Balance Billing vs Coinsurance: Which One Is on Your Bill

The hospital's statement says you owe $2,450. The explanation of benefits for the same claim, same date of service, same provider group, says your responsibility is $710. Neither document is lying. They are describing two different quantities, and only one of them is a ceiling anybody has to respect.

That gap is where most surprise-bill questions actually live. Not in whether the No Surprises Act exists, but in whether the number on the envelope in front of you is an unlawful balance bill or a perfectly ordinary deductible that happens to be large. The two look the same from across the room. On paper they come apart in about ten minutes, using four things: the EOB's adjustment lines, the two-letter group code in front of each one, the remark codes at the bottom, and one subtraction.

Everything cited below was read on 20 September 2026. The regulation text came out of the eCFR versioner API for the 1 September 2026 edition of title 45, not a summary of it; the code definitions came from the current lists at x12.org. I am not a lawyer and I do not work in billing, which is exactly why the citations are here — check the numbers against the source rather than against me.

Two documents, two ceilings

The provider's statement answers one question: what is left after the plan paid. It is charges minus payments received. Nothing in that subtraction knows anything about your benefits, and nothing in it is constrained by federal law.

The EOB answers a different question: what the plan decided you are responsible for. Those are the lines marked deductible, coinsurance and copay, and under the federal balance billing rules that total is a legal maximum rather than a suggestion. For emergency services, 45 CFR 149.410(a) says a nonparticipating emergency facility and a nonparticipating provider "must not bill, and must not hold liable" the patient for an amount "that exceeds the cost-sharing requirement for such services." For non-emergency care from an out-of-network provider at a participating facility, 149.420(a) uses the same construction.

Must not hold liable is the phrase worth noticing. It is not only about sending the bill. A provider that keeps the amount on a statement, refers it to collections, or asks you to sign for it at a follow-up visit is holding you liable for it.

So the comparison is this: the patient-responsibility total on the EOB, against the balance on the statement. If the statement is larger and the visit is one of the protected situations, the difference is the disputed amount and you can name it to the dollar. Which situations are protected, and the several that are not, is a separate piece of homework: No Surprises Act: What It Covers and What It Leaves Out. Everything here assumes you already landed inside the protection and are trying to check the math.

The number that sets the ceiling is not the billed charge

Here is the part that catches people, and the reason a $2,890 charge can produce a $710 ceiling.

Your plan does not calculate your cost sharing against what the provider charged. It calculates it against the recognized amount. In a state without a specified State law, that term is defined at 45 CFR 149.30 as the lesser of the qualifying payment amount or the amount billed by the provider or facility. The qualifying payment amount, or QPA, is broadly the plan's median contracted rate for that service code in that region, computed under the long methodology at 149.140.

Then the coverage rule does the rest. The plan must not impose cost sharing greater than the in-network requirement, and must calculate it "as if the total amount that would have been charged for the services by such participating provider or participating emergency facility were equal to the recognized amount for such services" (149.110(b)(3)(ii) and (iii), emergency services). 149.120(c)(1) and (2) does the same for the non-emergency case, in the same words. Your deductible and coinsurance run against the recognized amount and stop there.

One more clause that tends to get left on the table: whatever you do pay has to be counted toward your in-network deductible and in-network out-of-pocket maximum, in the same manner as if a participating provider had furnished the care (149.110(b)(3)(v), 149.120(c)(5)). If your plan posted the payment to the out-of-network deductible instead, that is its own error, and it is worth checking on the same afternoon, because it silently changes every claim that follows this one.

Running it on a real claim

Numbers move faster than definitions here. Take an emergency department visit where the physician group was out of network, and a plan with a $1,500 in-network deductible of which $900 was already met, then 20% coinsurance.

The $710 is the number the EOB should show as your responsibility, and the number the provider is barred from exceeding. The $1,740 is not a discount you are asking for. It is an amount the regulation says cannot be billed to you or held against you. And the $600 of that $710 that went to the deductible closes out your in-network deductible for the year, which is worth confirming on the next EOB that arrives.

Two footnotes on the arithmetic. If the provider had billed less than the QPA — say $900 against a QPA of $1,150 — the recognized amount would be the $900, because the definition takes the lesser of the two. And the recognized amount is not the same thing as the out-of-network rate, which is what the plan actually pays the provider and what open negotiation or the federal dispute resolution process gets fought over. Your ceiling is keyed to the recognized amount. A later determination that raises the plan's payment does not raise your share.

The remark codes that say which rule the plan used

This is where an EOB stops being a receipt and starts being evidence. X12 maintains a set of remittance advice remark codes written specifically for these claims, and they are unusually blunt. From the current remittance advice remark code list, read 20 September 2026:

• N864 — the claim is subject to the No Surprises Act provisions that apply to emergency services.
• N865 — subject to the provisions for non-emergency services furnished by nonparticipating providers during a visit to a participating facility.
• N862 — member cost share "is in compliance with the No Surprises Act, and is calculated using the lesser of the QPA or billed charge."
• N869 — cost sharing was calculated based on the qualifying payment amount.
• N870 — cost sharing was based on the billed amount because the billed amount was lower than the QPA.
• N867 — cost sharing was calculated based on a specified state law.
• N882 — the payment and cost sharing were based on the plan's allowance "because the provider or facility obtained the patient's consent to waive the balance billing protections."
• N878 and N879 — the provider said it had notice and consent, but it was not obtained in a manner consistent with federal law (N878) or is not permitted for these services at all (N879), and therefore "balance billing is prohibited."

Any of N864, N865, N862, N869, N870 or N867 on a claim is the plan telling you, in writing, that it processed the claim under the balance billing rules. N878 and N879 are stronger still: they are the plan saying a consent form was waved at it and did not work.

The code that does the most work is N830, which predates the others and covers state and federal balance billing rules generally. Amounts identified with OA, CO or PI "cannot be collected from the member," and "any amount the provider collected over the identified PR amount must be refunded to the patient within applicable Federal/State timeframes." That second clause is the whole difference between disputing a charge and asking for money back, and it is a practical argument for settling the statement before paying it rather than after.

Now the disappointing part, worth knowing before you go hunting. Your EOB is not required to carry any of this. 45 CFR 149.100, the rule that mandates CARC and RARC codes on these claims, applies when a plan sends remittance advice "to an entity (other than a participant, beneficiary, or enrollee)." The patient is written out of the sentence. Same with the QPA: where the recognized amount is the QPA or the billed amount, 149.140(d)(1) requires the plan to hand the QPA for each item or service to the provider, with each initial payment or notice of denial of payment. Plenty of plans pass the codes through to the member EOB anyway. When yours has not, the document you want is the provider-facing remittance advice for your claim, and the route to it is the claim file request: Insurance Claim File: How to Request It, and From Whom. Name the remittance advice and the 149.140(d) disclosure in the request instead of asking for "everything in the file."

The two-letter group codes — PR, CO, OA, PI — come off a third and much shorter list, and they decide by themselves whether an adjustment can travel to you. If those letters are unfamiliar on your paperwork, they are unpacked here: CARC and RARC Codes: What They Mean on Your EOB.

Same gap, different reason

The reason all of this is confusing is that the arithmetic is identical in cases with opposite answers. Take a $420 charge with a $190 allowed amount, twice.

Out-of-network dermatologist, scheduled, in an ordinary office. The plan pays 60% of the $190 allowed, or $114, and your coinsurance is $76. The practice bills $420 − $114 = $306. Your EOB says $76. The extra $230 is a balance bill, and federal law does not forbid it: a physician office that is not a hospital outpatient department is not one of the four facility types listed at 149.30, and you chose the provider. You can try to negotiate it. You are negotiating, though, not enforcing, and the difference shows up the moment somebody says no.

In-network specialist, same charges. The plan pays $114, your coinsurance is $76, and the $230 is a contractual write-off the practice agreed to when it joined the network. If it bills you anyway, the $230 is still not yours, but for a different reason and with a different remedy: that is a network contract problem, and it goes to your plan's provider relations or network department, not to HHS. On an EOB it usually appears as adjustment reason code 45 — "charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement" — carrying a CO group code. Code 45 is one of the reason codes that can legitimately appear as either CO or PR depending on who is liable, which is exactly why the number alone proves nothing and the two letters in front of it prove a great deal.

Same $230 gap, then, and three possible statuses: barred by federal regulation, barred by contract, or genuinely owed. The EOB alone does not tell you which. Where the service was furnished, and the network status of each rendering provider on the claim, does.

Where the arithmetic is set by your state instead

The recognized amount definition has a branch in it. In a state with a specified State law in effect — a state law that supplies its own method for determining the total amount payable for out-of-network services — the recognized amount is whatever that law produces, not the lesser of QPA and billed charge. A third branch covers states operating under an All-Payer Model Agreement. Both sit in the same definition at 149.30, and on the remittance side they surface as N867 and N868.

Rules differ from state to state, and the only reliable answer is your own state's. Three ways to find it without guessing:

1. Look for N867 on the claim. If the plan itself says cost sharing was calculated under a specified state law, that is the plan's own characterization of which regime applied to your money.
2. Read the out-of-network section of your plan materials for an opt-in statement. A plan that opts into a state law — the opt-in exists for plans not otherwise subject to state insurance law, which in practice means self-funded ones — must, in the words of the definition at 149.30, "prominently display in its plan materials describing the coverage of out-of-network services a statement that the plan has opted into the specified State law," identify the relevant state, and generally describe the services covered. If that paragraph exists, it is in the governing plan document rather than the benefits summary, so ask for the plan document by name.
3. Ask your state's department of insurance what its balance billing statute covers and whom it reaches. Most state laws reach fully insured coverage and not self-funded employer plans, so the funding question decides whether the state answer is yours at all: Self-Funded vs Fully Insured: How to Find Out for Sure.

Who enforces is a separate question from which rule applies, and the two get confused. CMS's consumer protections enforcement page, read 20 September 2026, states that as of 1 May 2026 four states — Missouri, Tennessee, Texas and Wyoming — had notified CMS that they do not have the authority to enforce, or are not otherwise enforcing, the ACA market reform provisions. Read what that list is. It records who does the enforcing of one body of insurance law. It is not a list of states where the balance billing ceiling stops applying, and it is not the same list as the states where CMS has stepped in on the No Surprises Act specifically: the same page says CMS takes over the NSA requirements that apply to providers and facilities in a state where it determines the state is not substantially enforcing them, which is a separate determination made requirement by requirement. If you live in one of the four, 149.410 and 149.420 still set your ceiling and the federal complaint route below is still yours. What changes is which office answers the phone.

Bills that look like violations and are not

Four common ones, worth ruling out before you write anything.

The statement arrived before the plan finished. A plan has 30 calendar days after the bill is transmitted to determine coverage and send the provider either an initial payment or a notice of denial of payment, and that 30-day period starts on the date the plan receives the information it needs to decide the claim (149.110(b)(3)(iv)(A), 149.120(c)(3)). A statement showing the full charge with "insurance pending" inside that window is a statement, not a balance bill.

The plan and the provider are still arguing. After the initial payment, a provider generally has 30 business days of open negotiation and then about 4 business days to initiate the federal dispute resolution process (149.140(d)(1)(iv), 149.510(b)(1)(i)). That fight runs between them. It does not move your ceiling.

The number is your deductible, and the deductible is simply large. A $1,500 line carrying reason code 1 with a PR group code on a protected claim is not a violation. It is a $1,500 deductible. The test is whether the statement exceeds the patient-responsibility total, not whether that total is uncomfortable.

The service was denied as not covered. An adjustment marked with reason code 96, non-covered charges, is a coverage decision, and a coverage decision is an adverse benefit determination with its own appeal deadline running from the day the notice was issued. A billing complaint does nothing to it. Different track, different calendar, and the appeal deadline does not pause while the billing argument runs.

The letter, and the date

If the statement exceeds the EOB's patient-responsibility total on a protected claim, one letter to the billing office does the whole job. Ask for three things: an itemized bill, the remittance advice for the claim including the qualifying payment amount disclosed under 45 CFR 149.140(d)(1), and — if anyone says you signed something — a copy of the signed notice and consent document. It has to carry the time and date the notice was received and the time and date the consent was signed (149.420(e)(3)), so ask for those by name rather than for "the form." Whoever took that consent has to keep it for seven years under 149.410(d) and 149.420(h), so "we no longer have it" is not an answer.

Then put the arithmetic in a single sentence, because a billing office can act on a sentence with a dollar figure in it and cannot act on a grievance. Something in this shape:

Under 45 CFR 149.410(a)(2), the amount I may be billed for the emergency services furnished on 3 August 2026 is limited to my in-network cost sharing. My plan's explanation of benefits for claim 24-7719004 states that amount as $710. Your statement dated 11 September 2026 shows a patient balance of $2,450. Please correct the account to $710 and confirm the correction in writing.

Two dates go on the calendar today. The first is 30 calendar days from the date the provider says it sent the claim to your plan — before that runs out, an unpaid statement is not yet evidence of anything. The second is 30 days from the day you send the letter, as the point where you stop waiting: the No Surprises Help Desk takes complaints at 1-800-985-3059 and online through cms.gov/medical-bill-rights, and HHS acknowledges receipt no later than 60 business days after a complaint arrives.

Hold the disputed portion while that runs — hold it because the patient-responsibility total on the EOB says so, not because the statement looks large. An unpaid balance on a claim that turns out not to be protected goes to collections like any other, which is why the four cases above come before the letter. Once the money has moved, N830's refund language is what you are leaning on, and getting a correction is a phone call while getting a refund is a campaign.