How to read an explanation of benefits, line by line

Most people meet an explanation of benefits, or EOB, the same way: an envelope or portal message arrives weeks after a visit, with a column of large numbers, a column of smaller ones, and a line that seems to say you owe something. Then a bill from the provider arrives, and its numbers do not quite match. The first document is the subject here. It shows what each part of an EOB means, works through an invented EOB line by line, reconciles it to an invented provider bill, and then covers what to do when the two disagree.

The structure follows the CMS consumer guide to explanations of benefits, part of its medical bill rights pages, and the HealthCare.gov glossary, both checked October 22, 2026. Insurers lay out their EOBs differently, and the labels on yours may vary, but the logic is the same on every one.

What is on an EOB, top to bottom

CMS lists the parts a typical EOB contains. Find each of them on yours before reading any dollar amount.

The payee row deserves a second look. If your plan sent its payment to you rather than to the provider, which can happen with an out-of-network provider, the money is meant to go to the provider, and the provider's bill may show the full charge. That is not an error; it is a payment you need to pass along.

The four money columns, in the order the plan used them

Every dollar figure on an EOB comes from one sequence. The plan starts with the provider's charge, cuts it to the allowed amount, applies your plan's cost sharing, and pays the rest.

1. Billed, or provider charges

What the provider asked for, at its full list rate. For an in-network provider, this number is mostly informational: you will not pay it.

2. Allowed, or allowed charges

HealthCare.gov defines the allowed amount as the maximum a plan will pay for a covered service, also called the eligible expense, payment allowance or negotiated rate. For in-network care it is the rate your plan agreed with the provider. Everything you owe for a covered service is figured from this number, not from the billed amount. The gap between billed and allowed is often labeled a discount, a provider adjustment, or "not your responsibility."

3. Paid by insurer

What the plan paid after applying your deductible, coinsurance and copay to the allowed amount. A $0 here does not always mean a denial; on a service that went entirely toward your deductible, the plan pays nothing and you pay the whole allowed amount.

4. What you owe, or patient balance

The amount left for you. It is the allowed amount minus the plan's payment, broken down on many EOBs into deductible, copay, coinsurance and amounts not covered. CMS's guide says your bill from the provider should not be higher than this balance.

An invented EOB, read line by line

The EOB below is entirely hypothetical. The plan, provider, services and amounts are made up to show the arithmetic and are not prices. The invented plan has a $1,500 deductible, of which the patient had already paid $1,200 this year, 20% coinsurance after the deductible, and a $30 office-visit copay that does not count toward the deductible.

Line A: the visit is allowed at $128. The plan charges the $30 copay and pays the remaining $98. Nothing goes to the deductible, because this plan's copay services skip it.

Line B: the imaging study is allowed at $620. The patient still had $300 of deductible left, so the first $300 is theirs. The remaining $320 is shared at 20%: $64 for the patient and $256 for the plan. Patient total for the line: $364. This is the line where the deductible is met, which is why the next line looks different.

Line C: the lab panel is allowed at $42, and the deductible is already met, so the patient pays 20%, $8.40, and the plan pays $33.60.

Line D: the plan allowed nothing for a supply item, with a remark that it is included in another service. That remark matters: it means the plan treats the item as part of a different line's payment, and an in-network provider generally may not bill it to you separately. On a real EOB, read the remark's description at the bottom of the page and ask the plan to confirm.

The totals show what the claim did to the year. Of $2,085 billed, $790 was allowed. The plan paid $387.60, and the patient owes $402.40. The deductible is now met for the year, which changes the arithmetic on every later claim, as our guide to the deductible and the out-of-pocket maximum explains.

Reconciling the EOB with the provider's bill

Now the provider's bill arrives. In the hypothetical, the patient paid the $30 visit copay at the front desk. Here is what a correct bill should show, and two versions of a wrong one.

The correct bill: $2,085 minus the plan's $387.60, minus the $1,295 difference between billed and allowed, minus the $30 already paid, leaves $372.40. That is the EOB's $402.40 patient balance less the copay paid at the desk, exactly as CMS advises: the EOB does not show what you already paid, so subtract it yourself.

The early bill shows the full charge because the claim had not been processed when the statement was printed. Do not pay it; wait for the EOB, or call the provider and ask them to hold the account until the plan pays.

The bill with a problem is $85 higher than the correct one in the adjustment line, which is the $85 supply item the plan said was included elsewhere, and it has not credited the $30 paid at the visit. Its $487.40 balance is above the EOB's $402.40 patient balance. Under the CMS rule of thumb, that is the signal to call the provider's billing office with the EOB in hand.

The year-to-date box: your running totals

Many EOBs include a summary box near the top or bottom that shows how much you have paid toward your deductible and your out-of-pocket maximum so far in the plan year, often for you and for the family separately. It is easy to skip, and it is the most useful part of the document for planning. After the hypothetical claim above, that box would show the $1,500 deductible as met. From then on, covered in-network services under this plan cost the patient copays and 20% coinsurance until the out-of-pocket maximum is reached.

Check the box against your own records once or twice a year. If you paid a deductible amount on an earlier claim that does not appear in the running total, the plan may have applied it to the wrong family member or not yet processed a claim. A correction now changes what you owe on every later claim. If you are planning a procedure, the year-to-date figures are the starting point for estimating your share, which is why the plan's estimate and your own arithmetic should begin from the same totals.

A quick check before paying any medical bill

• Is there an EOB for this date of service yet? If not, ask the provider to wait for the claim to process.
• Does the patient balance on the EOB match the bill, after subtracting what you paid at the visit?
• Did the plan process each line as in network, if you used an in-network provider?
• Is any line marked denied, not covered, or awaiting information? Those are questions for the plan before payment.
• Are any lines marked as included in another service but still billed to you?
• Do the year-to-date deductible and out-of-pocket totals look right?

Six yes-or-no checks, in that order, catch the most common reasons a bill and an EOB differ. If every answer is clean, the bill is probably right, and the remaining question is how to pay it.

When the EOB and the bill disagree: who to call, in order

1. Check the dates and claim. Make sure the bill and the EOB cover the same date of service and provider. A bill can combine several visits; an EOB covers one claim.
2. Subtract what you paid. Copays and deposits paid at the visit are not on the EOB.
3. Call the provider if the bill is higher than the patient balance. CMS's advice is to talk to the provider. Ask them to explain each line that differs from the EOB and to correct the balance in writing.
4. Call the plan about coverage questions: a denied line, a remark you do not understand, or a service processed as out of network when you believe it was in network. Use the phone number on the EOB and the claim number.
5. Ask for the itemized bill if the provider's statement only shows a total. Our guide to checking an itemized bill for errors covers duplicates, wrong quantities and services you did not receive; for lab lines, the urine drug test bill guide shows how two codes on one date look on a statement and where the explanation of benefits shows what happened to each.
6. Negotiate or ask for assistance only after the amount is right. Once the balance matches the EOB, our guide to negotiating a hospital bill covers payment plans and reductions, and nonprofit hospitals must have a financial assistance policy.

Write down each call: the date, who you spoke to, and what they said. If a fix is promised, ask for the corrected statement in writing before you pay.

If the patient responsibility on the statement is higher than expected, the ten-cause guide to a high hospital bill ties each cause to the document where it shows. If a charge appears on a visit that was meant to be free, the guide on preventive visit charges explains the federal office-visit rule behind that line.

Remark codes and denials

CMS describes remark codes as short notes that explain charges or payments, with their meanings printed at the bottom of the EOB. They are the plan's reasons, and they are worth reading closely, because they tell you who to talk to. A few patterns recur on many EOBs, though the wording varies by plan:

• Applied to deductible or coinsurance: no action needed; the plan processed the line normally and you owe the share shown.
• Included in another service or bundled: the plan paid for this work inside another line. An in-network provider should not bill it to you separately. Ask the provider to remove it.
• Exceeds the allowed amount or contractual adjustment: the difference between billed and allowed. For in-network care, not your responsibility.
• Not covered, or not medically necessary, or no prior authorization: the plan denied the line. This is a coverage question for the plan, and you can usually appeal. Ask the plan for the reason and the appeal deadline in writing. The filing windows and steps for a denial are in how to appeal a health insurance denial.
• Out of network: different rules apply. Some out-of-network bills are protected by the No Surprises Act, such as emergency care. CMS lists the No Surprises Help Desk at 1-800-985-3059 for questions about those protections.
• Information requested: the plan is waiting for something, often from you, such as other-insurance information. The claim is not final; the bill should wait.

If a remark's description is unclear, ask the plan to explain it in plain language. A plan representative can see the full processing record for the claim, which the printed EOB summarizes.

The standard codes behind a remark: CO-45, PR-1 and the rest

Some EOBs print a short code such as CO-45 or PR-2 beside a line, and on the provider's side of the same claim, Medicare requires a code like that for every amount it does not pay. These codes come from two national lists that payers use on the electronic remittance advice they send providers, the HIPAA-standard ASC X12 835 transaction. The Medicare Claims Processing Manual, chapter 22, describes the set: a group code, which says who is financially responsible for an amount; a claim adjustment reason code (CARC), which says why the amount was adjusted; and, where needed, a remittance advice remark code (RARC), which adds detail a reason code cannot carry. The manual says the reason codes were developed for use by all U.S. health payers, and that the remark codes are maintained by CMS but may be used by any health plan when they apply.

Your EOB is a different document from the provider's remittance advice, and plans differ in what they print on it: an EOB may show the standard codes, the plan's own remark codes, or only words. If your EOB shows a plain-language remark you cannot follow, you can ask the plan which group code and reason code it applied to the line; the billing office will be looking at the same codes on its remittance.

The group code: whose amount is it?

The two letters before the number matter most. Chapter 22 lists three group codes for Medicare remittance advice. CO, Contractual Obligations, is used when a contractual agreement between the payer and the provider, or a regulatory requirement, caused the adjustment; the manual says these adjustments are generally a write-off for the provider and are not billed to the patient. PR, Patient Responsibility, is used when the adjusted amount may be billed to the patient, and the manual says it would typically be used for deductible and copay adjustments. OA, Other Adjustments, is used when no other group code applies. The X12 list also carries a fourth group code, PI, Payor Initiated Reduction, which is not one of the three on the Medicare list.

The same reason number can arrive with different group codes. CO-45 says the charge exceeded the contracted or fee schedule amount and the difference is the provider's to write off. PR-45 pairs the same reason with patient responsibility, so the plan is showing that difference as yours; if you used an in-network provider, that pairing is a question to put to the plan. The number tells you why; the letters tell you whose money it is. Read them together before deciding that a line is yours to pay.

Show the definitions behind this figure

Group code	Name	What chapter 22 says
CO	Contractual Obligations	A contract or regulation caused the adjustment; generally a write-off for the provider, not billed to the patient
PR	Patient Responsibility	The amount may be billed to the patient; typically deductible and copay
OA	Other Adjustments	Used when no other group code applies
PI	Payor Initiated Reduction	On the X12 list; not one of the three Medicare group codes

A selection of reason codes, in the list's own words

The full CARC list runs to hundreds of codes, and no public source ranks them by how often they appear on patient claims. The table below is a selection of codes that bear directly on what a patient owes or what to do next, with the description as the X12 list gives it (usage notes for billers left out). All were active on the list when checked on October 28, 2026.

Source: X12, Claim Adjustment Reason Codes list, descriptions copied without usage notes; Medicare Claims Processing Manual, chapter 22, section 60.2. Checked October 28, 2026. The last column is MyCarePrice's suggestion of where to start, not part of the code list.

Two cautions keep this table honest. First, the list changes. Chapter 22 says the reason and remark code lists are updated three times a year, on or around March 1, July 1 and November 1, and codes are retired. Code 15, which once covered an authorization number that was missing, invalid or did not apply, carries a stop date of May 1, 2018 on the X12 list. If a code on your EOB is not in a current list, ask the plan what it means. Second, the same reason code can be right or wrong depending on the facts. A 197 denial for a missing authorization raises the question of who was supposed to get it, which is covered in our guide to prior authorization before a procedure. A 50 or 204 denial is a coverage decision you can usually appeal, as the denial appeal guide explains.

EOB situations that need a second look

A claim for care you did not receive

An EOB for a provider or date you do not recognize is worth a call to the plan. Sometimes it is a separately billing lab or reading physician from a real visit. If it is not, report it to the plan, because the claim counts against your benefits.

Two plans

If you have coverage from two plans, each sends its own EOB, and the second plan's payment depends on the first plan's EOB. The patient balance on the first EOB may be paid partly by the second plan. Wait for both before paying.

A denial for the filing time limit

A line denied with reason code 29, which the X12 list words as "The time limit for filing has expired," means the claim reached the plan after its deadline. Read the group code in front of it: CO-29 marks the amount as the provider's write-off, while PR-29 assigns it to you and is worth a written question to the plan. Timely filing deadlines and who pays a late-filed claim sets out the Medicare, Medicaid and state limits and the order to check them in.

An EOB that says the plan paid you

Covered above under payee. The provider may bill you the full amount, and the plan's check is the money to pay it with.

An uninsured or self-pay visit

No EOB is produced when no claim goes to an insurer. For self-pay care, the comparison document is the Good Faith Estimate, and a bill $400 or more above it can open the federal dispute process described in our Good Faith Estimate guide.

Keeping EOBs useful

Most plans offer EOBs in an online account as well as by mail. Keep them for the year at least, grouped by date of service, next to the matching provider bills and receipts. They are the record of your deductible and out-of-pocket progress, the evidence for any dispute, and the substantiation an HSA or FSA administrator may ask for, as our HSA and FSA guide explains. Before a planned procedure, the same habit runs forward: get the plan's estimate in writing, and when the EOB arrives, compare it with that estimate as well as with the bill. The billing questions checklist covers what to ask before the date, and the medical bills guides cover everything after it.

Small lines from online care appear on the same statement. An e-visit for a portal message shows as code 99421, 99422 or 99423, and the portal message charge guide explains the seven-day rule behind it.

EOB answers in a sentence or two

If your EOB balance is right but the bill is still more than you can pay, the next step is asking the hospital about its financial assistance policy, which nonprofit hospitals must publish and which can reduce a correct balance.

What this guide relies on

• Centers for Medicare & Medicaid Services, Medical bill rights, Explanation of benefits guide: an EOB is not a bill, its contents, remark codes, "your bill should not be higher than the Patient Balance," payments not shown, who to call, No Surprises Help Desk 1-800-985-3059. Checked October 22, 2026.
• CMS, Medicare Claims Processing Manual, chapter 22, Remittance Advice, sections 40.6 and 60.1 to 60.3: the ASC X12 835 standard, the CO, OA and PR group code definitions, claim adjustment reason codes developed for all U.S. health payers, remark codes, and the three-times-a-year code list updates. Checked October 28, 2026.
• X12, Claim Adjustment Reason Codes (descriptions, start and stop dates, including the May 1, 2018 stop date for code 15) and Claim Adjustment Group Codes (CO, OA, PI, PR). Checked October 28, 2026.
• HealthCare.gov glossary, Allowed amount, including balance billing and the rule that a preferred provider may not balance bill for covered services. Checked October 22, 2026.
• HealthCare.gov glossary, Deductible, Coinsurance and Out-of-pocket maximum. Checked October 22, 2026.

Billing information with a hypothetical example. Not legal or insurance advice. Your plan's EOB and plan documents control.