What is an ERA?
An Electronic Remittance Advice, the X12 835, is the payer's electronic explanation of a payment: every claim and service line it covers, what was paid, and why the rest wasn't.
ST*835*0001*005010X221A1~Start of an 835 remittance.BPR*I*111.22*C*ACH*CCP*…*20260320~The payment: $111.22 by ACH, effective March 20.TRN*1*1004821*1512345678~Trace number 1004821. The same number travels with the EFT deposit, which is how the two are matched.CLP*CLM00418*1*320*111.22*25.68*12*2026031488731~Claim CLM00418, processed as primary: billed $320.00, paid $111.22, patient responsibility $25.68.SVC*HC:99214*210*102.72~Office visit: billed $210.00, paid $102.72.CAS*CO*45*81.6~Contractual adjustment, CO-45: $81.60 written off.CAS*PR*2*25.68~Coinsurance, PR-2: $25.68 the patient owes.SVC*HC:36415*25*8.5~Blood draw: billed $25.00, paid $8.50.CAS*CO*45*16.5~Contractual adjustment of $16.50.SVC*HC:93000*85*0~ECG: billed $85.00, paid nothing.CAS*CO*50*85~Denied as not medically necessary, CO-50.The ERA is the electronic twin of the paper EOB. Because it’s structured data, a billing system can post it automatically, which is why most payers send ERAs and most providers enroll to receive them.
What’s inside an 835
- The payment (BPR and TRN): amount, method, date, and the trace number that links it to the EFT in the bank account.
- Each claim (CLP): your claim number, its status, billed, paid, patient responsibility and the payer’s claim number.
- Each service line (SVC): the procedure code, billed and paid amounts.
- Adjustments (CAS): a group code (CO, PR, OA or PI) with a reason code and amount for every dollar not paid.
- Remarks: RARCs that explain the adjustment in more detail.
- Provider-level adjustments (PLB): interest, recoupments and other money not tied to one claim.
Where auto-posting falls short
Auto-posting handles the clean lines. What’s left is the hard part: lines that don’t match a claim, reversals and corrections, recoupments taken from other patients’ payments, denials that need to start a workflow, and payments that arrive without their deposit, or deposits without their 835. Those are where posting teams spend their day.
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