The Physician Guide to Understanding Your Explanation of Benefits: Reading EOBs Like a Billing Expert

The Document That Controls Your Cash Flow

The Explanation of Benefits is the document that insurance companies send after processing a claim. It tells you what was billed, what the insurance company is paying, what adjustments are being applied, and what — if anything — the patient owes. It is, in essence, the final word on whether you are being paid correctly for the care you delivered.

Most physicians never look at their EOBs closely. That is understandable — EOBs are dense, technical documents filled with codes and categories that are not intuitive. But this lack of scrutiny is costing practices real money. Payment errors, systematic underpayments, and incorrect adjustments hide in EOBs all the time, and they are only caught by practices that know what to look for.

The Basic Structure of an EOB

Every EOB, regardless of payer, contains the same basic information: claim information identifying the patient, provider, and dates of service; billed charges showing what you submitted; allowed amounts showing what the payer considers the correct charge for the service; patient responsibility showing deductible, copay, and coinsurance amounts; plan payment showing what the insurance company is actually paying; and adjustment codes explaining any difference between billed charges and payment.

The most important comparison to make on every EOB is between the allowed amount and your contracted rate. If you are a participating provider with a negotiated fee schedule, the allowed amount should equal your contracted rate for that specific service. If it is lower, you have an underpayment that you are entitled to appeal.

Common EOB Adjustment Codes and What They Mean

EOBs use standardized codes to explain payment adjustments. The Claim Adjustment Reason Code (CARC) explains why a claim or service line was paid differently than billed. Understanding the most common ones helps you identify whether an adjustment is legitimate or an error.

CO-45 means the charge exceeded your contracted rate — this is the standard contractual adjustment and is legitimate. CO-97 means the service is included in another service billed — this may or may not be correct depending on the specific codes. CO-4 means the service was billed with an inconsistent modifier — this usually means you need to review your modifier usage. PR-1, PR-2, and PR-3 mean patient responsibility for deductible, coinsurance, and copay respectively.

The adjustment codes that should trigger immediate review are anything that results in a zero payment for a service you expected to be covered, any CO (Contractual Obligation) adjustment that seems larger than expected, and any OA (Other Adjustment) code that you do not recognize.

How to Identify Underpayments

Systematic underpayment identification requires comparing EOB payments against your fee schedule for every payer. This sounds straightforward but is genuinely complex in practice because you may have different contracted rates with hundreds of different payers, and rates may vary by service type, location, and contract tier.

The starting point is making sure your contracted fee schedules are loaded into your practice management system. With fee schedule data loaded, your billing system can automatically flag any payment that falls below the contracted rate. Without this data, catching underpayments requires manual review — which is why so many underpayments go uncaught.

The most common underpayment scenarios include payers applying the wrong fee schedule (your contract was updated but they are paying at old rates), payers misclassifying your specialty or provider type (which affects which fee schedule applies), and payers bundling services incorrectly (paying for one service when two separately billable services were delivered).

Medicare EOBs: Special Considerations

Medicare EOBs — called Medicare Summary Notices for beneficiaries and Remittance Advice for providers — have some unique features worth understanding. The most important is the distinction between assigned and non-assigned claims, which affects how payment flows and what you can bill the patient.

For participating Medicare providers, payment goes directly to the provider at the Medicare fee schedule rate, and the patient owes their standard cost-sharing. The key check on Medicare remittances is verifying that the payment matches the current year fee schedule for each code in your geographic area — Medicare fee schedules are updated annually and vary by location, so what Medicare paid last year for a given code may be different this year.

Building a Payment Variance Review Process

The most effective approach to catching EOB errors is systematic rather than ad hoc. Implement a process where a percentage of EOBs — ideally 100% for large-dollar claims, and a random sample for routine claims — are reviewed against contracted rates. Flag any variance above 5% for manual review. Track and trend payment variances by payer to identify systematic underpayment patterns that may indicate a contract interpretation issue.

When you identify a pattern of underpayment — the same payer paying below contracted rates for the same codes across multiple dates of service — escalate immediately. This is not a one-off error to appeal individually; it is a systemic issue that should be addressed at the contract level, typically through a direct conversation with the payer's provider relations team or, if necessary, formal dispute resolution under your contract.