and line level adjustments answer different questions. A claim level CAS reduces the whole claim, which is what a payer does when eligibility or an authorization fails. A line level CAS inside loop 2110 reduces one service, which is what a payer does when a unit count, a modifier or a diagnosis pointer is wrong. Post a line level adjustment as a claim level one and the broken line stays invisible.
Confirm BPR02 equals the deposit and that TRN matches the ACH addenda record.
CLP03 is billed, CLP04 is paid, CLP05 is patient responsibility.
CO to a contractual write-off, PR to the patient balance, OA to review.
Posted payments equal the day’s deposits. Anything left over is unapplied cash with a name.
Group codes decide who owes
The group code assigns financial responsibility for the unpaid balance. CMS states the rule plainly: CO, contractual obligation, assigns responsibility to the provider, and PR, patient responsibility, assigns responsibility to the patient. X12 also publishes OA for other adjustments, PI for payer initiated reductions, and CR for a correction or reversal. PR is the only group code that creates a billable patient balance on a Medicare claim.
| Group code | Meaning | Posting action |
|---|---|---|
| CO | Provider liability | Write off against the contract. Do not bill the patient. |
| PR | Patient responsibility | Move to the patient balance and bill under practice policy |
| OA | Other adjustment | Review. Neither party is held responsible. |
| PI | Payer initiated reduction | Compare against the contract, then appeal or correct |
| CR | Correction or reversal | Reverse the original posting, then repost |
PI deserves its own queue. A payer initiated reduction is money the payer took back, and Medicare reports many of those at the provider level instead of against a claim: a deduction for a prior overpayment, a forward balance, or interest on a late payment. None of those has a claim to attach to, so they belong in a review queue.
A patient balance built from a CO adjustment is a compliance problem. Noridian’s group code guidance lists the charges a beneficiary may not be billed for, including late filing penalties, excess charges on an assigned claim and medical necessity denials. The same page warns suppliers may face penalties for billing outside PR.
Which reason codes are write-offs
The reason code names the cause. Group code plus reason code sets the action. X12 dates every code and marks replaced ones as deactivated, so an old code on a printed cheat sheet is a warning sign rather than a payer error. Every code below is current on the X12 list.
| Code | What it means | Posting action |
|---|---|---|
| CO-45 | Charge exceeds the fee schedule or contracted rate | Contractual write-off. Check the allowed amount against the contract. |
| CO-16 | Claim or service lacks information | Rework. Fix the field the remark code names and resubmit. |
| CO-29 | The time limit for filing has expired | Check the date of service against the payer’s limit. Appeal only where an exception applies. |
| CO-97 | Benefit included in another service already adjudicated | Review the bundling edit. Appeal or correct with a modifier when the services were distinct. |
| CO-197 | Authorization or notification absent | Compare the authorization on file with the dates of service, then appeal. |
| CO-50 | Not deemed medically necessary | Appeal with documentation that maps to the coverage policy. |
| PR-1, PR-2, PR-3 | Deductible, coinsurance, copayment | Move to patient responsibility and bill under practice policy. |
A write-off is final and an appeal is not. Sort the CO group by reason code before any dollar reaches the write-off column. CO-29 and CO-197 arrive in the same group as CO-45 and are often recoverable. What is left belongs in denial management, where the reason code sets the queue and the dollars set the order.
Remark code MA130 reads: Your claim contains incomplete and/or invalid information, and no appeal rights are afforded because the claim is unprocessable. Please submit a new claim with the complete/correct information. An appeal against an unprocessable claim is returned unaccepted, and the filing clock keeps running.
Remark codes carry the detail
A CARC gives the overall explanation and a RARC adds the specific one. X12 maintains both sets, and its CARC and RARC committees review change requests three times a year, according to the CMS page on EFT and remittance advice operating rules. A reason code of 16 without its remark code tells a biller nothing about which field to fix.
- N362: the number of days or units exceeds the payer’s maximum. On 97153 that is a units field, and the answer is a review of the authorization.
- M76: missing or invalid diagnosis. Check the pointer on the line as well as the claim.
- N522: duplicate of a claim processed, or to be processed, as a crossover. Check the Medicare crossover before rebilling.
- N479: missing explanation of benefits for coordination of benefits. Get the primary payer’s remittance first.
Remark codes ride in their own segments. The CMS 835 companion guide lists loop 2110 with an LQ health care remark code segment repeating up to 99 times, which is how a payer attaches several remarks to one line. Read the LQ segments before deciding a line is unappealable, because the remark often names the missing document.
CARC 16 requires at least one remark code, and X12’s usage note rules out an alert code for that purpose. Log the group code, the reason code and every remark code on the account.
Unapplied cash and posting lag
Money and information travel on separate tracks. The ACH deposit arrives on the payer’s schedule, and the 835 arrives when the payer or the clearinghouse releases it. The reassociation trace number ties them together: CMS requires health plans to place the X12 835 TRN segment in field 3 of the CCD+ addenda record, so a payment can be matched to its remittance without a human reading a bank statement.
When that match fails, the money sits in suspense as unapplied cash. Three states get confused. An unposted deposit is money in the bank with no remittance recorded against it. Unapplied cash is a payment recorded and attached to no claim. A credit balance is money applied in excess of what was owed, and it is the only one that ends in a refund.
Medicare stops sending paper remittances once ERA delivery is running, at 45 days for professional providers and 31 days for institutional providers. A practice posting from paper is posting from a document the contractor stops producing.
Under 42 CFR 401.305 a Medicare overpayment must be reported and returned within 60 days of the date it was identified, and the lookback runs six years. Money that stays unidentified in suspense does not become revenue, and a write-off is not a way to clear the account.
- Every deposit is matched to an 835 by trace number the day it lands.
- Every CAS carries a decision: write-off, patient balance, rework or appeal.
- Unapplied cash is aged and worked oldest first, with one owner.
- Nothing leaves suspense by write-off or by netting.
- The 60 day overpayment clock is logged from the identification date.
A team running outsourced medical billing services should be able to show you a daily reconciliation, an aging report for suspense, and a posting decision behind every adjustment group.
The clocks behind a posting decision
Posting decisions run against deadlines. A claim denied for a fixable reason is recoverable until the payer’s window closes. After that the same claim is a write-off, and follow-up does not change the outcome. The filing limit and the appeal window are separate clocks, so a claim can sit inside one while it is outside the other.
| Clock | Length | Runs from |
|---|---|---|
| Medicare timely filing | 1 calendar year | The date of service, per 42 CFR 424.44 |
| Medicare redetermination | 120 days | Receipt of the initial determination, presumed 5 days after the notice |
| MAC decision on a redetermination | 60 days | Receipt of the request |
| Medicare Advantage clean claims | 95 percent within 30 days | Receipt of the claim, per 42 CFR 422.520 |
| Medicare Advantage, non-contracted provider | 60 calendar days to pay or deny | The date of the request |
| Medicare overpayment return | 60 days | The date the overpayment was identified |
Calendar the appeal window from the remittance date, not from the day someone noticed the denial. Medicare presumes receipt five calendar days after the notice date, so a redetermination filed on day 118 of a 120 day window is already late. Interest on a clean claim Medicare paid late arrives in the PLB segment, one more reason provider level entries need their own queue.
A corrected claim is not an appeal, and the difference decides which clock applies. A CO-16 or a duplicate usually goes back as a corrected claim or a reopening, which fixes the record without arguing the payer’s decision. A CO-50 or a CO-197 goes back as an appeal, which argues it.
One habit holds the chain together. Post the remittance the day it lands, record the group code, the reason code and the remark code on the account, and let the code decide whether the dollar is written off, reworked or appealed.
835 posting questions
An explanation of benefits is a statement of what the payer did. An 835 carries the same information as an ASC X12 version 5010 transaction, with claim level and service line detail in coded segments a billing system can post without a keyer. Medicare stops sending a paper remittance to professional providers after 45 days of ERA delivery.
No. CMS states that group code CO assigns responsibility to the provider, and that a Medicare beneficiary may be billed only when an adjustment shows group code PR. The charges that arrive under CO include late filing penalties, excess charges on an assigned claim and medical necessity denials. Noridian warns that billing outside PR can carry penalties.
CARC 45 is the contractual write-off: the charge exceeds the fee schedule or contracted rate, and the difference is not collectible from the patient. Most other CO codes are work. Codes 16, 29, 97 and 197 point to a missing field, an expired filing limit, a bundling edit or an absent authorization, and each has a route back to payment.
Check the PLB segment first. BPR02 equals the claim level payments less the net of the provider level adjustments, so interest, recoupments and forward balances move the payment without touching a claim. Then check the trace number: TRN should match the addenda record on the ACH credit. A missing match leaves the deposit unposted.
You have 120 days from the date you receive the initial determination, and CMS presumes receipt five calendar days after the date on the notice unless there is evidence to the contrary. The Medicare Administrative Contractor then has 60 days to decide. Missing the window generally ends the appeal unless you show good cause.
Unapplied cash is a payment recorded and attached to no claim. It usually means a deposit and its remittance were never paired, or the claim control number on the remittance does not resolve to an open account. Clear it by finding what the payment covers and applying it there. A genuine excess becomes a credit balance.
The bottom line
The 835 and the paper explanation of benefits tell the same story, and only one of them can be posted without a keyer. Read the group code to see who owes the balance, read the reason code and the remark code to decide what happens next, and match the trace number on the day the deposit lands. A team that does those three things does not accumulate suspense.
How much of your last batch was never worked?
Send us one month of 835 files and your deposit log. We will reconcile every trace number, split the adjustments into write-offs, reworks and appeals, age the unapplied cash, and show you which reason codes cost the most. Our team runs medical billing services for medical practices, with a focus on ABA and behavioral health.
Request a free ERA posting auditThis article describes general billing practice and the payer and regulatory requirements in force at the time of writing. Contract terms, payer policies and state Medicaid rules vary, so confirm the filing limit, the group code definitions and the appeal address on your own remittance advice before you act.
