What is an EOB?
An Explanation of Benefits is the payer's statement of how it processed a claim: what was billed, what it allowed, what it paid, and what the patient owes.
Explanation of Benefits
- Payer
- Example Health Plan
- Patient
- Alex Sample
- Member ID
- XEH481207733
- Claim number
- 2026031488731
- Date of service
- 03/14/2026
- Payment
- EFT 1004821, $111.22
| Service | Billed | Allowed | Adjustment | Patient owes | Paid |
|---|---|---|---|---|---|
| 99214 Office visit | $210.00 | $128.40 | $81.60 CO-45 | $25.68 PR-2 | $102.72 |
| 36415 Blood draw | $25.00 | $8.50 | $16.50 CO-45 | $0.00 | $8.50 |
| 93000 ECG | $85.00 | $0.00 | $85.00 CO-50 | $0.00 | $0.00 |
| Claim total | $320.00 | $136.90 | $183.10 | $25.68 | $111.22 |
- Billed minus allowed is the contractual adjustment, group code CO with reason 45. The provider writes it off and can't bill the patient for it.
- PR-2 is coinsurance: 20% of the $128.40 allowed. The patient owes it.
- The ECG was denied with CO-50: not medically necessary in the payer's view. It needs an appeal with records, or a write-off.
- The EFT number ties this payment to the deposit in the bank account.
An EOB is how a payer explains its decision on a claim. Providers receive one for every claim the payer processes, usually several claims to a page, and patients receive their own version that clearly says it is not a bill.
EOB or ERA?
They carry the same information. The EOB is the paper or PDF version, written for people. The ERA is the electronic version, an X12 835 file that a billing system can post automatically. Most large payers send ERAs; many smaller payers, workers’ compensation carriers and auto insurers still send paper.
What’s on an EOB
- Claim and patient details: the payer’s claim number, the member ID and the dates of service.
- Every service line: what was billed, what the payer allowed under its contract, and what it paid.
- Adjustments: each one with a group code (CO, PR, OA or PI) and a claim adjustment reason code, often with a remark code that adds detail.
- Patient responsibility: deductible (PR-1), coinsurance (PR-2) and copay (PR-3).
- Payment details: the check or EFT number and the total paid, which must match the deposit.
Why paper EOBs cost so much
A person has to key every line into the billing system by hand. One EOB can hold dozens of patients, every payer lays its page out differently, and a typo posts money to the wrong claim or sends the wrong balance to a patient. Denials buried on page four are easy to miss until the appeal window has closed.
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