Ambulatory surgery center (ASC) billing has its own rules. The facility bills separately from the surgeon, Medicare pays only for procedures on its covered list, and implants, supplies and discontinued cases each follow specific payment rules. A billing service that mostly works for physician offices can miss these details.
This guide is for ASC administrators, business office managers and owners deciding whether to hire an outside ASC billing service, or checking whether their current one is doing the job. It covers the ASC-specific rules a service has to handle, what the service should do, and how to evaluate one. For a step-by-step view of the billing workflow itself, see how ASC billing services work and ASC billing and coding.
What makes ASC billing different from physician billing?
An ASC bills for the facility's part of a surgical case, while the surgeon and anesthesia provider bill separately for their professional services. Medicare pays the facility under its own ASC payment system, with its own list of covered procedures and rules for what is packaged into the facility payment.
That split means one surgery creates at least two claims, often more. The facility claim and the professional claims have to describe the same case consistently, even though they are prepared by different teams and may go out on different claim forms depending on the payer.
| Claim | Who bills | What it covers |
|---|---|---|
| Facility claim | The ASC | Facility services tied to the covered procedure, such as nursing, the operating room, supplies and equipment |
| Surgeon's professional claim | The surgeon or the surgeon's practice | The surgeon's professional service |
| Anesthesia claim | The anesthesia provider or group | The anesthesia professional service |
How does Medicare pay ASCs?
Medicare pays ASCs a set amount for each covered surgical procedure, adjusted for local wage levels. The Centers for Medicare & Medicaid Services (CMS) publishes the procedure codes that may be performed in an ASC and the payment rates, and updates them through annual policy files and rate addenda.
Under the federal rules in 42 CFR (Code of Federal Regulations) Part 416, Subpart F, several points matter for billing:
- Covered procedures. Medicare pays the facility only for procedures it treats as covered surgical procedures. The requirements for that list changed for services on or after January 1, 2026, so check the current rules and files for the date of service.
- Packaged items. Many items are included in the facility payment and not billed separately, including nursing services, use of the facility, most medical and surgical supplies, equipment, and implanted prosthetic devices that are not on pass-through status.
- Separately payable ancillary services. Some items integral to the procedure can be paid separately, such as brachytherapy sources and certain implantable items with pass-through status.
- Multiple procedures. When more than one covered procedure is done in the same session, Medicare generally pays 100 percent for the procedure with the highest rate and 50 percent for the others, with exceptions.
- Discontinued procedures. If a case is stopped after the patient is taken to the room but before anesthesia is induced, payment is generally half. If it is stopped after induction or after the procedure starts, payment is generally full. For device-intensive procedures, the device portion is removed first in certain cases.
- Device credits. When an implanted device is replaced at no cost, or the ASC receives full or qualifying partial credit for it, Medicare reduces the payment for procedures where the device is a significant part of the cost.
Commercial payers and Medicare Advantage plans have their own contracts, covered-service lists and rules. A good billing service knows which rules apply to which payer and does not apply the Medicare framework to everyone.
Where do ASC claims usually go wrong?
ASC claims usually go wrong when the facility claim does not match the operative note, when implants and supplies are billed or omitted incorrectly, or when modifiers are missing or misused. Each of these comes back to documentation.
- Coding from the schedule instead of the operative note. What was booked is not always what was performed.
- Implant and supply errors. Billing items that are packaged, or missing items that are separately payable or carved out in a commercial contract.
- Modifiers. Missing or incorrect modifiers for discontinued procedures, laterality, or distinct procedures during the same session.
- Authorization and eligibility gaps. A procedure performed without the required prior authorization can be denied regardless of how well it is coded.
- Mismatched claims. Facility and professional claims that describe the case differently.
Complete charting makes all of this easier. See our guide to ASC documentation requirements.
What should an outsourced ASC billing service do?
An outsourced ASC billing service should handle coding from the operative record, facility claim preparation and submission, payment posting, denial follow-up and appeals, and reporting. It should also understand each payer contract well enough to catch underpayments.
- Verify eligibility and track authorizations before the date of surgery.
- Code the facility claim from the operative note and implant records, not the booking.
- Apply payer-specific rules for packaged and separately payable items.
- Submit claims and track their status through the clearinghouse.
- Post payments and compare them with the contracted amount.
- Work denials and underpayments, with appeals where justified.
- Report results by payer, procedure and surgeon.
