An Explanation of Benefits (EOB) is a statement your health insurance company sends after you receive medical care. It breaks down what your provider charged, what your insurance paid, and what you owe. It is not a bill. It’s a summary of how your claim was processed, and learning to read it takes just a few minutes once you know what each field means.
What Each Field on Your EOB Means
Most EOBs follow a similar layout regardless of your insurance company. At the top, you’ll see identifying information: your name, your insurance ID number, the claim number, and the date the EOB was generated. Below that, the claim details are typically organized into columns or labeled sections.
Date of Service: The date you actually received care. If you had multiple visits or procedures, each one gets its own line.
Provider Name: The doctor, lab, hospital, or other provider who treated you.
Provider Charges (Billed Amount): This is what your provider billed for the visit or procedure. It’s almost never what anyone actually pays. Think of it as the sticker price before any negotiated discounts.
Allowed Amount (Allowed Charges): This is the amount your insurance company has agreed to pay for that service based on their contract with the provider. The difference between the billed amount and the allowed amount is the “plan discount,” and if your provider is in-network, they’ve agreed to accept this lower rate. You don’t pay the difference.
Plan Paid: The portion your insurance company actually covered. This is the allowed amount minus whatever share falls to you through your deductible, copay, or coinsurance.
Member Responsibility (Your Cost): What you owe. This number is what matters most. It’s typically broken into subcategories: deductible (applied toward your annual threshold before insurance kicks in), copay (a flat fee per visit), and coinsurance (your percentage of the allowed amount after the deductible is met).
How the Math Works
The basic formula behind every EOB is straightforward. Your insurance starts with the provider’s billed charge, reduces it to the allowed amount, then subtracts whatever portion you’re responsible for based on your plan design. Here’s a simplified example:
- Provider charges: $500
- Allowed amount: $350 (the negotiated rate)
- Plan discount: $150 (nobody pays this)
- Applied to deductible: $200 (if you haven’t met your deductible yet)
- Plan paid: $120 (80% of the remaining $150)
- Your coinsurance: $30 (20% of the remaining $150)
- Your total responsibility: $230 (deductible + coinsurance)
If you’ve already met your deductible for the year, that $200 would shift to your insurance company, and your share drops dramatically. This is why checking your deductible status matters every time you review an EOB.
What Adjustment Codes Mean
Most EOBs include short codes next to line items that explain why a charge was adjusted, reduced, or denied. These are called Claim Adjustment Reason Codes, and while there are hundreds of them, a handful show up repeatedly.
Codes 1, 2, and 3 are the most routine. They simply label amounts applied to your deductible, coinsurance, and copay, respectively. Code 45 means the charge exceeded the maximum your plan allows for that service, so the insurer reduced it. Code 97 means the service was bundled into another procedure’s payment, which is normal for things like lab work done during a routine visit.
Other codes signal problems worth paying attention to. Code 50 means the insurer decided the service wasn’t medically necessary. Code 197 means prior authorization was missing. Code 29 means the claim was filed too late. Code 204 means the service isn’t covered under your current plan at all. If you see any of these and believe the service should have been covered, that’s your cue to look into filing an appeal.
You’ll also see group codes, usually two letters, that indicate who’s responsible for the adjustment. “CO” (contractual obligation) means it’s a discount your provider agreed to, and you don’t owe it. “PR” (patient responsibility) means that amount falls to you. If a large charge is coded “PR” unexpectedly, that’s worth investigating.
How to Spot Errors
EOBs contain mistakes more often than most people realize. The most common errors are simple but costly: a wrong date of service, a procedure listed that you didn’t receive, or duplicate charges for the same service. Start by comparing the date and provider name against your own records. If you kept any visit summaries, discharge papers, or appointment confirmations, check them against the EOB line by line.
Watch for services billed separately that should have been bundled together. Some providers bill each component of a visit as a standalone charge, which can inflate costs or trigger separate copays. Also look for charges from providers you don’t recognize. In hospital settings especially, you may see bills from radiologists, anesthesiologists, or pathologists you never met directly. These aren’t necessarily errors, but they’re worth verifying.
If the billed amount looks unreasonably high, compare the allowed amount. A large gap between the two is normal for in-network providers since the discount is built into the contract. But if you went out of network, you could be responsible for the full difference between billed and allowed amounts, sometimes called “balance billing.” Federal protections under the No Surprises Act limit this practice for emergency services and certain situations where you didn’t choose the out-of-network provider.
What to Do if a Claim Is Denied
A denial on your EOB doesn’t have to be the final word. You have up to 180 days after learning a claim was denied to file what’s called an internal appeal with your insurance company. The process typically starts with a letter that includes your name, claim number, and health insurance ID number, along with any supporting information that explains why the service should be covered.
If the denial was based on medical necessity (code 50, for example), ask your doctor to write a letter explaining why the treatment was needed. Send that letter along with your appeal. Insurers overturn denials more often than people expect, particularly when clinical documentation supports the claim.
If the internal appeal is denied, you can request an external review, where an independent third party evaluates the case. Your EOB or denial letter should include instructions for both processes, including where to send your appeal and any deadlines beyond the 180-day window for specific situations.
Comparing Your EOB to Your Medical Bill
Your EOB arrives before or around the same time as the actual bill from your provider. The “member responsibility” amount on the EOB should match what your provider bills you. If the provider’s bill is higher than what the EOB says you owe, don’t pay the difference without calling both the provider’s billing office and your insurance company first.
Keep your EOBs for at least a year, ideally until you’ve confirmed that all charges for a given plan year are resolved. If you access EOBs through your insurer’s online portal, you can typically search past claims by date, provider, or claim status. The digital versions contain the same information as paper EOBs, and most portals let you download or print copies for your records.