Explanation of Benefits (EOB)

An explanation of benefits is the statement a health plan or insurer sends to a member after it has processed a claim. It sets out the provider's charge, the amount the plan treated as the price, what the plan paid, and what it says the member owes. It is not an invoice, and the amount it shows as the member's responsibility is the plan's calculation rather than a demand for payment; the bill, if there is one, comes from the provider.

The naming is worth settling, because the phrase does different work in different places. For a Medicare Part D plan it is an operative regulatory term: 42 C.F.R. 423.128(e) provides that a Part D sponsor "must furnish directly to enrollees, in the manner specified by CMS and in a form easily understandable to such enrollees, a written explanation of benefits when prescription drug benefits are provided under qualified prescription drug coverage", and then lists what it must contain. For an employer plan or a commercial policy the title is a market convention, and federal law approaches it from the other end: it prescribes what a plan must communicate rather than what to call the envelope. What it requires there is a notification of an adverse benefit determination under the ERISA claims procedure regulation, and the explanation of benefits is generally the document through which a plan delivers it. Federal law does legislate onto the document once it exists, which is a useful sign of how settled the convention is: 42 U.S.C. 300gg-115(c) requires plans to "include on each explanation of benefits" the disclosure about patient protections against balance billing. That distinction is not pedantry: it is why a document most people file unread carries legal content and starts a clock.

A partial payment is a partial denial, and the regulation says so in terms. 29 C.F.R. 2560.503-1(m)(4)(i) defines an adverse benefit determination as "[a] denial, reduction, or termination of, or a failure to provide or make payment (in whole or in part) for, a benefit", expressly including a determination resulting from utilization review and a failure to cover something as experimental, investigational or not medically necessary. In whole or in part. So an explanation of benefits reporting that the plan paid less than was claimed is not merely informational, and the paragraph most people skip is the one that matters.

What that notification must contain. Paragraph (g)(1) requires the plan administrator to provide written or electronic notification of any adverse benefit determination setting forth, in a manner calculated to be understood by the claimant: "(i) The specific reason or reasons for the adverse determination; (ii) Reference to the specific plan provisions on which the determination is based; (iii) A description of any additional material or information necessary for the claimant to perfect the claim and an explanation of why such material or information is necessary; (iv) A description of the plan's review procedures and the time limits applicable to such procedures, including a statement of the claimant's right to bring a civil action under section 502(a) of the Act following an adverse benefit determination on review". Two further items apply to group health plans. Under (g)(1)(v)(A), where an internal rule, guideline or protocol was relied on, the plan must give either that rule or a statement that it was relied on and that a copy will be provided free of charge on request. Under (g)(1)(v)(B), where the determination rests on medical necessity, an experimental treatment exclusion or a similar limit, the plan must give either an explanation of the scientific or clinical judgment applying the plan's terms to the claimant's medical circumstances, or a statement that such an explanation will be provided free of charge on request. And under (g)(1)(vi), where an urgent-care claim is involved, a description of the expedited review process.

The practical translation. A one-line denial code is not compliance. If an explanation of benefits says a service was not medically necessary and stops there, the regulation entitles you to ask for the clinical reasoning applied to your own circumstances, and to receive it without charge. That request is frequently the fastest way to find out whether a denial was a coding problem, a missing prior authorization, or a genuine coverage dispute, and it is information the plan is obliged to have before it can deny on that ground.

Medicare Part D's version is prescribed rather than customary. Section 423.128(e) requires the explanation of benefits to list the item or service paid for and the amount of payment for each; to include notice of the enrollee's right to request an itemized statement; to show cumulative year-to-date benefits provided against the current year's deductible and the annual out-of-pocket threshold; to show cumulative year-to-date incurred costs so far as practicable; to give, for each prescription drug claim, the cumulative percentage increase in the negotiated price since the first claim of the benefit year together with therapeutic alternatives carrying lower cost sharing where the plan has identified them from the formulary; to include any negative formulary changes applicable to the enrollee; and to arrive no later than the end of the month following any month in which benefits were provided. The price-increase and cheaper-alternatives items are the ones worth actually reading, because they are the only routine notice most enrollees get that a drug they are already taking has become more expensive or that a substitute exists.

Original Medicare sends a different document under a different name. For Part A and Part B claims, what arrives is the Medicare Summary Notice, and the underlying regulation calls it a notice of initial determination. 42 C.F.R. 405.921(a)(2) requires it to contain the reasons for the determination, including whether a coverage determination or medical review policy was applied; the procedures for obtaining further information about the determination; and information on the right to a redetermination together with instructions for requesting one. So the same idea, with its own name, its own content list and its own appeal vocabulary.

And the version that was supposed to arrive before the care. The No Surprises Act required plans to send an advance explanation of benefits after a provider notifies them of scheduled care, so that a patient could see the expected cost in advance rather than the actual cost afterwards. Enforcement was deferred before the requirement took effect, pending rulemaking on the data standards it needs, and the No Surprises Act page carries the current status. So the one version of this document that would arrive in time to change a decision is the one nobody receives.

1. The provider submits a claim to the plan after the care.

2. The plan processes it against the contracted or determined price and its coverage rules.

3. The plan issues the explanation of benefits, showing the charge, the amount allowed, the amount paid and the member's responsibility.

4. Anything denied or reduced makes it an adverse benefit determination, and the notification must state the reason, the plan provision, what else is needed, the review procedure and its time limits.

5. You compare it against the provider's itemized bill. Disagreement between the two is the commonest sign of an error.

6. You appeal within the plan's stated time limits if the determination is wrong, requesting the internal rule or the clinical rationale first if the denial turned on either.

A hypothetical, reading two lines of one statement. A clinic bills $1,180 for a visit. The explanation of benefits shows an allowed amount of $400, a plan payment of $320, and patient responsibility of $80. The $1,180 − $400 = $780 difference is written off by the in-network provider and is not owed by anyone. That line is arithmetic, and it is doing what it should.

The second line is an MRI billed at $2,300. The plan paid $0 and the reason code reads "not medically necessary", leaving patient responsibility of $2,300.

That line is an adverse benefit determination, and three obligations attach to it. The notification must give the specific reason and the plan provision it rests on. It must describe the review procedure, its time limits, and the right to bring a civil action after review. And because the denial turns on medical necessity, the plan must either explain the scientific or clinical judgment applied to these circumstances or state that it will provide that explanation free of charge on request. Asking for it costs nothing, and the answer usually reveals whether the problem was a missing prior authorization, a coding error, or a real dispute about the care.

What it does for you

• It shows the allowed amount and the write-off, which is the only place most patients ever see what care actually cost as against what was charged.
• It arrives before the provider's bill often enough to catch an error while it is still cheap to fix.
• Wherever something was denied or reduced, it must state the reason and the plan provision, which turns a vague refusal into something answerable.
• It carries the review procedure and the time limits, so the appeal deadline is on the document rather than somewhere in a plan booklet.
• For a Part D enrollee, it is the routine notice that a drug's negotiated price has risen and that a cheaper alternative on the formulary exists.

What is wrong with it

• It arrives after the care, so it informs a decision that has already been made.
• The layout is not standardized across insurers, and the same fields carry different labels from plan to plan.
• Reason codes are frequently terse to the point of uselessness, and the right to a fuller explanation has to be exercised rather than delivered.
• The patient responsibility figure is easily mistaken for a bill, which produces both duplicate payments and ignored real bills.
• The advance version, which would have solved the timing problem, has been unenforced since before it took effect.