How to Read an EOB Before You Post the Payment

Most therapy practices read an explanation of benefits the way most people read a receipt: glance at the total, file it, move on. That habit is affordable right up until it is not. A denial at least announces itself — it shows up on a report and demands a response. An underpayment does not. It arrives inside a remittance that says “paid,” gets posted in thirty seconds, and disappears into the ledger. The only moment anyone can catch it is the moment of posting, and only if the person posting knows what each field on the remittance is actually asserting.

An explanation of benefits (EOB) is the payer’s statement of how it adjudicated a claim: what was billed, what the plan allowed, what it subtracted and why, what the patient owes, and what it paid. The electronic version is the electronic remittance advice (ERA). Under HIPAA, payers send ERAs in a standard format — the X12 835 transaction — and they must explain every adjustment using standardized code sets rather than their own proprietary codes. That standardization is the reason this article can exist: the same reading skill works across payers, because the grammar of the document is regulated even though the amounts are contractual.

Two code sets do the explaining. Claim adjustment reason codes (CARCs) say why an amount was not paid, and remittance advice remark codes (RARCs) add supplementary detail. Both lists are maintained by the X12 standards body and updated three times a year, which is why a code you have never seen before is a lookup, not a mystery. Each CARC also arrives attached to a group code that assigns the liability for the unpaid amount — and that pairing, more than anything else on the page, is what payment posting has to get right.

Strip away the formatting differences between payers and every remittance line makes the same five assertions. The billed amount is what you submitted. The allowed amount is what the payer says the service is worth under this patient’s plan — for an in-network claim, this is the number your contract governs. The adjustments are the difference between billed and allowed, each one tagged with a group code and a reason code. The patient responsibility is the share of the allowed amount assigned to deductible, coinsurance, or copay. And the paid amount is what is left: allowed, minus patient responsibility, minus any other adjustments.

That arithmetic is the whole discipline of payment posting. Billed minus adjustments must equal allowed. Allowed minus patient responsibility must equal paid, absent another coded adjustment. When the numbers on a line do not close, the line is telling you something — a bundled service, a secondary-payer interaction, a fee-schedule change — and posting it anyway just moves the confusion into your ledger where it is far more expensive to find.

Every adjustment arrives as a pair: a group code that says who absorbs the amount, and a reason code that says why. Medicare limits its contractors to four group codes, and commercial payers use the same set, so this table covers nearly everything a therapy practice will see.

The reason codes riding on those groups are standardized too. A handful account for most therapy remittance lines: CARC 1, 2, and 3 are the patient-responsibility trio — deductible, coinsurance, and copayment. CARC 45 is the contractual write-down: “charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.” CARC 97 means the payer considers the service bundled into another line it already paid. And CARC 23 flags the impact of a prior payer’s adjudication on a secondary claim. Anything unfamiliar goes to the X12 code list, not to guesswork.

The example above is a reading skill. This is the workflow that applies it every time, so catching an underpayment does not depend on whoever happens to be posting that day. It assumes you post from the ERA rather than the paper EOB wherever possible — the electronic remittance carries the same adjudication in a machine-postable form, which is precisely what makes unreviewed auto-posting both efficient and dangerous.

1. 01

   Reconcile the deposit to the remittance before touching claims

   The remittance total and the bank deposit (or check) must match. If they do not, stop — you may be looking at the wrong remittance, a split payment, or a payer offset recouping money from an earlier claim.

2. 02

   Close the arithmetic on each line

   Billed minus adjustments equals allowed; allowed minus patient responsibility equals paid. A line that does not close gets investigated before it gets posted, not after.

3. 03

   Compare every allowed amount to the contracted rate

   This is the underpayment check, and it requires your fee schedules to be somewhere the poster can see them — in the billing system or a maintained rate table, not in a filing cabinet. A remittance can be internally perfect and still underpay the contract.

4. 04

   Honor the group codes when posting

   CO amounts become contractual write-offs; PR amounts become patient balances. Miscoding this either bills patients for money they do not owe or silently absorbs balances the plan assigned to them.

5. 05

   Route exceptions instead of resolving them at the keyboard

   Underpaid lines, bundling you disagree with, unfamiliar codes, and unresolved arithmetic go to a variance queue with the remittance attached. Posting should be fast because judgment calls happen elsewhere — the same separation that makes a denial workflow effective.

6. 06

   Log the pattern, not just the instance

   When a variance resolves, record the code, plan, and root cause. One mispriced code found in March and again in May is not two events; it is one systemic error with a date range — and a stronger appeal.

For Medicare Part B, the patient-responsibility math is published rather than contractual: after the annual deductible, the beneficiary owes 20% of the Medicare-approved amount for covered services, which is why PR-2 lines on Medicare remittances are so predictable. If a Medicare line’s units look wrong rather than its rate, the discrepancy is usually upstream in minute counting — the Medicare 8-minute rule governs how timed-code minutes become billable units. And when reading the remittance turns into disputing it, the claim-denial workflow covers classification, deadlines, and appeals; the billing features page shows how Callie handles claims and remittances.

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“A denial is the payer disagreeing with you out loud. An underpayment is the payer disagreeing with you quietly, and hoping you post it anyway.”