6.2 EOB/ERA reading & payment posting

From Claim to Payment: Reading the EOB and ERA

Once a payer finishes adjudicating a claim, it returns a remittance document that explains the outcome. The two formats a CBCS sees every day are the Explanation of Benefits (EOB) and the Electronic Remittance Advice (ERA). The EOB is a human-readable statement — usually paper or PDF — sent to the patient and often the provider. The ERA is the electronic version, transmitted in the HIPAA-standard 835 transaction, that posts automatically into the practice-management system. An EOB is not a bill; it tells the patient what the plan paid and what, if anything, the patient still owes.

The Core Money Fields

Every remittance walks a single service line from the charged amount down to a final balance. Understanding these fields is the heart of payment posting:

The allowed amount is the pivot point. Because a participating (par) provider has a contract, the difference between the billed charge and the allowed amount becomes a contractual write-off that can never be billed to the patient — doing so is illegal balance billing. From the allowed amount the plan subtracts patient cost-sharing (deductible first, then coinsurance or copay) and pays the remainder. A quick worked example: billed $200, allowed $120, patient deductible $20 — the provider writes off $80, the patient owes $20, and the plan pays $100.

For a non-participating (non-par) provider who does not accept assignment, the rules differ: there is no full contractual write-off, and Medicare caps how much extra the patient can be charged through the limiting charge. Knowing whether the rendering provider is par or non-par tells the poster whether the billed-minus-allowed difference is a write-off or a legitimate patient balance. Every EOB/ERA also carries a header with the payer name, check or EFT number, payment date, and provider identifiers; the poster verifies these before touching any account so payments are never applied to the wrong practice or tax ID.

CARC and RARC Codes

Standardized codes explain every adjustment so the biller does not have to guess. A Claim Adjustment Reason Code (CARC) states why an amount was adjusted (for example, CARC 45 "charge exceeds fee schedule/allowed amount," or CARC 1 "deductible"). A Remittance Advice Remark Code (RARC) supplies a supplemental explanation or instruction (for example, "missing/incomplete documentation"). Each CARC is paired with a group code that assigns financial responsibility:

• CO — Contractual Obligation: the provider absorbs it (the write-off).
• PR — Patient Responsibility: deductible, coinsurance, copay, or non-covered charge billable to the patient.
• OA — Other Adjustment: used when neither CO nor PR fits.
• PI — Payer Initiated Reduction: a reduction the payer, not the contract, is responsible for.

Reading CARC + group code together tells the poster exactly where each dollar goes: CO 45 becomes a write-off, while PR 1 becomes patient balance.

Payment Posting Step by Step

Payment posting is the process of recording the remittance against each patient's account. Whether done manually from a paper EOB or automatically from an 835 ERA (often called auto-posting), the steps are the same:

1. Match the remittance to the correct patient, claim, and date of service.
2. Post the payment from the plan to the specific service line.
3. Post the contractual adjustment (the CO write-off) so the account reflects the agreed allowed amount.
4. Assign patient responsibility (PR amounts) so the patient can be billed the correct balance.
5. Route any remaining balance to a secondary payer via coordination of benefits (COB), or move it to patient statements if no other coverage exists.
6. Reconcile the total posted against the check or EFT and the 835 control totals so nothing is lost.

Accuracy here protects revenue: if the contractual write-off is not posted, the account overstates what the patient owes; if a payment is posted to the wrong line, aging reports become unreliable and follow-up stalls.

Denials, Zero-Pay Lines, and the Secondary Claim

Not every remittance line carries a payment. A line may show the full charge moved to CO, or a denial CARC with $0 paid. The poster flags these so the denial-management workflow can act. When a secondary insurer exists, the primary EOB/ERA is required documentation to bill the secondary plan — the secondary pays based on what the primary allowed and left as patient responsibility. Careful reading of the EOB/ERA therefore feeds three downstream tasks at once: patient billing, secondary claims, and denial appeals. Enrolling in electronic 835 remittance and EFT speeds this cycle because the ERA can auto-post to hundreds of accounts in minutes while preserving the CARC/RARC detail a biller needs to reconcile and work exceptions.