How to read an EOB (and tell what you actually owe)

An explanation of benefits, or EOB, is the statement your health insurer sends after it processes a claim. A provider treats you, the provider files a claim with your plan, the plan decides what it will and won't pay, and the EOB is the plan's report of that decision. The single most important thing to know about it is printed on most of them: an EOB is not a bill. You're not meant to pay from it. The provider sends a separate bill for whatever you owe, and per the federal Centers for Medicare & Medicaid Services you usually get the EOB before that bill arrives. So the EOB is really a preview: it tells you, ahead of time, what the bill should say.

You'll find EOBs in your insurer's member portal or app, usually under a tab like Claims or Statements, and most plans still mail paper copies. The reason an EOB feels unreadable is that it crams a claim into a grid of charges, allowances, and short letter-and-number codes that look like a bill demanding the biggest number on the page. It isn't. Almost every EOB, from any insurer, is built from the same parts: a header (your name, member ID, the claim number, the provider, and the date of service), a row or two of money columns for each service, a column of adjustment codes, and a legend at the bottom that translates them. Learn the columns and the codes and the whole thing resolves into a simple question with a clear answer: of everything here, what do I actually owe?

The rest of this guide answers that question in order: the money columns, why you owe anything at all, the codes that tell you who's responsible for each line, how to check the EOB against the bill, and what to do when a claim comes back denied. For a field-by-field reference on the document itself, the explanation of benefits page defines every line and cites its sources.

Read the four money columns

Strip away the header and the codes and an EOB is just a few dollar figures per service. They almost always run in the same order, and the order is the whole trick, because each number is derived from the one before it.

Hover or tap any line to see what it means.

The reassuring part is the math. For an in-network service it works like this:

• Amount billed minus the allowed amount is the provider's write-off. Your in-network provider agreed to accept the allowed amount as full payment, so the difference, often labeled the plan discount or network savings, is money nobody pays. It exists only to show you how much the negotiated rate saved you off the sticker price.
• The allowed amount minus what the plan paid is your responsibility. That remainder is your deductible, coinsurance, and copay, and it's the only number on the EOB you might owe.

This is why the giant "amount billed" figure at the top is the wrong number to panic over. A $2,400 charge that the plan allows at $700 and pays $560 on leaves you a $140 responsibility, not $2,400. Read the columns left to right and the page tells you a story about a number shrinking, ending at the only one that matters.

One caveat that the next sections build on: this clean write-off math is an in-network promise. When a provider is out of network, the gap between billed and allowed isn't always a write-off. Sometimes the provider can bill it to you, which is the surprise-bill problem we'll come back to.

Why you owe anything at all

If the plan covers the service, why is there a "patient responsibility" number at all? Because almost no plan pays 100% from the first dollar. Your share is built from a few standard pieces, and the EOB assembles them into that final figure. These four terms explain essentially every dollar you'll ever owe on an EOB:

The one that confuses people most is coinsurance, because it's a percentage and the EOB calculates it on the allowed amount, not the billed charge. Twenty percent of a $700 allowed amount is $140, even though the provider's sticker price was $2,400. If you compute your coinsurance off the big number, you'll always think you've been overcharged. Compute it off the allowed amount and it ties out.

Two notes that save confusion. First, your premium, the monthly amount you pay to have coverage, is never on an EOB. The EOB is about one claim, not your ongoing cost of insurance. Second, many EOBs print your running deductible and out-of-pocket maximum progress somewhere on the page. That's worth finding, because it's the same data that tells you when your plan flips to paying 100%, and it's a quiet reason to keep your EOBs in one place across the year instead of tossing each one.

The codes, and the one that tells you who owes

The codes are the part every other guide skips and the part that actually decides what you pay. Each adjusted line carries a short code, and the legend at the bottom of the EOB spells it out in fine print. These are standardized: the industry calls them Claim Adjustment Reason Codes (CARC), sometimes with a supplemental Remittance Advice Remark Code (RARC) adding detail. They're maintained by a standards body called X12 and used on everything from a commercial EOB to a Medicare notice, which is why they're worth learning once.

Here's the insight that does the most work: a two-letter prefix in front of the number tells you who is responsible for that line. Read the prefix before you read anything else.

That single distinction answers the question the whole EOB is really about. A line marked CO is the provider's contractual obligation, so you don't owe it, no matter how large it looks. A line marked PR is patient responsibility, so it's a candidate for your bill. The federal government is explicit about this for Medicare: a beneficiary may be billed only when the PR group code is used. The same logic holds on commercial plans.

The numbers then say why. You'll see the same handful again and again, so here are the common ones in plain English, with whether they're typically yours to pay:

Notice the pattern: the codes for things you owe (1, 2, 3) are your deductible, coinsurance, and copay, and they ride a PR prefix. The biggest, scariest code, 45, is usually the write-off, and it rides a CO prefix, meaning it's not yours. Several codes (50, 96, 204) can go either way, which is exactly why the prefix is the first thing to read: the number names the reason, the prefix names the payer. When a line says the claim "lacks information" (16) or is a "duplicate" (18), that's the provider's billing problem to fix, not a charge for you to pay.

Match the EOB to your bill

Reading the EOB and reconciling it against the provider's bill are two different things, and the second is where you actually catch money. The rule is simple, and CMS states it plainly: your provider's bill should not be higher than the patient-responsibility figure on your EOB. If it is, something is wrong, and you found it before you paid for it. The cross-check takes about two minutes:

1. Wait for the EOB before you pay any bill. Because the EOB usually arrives first, a bill that shows up ahead of it is the most common reason the numbers don't line up yet.
2. Get the itemized bill, not the summary. A one-line "amount due" can't be checked against anything. Ask the provider for the itemized version that lists each service.
3. Match each line by service and date, then compare the bill's "you owe" to the EOB's patient responsibility for the same service. They should be equal.
4. Flag the gap. If the bill is higher, the usual suspects are a charge billed before the claim finished processing, a duplicate, a coding error, or a balance bill (next section). Don't pay the difference until it's explained.

This matters more than it sounds. In ACA marketplace plans, insurers denied roughly 19% of in-network claims in 2024, according to a March 2026 analysis from KFF, and a denied or mis-paid line is precisely the kind of thing the EOB-versus-bill check surfaces. The catch is having both documents in one place when the bill lands weeks later. That's the ordinary work software is good at: when Granite reads an EOB, it pulls out the carrier, the claim number, and the patient-responsibility figure, so the EOB is already sitting next to the bill when you need to compare them, and you can ask what you owed for a given visit instead of digging through a drawer.

When a claim is denied, the EOB starts a clock

A denied line on an EOB isn't the end of the conversation. It's the start of one, and it's the document that starts it. HealthCare.gov tells consumers to look at the EOB to find how to challenge a denial, because the denial notice and your appeal deadline live right there. The reason this is worth your attention is a striking pair of numbers: insurers deny about one in five in-network marketplace claims, but fewer than 1% of those denials are ever appealed, and of the appeals that are filed, insurers still overturn enough that roughly a third succeed (KFF, 2024 data). Appealing is rare, and it works often enough to be worth it.

Most denials aren't even about whether you needed the care. In 2024, only about 5% were for "lack of medical necessity"; the rest were administrative, things like missing information or a missed prior authorization. Many of those are fixed with a phone call to the provider's billing office, asking them to correct and resubmit, before you ever file a formal appeal. When the denial is real and you disagree with it, you have two layers of appeal, each with a fixed deadline:

The first layer is the internal appeal, where you ask the plan to reconsider; the second is the external review, where an independent reviewer outside the insurer makes the call, and the plan is legally bound by the result. The dates are counted from the denial, which is one more reason to read the EOB when it arrives rather than months later. None of this is legal advice, and your plan's own rules may give you more time than the federal floor, but the instinct is the same as with any deadline: the people who read the notice on time keep their options open.

Surprise bills, balance billing, and your rights

Sometimes the gap between billed and allowed isn't a write-off you can ignore. Balance billing is when an out-of-network provider bills you for that difference, the part your plan didn't cover, on top of your normal cost-sharing. It's how people end up with a four-figure bill for an emergency they had no way to shop for.

Since January 2022, the federal No Surprises Act bans the worst version of this. You can't be balance-billed, and can't be charged more than your in-network cost-sharing, for three big situations: emergency services, care from an out-of-network provider at an in-network facility (the anesthesiologist or radiologist you never chose), and out-of-network air ambulance. If an EOB or bill tries to charge you the out-of-network balance for one of those, that's the protection to invoke. One honest gap to know: the law does not cover ground ambulance, which remains a common source of surprise bills, so that one you still have to watch.

If you're uninsured or paying cash, you have a different protection: a Good Faith Estimate of what care will cost up front. If the final bill comes in at least $400 over that estimate, you can dispute it through a federal process, generally within 120 days of the bill. As always, the EOB or estimate is the document that anchors the dispute, which is one more reason to keep it.

If you're on Medicare, your EOB has a different name

Medicare paperwork trips people up because the document depends on which kind of Medicare you have. If you have Original Medicare (Parts A and B), you don't get an EOB at all. You get a Medicare Summary Notice (MSN), sent by Medicare itself at least twice a year, listing the claims it processed in that stretch. If you have a Medicare Advantage (Part C) or Part D drug plan, the private plan sends you an EOB instead, often monthly.

The good news is that everything above still applies. An MSN and a Medicare EOB are both notices, not bills, and both use the same adjustment-code system, so the CO-versus-PR rule for telling what you owe reads exactly the same way. The only real differences are who mails it (Medicare or your plan) and how often. Note that the MSN's "every six months" schedule is the current one on Medicare's own site, even though plenty of older guides still call it quarterly.

How long to keep an EOB

Once you've read an EOB and matched it to the bill, it still has a job. Keep an ordinary EOB for about a year after the matching bill is paid and reconciled. Keep it longer, three to seven years, if it backs up a tax deduction, substantiates an HSA or FSA withdrawal, relates to ongoing or chronic treatment, or is tied to an open appeal or dispute. An EOB is your proof of how a claim was paid and what you actually owed, and those questions can resurface long after the visit. For where EOBs sit among everything else, how long to keep important documents has the full table.

The practical catch is the same one that bites with statements and tax forms: an EOB carries your member ID, claim numbers, and a record of your care, so it isn't a document to leave in an email inbox or a shared drive, and your insurer's portal keeps only a limited window of them. Download the PDFs, and store them somewhere that's both findable and encrypted at rest.

That's the whole document: four money columns, a cost-share that explains your share, and a set of codes whose two-letter prefix tells you who owes. Granite reads and files the EOBs you already have, pulls out what you owed on each one, and lets you ask about your own claims with a citation back to the line. It isn't your insurer and can't appeal a claim or dispute a charge for you, and it isn't medical or legal advice. But an EOB lives in a much larger pile of records, and if you're keeping the whole family's straight, organizing medical records at home is the next thing to read. The same skill you just used, reading the lines instead of the total and checking what you're told you owe, is exactly what you'd use on a bank statement.