Third party billing is a payment arrangement in which someone other than the person receiving a service pays the provider directly for it. In health care, that someone is usually your insurer, a government program like Medicare or Medicaid, or in some cases an employer. You get the care, the provider sends the bill to the payer, and you’re left owing only whatever cost-sharing your policy requires. The structure appears in corporate logistics and government grants too, but almost everything confusing about it comes from medical billing, so that’s where this guide stays.
The arrangement has three roles. The provider delivers the service and submits the claim. The recipient (you, the patient) uses the service. The payer is the entity contractually obligated to cover the bulk of the cost. The defining feature is that separation: the entity writing the check is not the entity that got the care.
Where You’ll Encounter Third Party Billing
Health insurance is the dominant setting. Commercial carriers and government programs reimburse providers using standardized claim forms, negotiated rates, and coverage rules that decide what gets paid.
The same basic structure runs elsewhere. Companies authorize vendors to bill corporate accounts for services performed for employees under a master services agreement. Federal and state agencies pay vendors directly for services delivered to grant beneficiaries, with documentation required before funds release. The mechanics of claim submission, adjudication, and appeals that follow are specific to healthcare, but the three-role shape is the same anywhere a contract shifts the payment obligation off the service recipient.
Prior Authorization Can Come First
For many services the billing cycle starts before you ever see the provider. Prior authorization is the payer’s requirement that a provider get advance approval before performing certain procedures, prescribing specific drugs, or admitting you to a facility. Skip this step and the payer can deny the claim entirely, leaving you with a bill for a service your insurance would otherwise have covered.
Starting January 1, 2026, a federal rule requires certain payers in Medicare, Medicaid, and marketplace programs to answer prior authorization requests within set timeframes: 72 hours for urgent requests and seven calendar days for standard ones.1Centers for Medicare & Medicaid Services. CMS Interoperability and Prior Authorization Final Rule (CMS-0057-F) The deadlines don’t cover every insurer, but they set a direction.
How a Claim Moves Through the System
Submission
After providing care, the provider sends a standardized claim to the payer. The claim includes procedure codes (what was done) and diagnosis codes (why it was medically necessary).2Centers for Medicare & Medicaid Services. Professional Paper Claim Form (CMS-1500) Each payer sets a filing deadline, commonly 90 days to one year from the date of service.
If the provider misses that deadline, the consequences fall on the provider, not you. Under Medicare, a provider who files late generally cannot charge you more than the deductible and coinsurance you would have owed had the claim been processed normally. Private insurer contracts often say something similar. If you get a bill for a service your provider failed to submit on time, push back.
Adjudication
The payer then reviews whether you were eligible on the date of service, whether the service was medically necessary, and whether it falls within your benefits. Out of that review comes the “allowed amount,” which is the maximum the payer will recognize for the service. It comes from the contract between payer and provider and is almost always lower than the provider’s listed price. The gap between the listed price and the allowed amount is a contractual adjustment: neither you nor the payer owes it.
Explanation of Benefits and Payment
After adjudication you get an Explanation of Benefits (EOB) showing what was billed, what the payer covered, and what you owe. An EOB is not a bill.3Centers for Medicare & Medicaid Services. How to Read an Explanation of Benefits It’s an informational statement. The provider gets a parallel document called a Remittance Advice detailing what the payer paid, denied, or adjusted, and then bills you for whatever remains your responsibility.
Keep every EOB. If you ever dispute a charge, the reason codes on the EOB are your starting point: they tell you precisely why a line was handled the way it was.
What You Still Owe
Third party billing is not free care. Your policy’s cost-sharing provisions set what you owe out of the allowed amount.
- Deductible: the amount you pay each year before the payer starts covering most non-preventive services.
- Copayment: a flat fee at the time of certain services, like a set dollar amount for an office visit or a prescription.
- Coinsurance: a percentage of the allowed amount you pay after meeting your deductible. At a 20% coinsurance rate on a $1,000 allowed amount, you owe $200.
These costs don’t stack without a ceiling. Under the Affordable Care Act, marketplace plans cannot set an annual out-of-pocket maximum higher than $10,600 for an individual or $21,200 for a family in 2026.4HealthCare.gov. Out-of-Pocket Maximum/Limit Once your deductibles, copayments, and coinsurance hit that ceiling, the plan covers 100% of additional in-network costs for the rest of the plan year. Employer plans are subject to similar caps. In a year with a major procedure, tracking spending against that number tells you when further in-network care should cost you nothing.
Balance Billing and the No Surprises Act
Balance billing happens when an out-of-network provider charges you the difference between their full price and your insurer’s allowed amount. If a surgeon’s listed charge is $10,000 and the plan’s allowed amount is $6,000, the surgeon tries to send you a bill for $4,000. That practice drove the worst surprise medical bills in the country until federal law intervened.
p>The No Surprises Act prohibits balance billing in three situations: emergency services from out-of-network providers or facilities, non-emergency services from out-of-network providers at in-network facilities, and air ambulance services from out-of-network providers.5Centers for Medicare & Medicaid Services. The No Surprises Act’s Prohibitions on Balance Billing In those protected situations you owe only your in-network cost-sharing amount, and the provider and insurer settle the rest between themselves.6eCFR. 45 CFR 149.410 – Balance Billing in Cases of Emergency Services
There is one exception. For certain non-emergency services at in-network facilities, an out-of-network provider can ask you to waive your balance billing protections by signing a notice-and-consent form. The provider must give you a good-faith cost estimate and present the consent form separately from other paperwork, at least 72 hours before your appointment if it was scheduled that far in advance.7Centers for Medicare & Medicaid Services. Standard Notice and Consent Documents Under the No Surprises Act You are never required to sign. For emergency services the consent exception does not apply at all. A consent form shoved at you in an emergency department is not valid.
When Two Plans Cover You
If you’re covered under two health plans at once, say your own employer plan and your spouse’s, coordination of benefits decides which pays first. The primary plan processes the claim and pays up to its coverage limits. The secondary plan picks up some or all of what remains, depending on its own terms.8Medicare.gov. How Medicare Works With Other Insurance
The order follows a standard hierarchy. A plan that covers you as an employee usually takes priority over one that covers you as a dependent. For children covered under both parents’ plans, the “birthday rule” generally makes the plan of the parent whose birthday falls earlier in the calendar year primary. Whatever neither plan pays is yours.
Errors here are common. Claims submitted to the wrong plan first produce denials, delays, and confusing bills. Whenever your coverage changes, update coordination of benefits information with both insurers.
Appealing a Denied Claim
When a payer denies a claim or covers less than you expected, you can challenge the decision. Start with the EOB. The reason codes on it tell you exactly what your appeal needs to address.
Federal law requires most health plans to offer two levels of review. First is an internal appeal, where the payer’s own reviewers reconsider the decision. For urgent medical situations the payer must respond within 72 hours.9eCFR. 45 CFR 147.136 – Internal Claims and Appeals and External Review Processes Standard non-urgent appeals typically require a response within 30 to 60 days, depending on whether the claim involves care you haven’t yet received or care already provided.
If the internal appeal upholds the denial, you can request an external review. Your case goes to an independent review organization with no financial ties to your insurer. The reviewer evaluates the clinical evidence and coverage terms, and the decision is binding on the plan. External review is especially useful for denials based on medical necessity, where an independent physician’s judgment can override the insurer’s. Instructions for requesting external review are generally included in the denial letter, so read it carefully.
Spotting Billing Fraud on Your Own Account
Because the payer isn’t in the room when care is delivered, some providers misrepresent what happened. Two common schemes are upcoding, where a provider bills for a more expensive procedure than was actually performed, and unbundling, where services normally billed as a single package are broken into separate charges to inflate the total.
The simplest way to catch this on claims filed under your name is to compare each EOB against the care you actually received. Procedures you don’t recognize, dates of service when you weren’t seen, and duplicate charges for the same visit are all worth reporting to your insurer. Fraudulent claims against federal health programs can also expose the provider to civil penalties and treble damages under the False Claims Act.10Office of the Law Revision Counsel. 31 USC 3729 – False Claims