The same outpatient procedure can be billed two very different ways depending on whether it happens in an ASC or a hospital outpatient department. The facility, the payment system, the claim form and the patient’s share of the bill can all change.
The gap matters more in 2026, as CMS expands the list of procedures payable in ASCs and begins phasing out the inpatient-only list.
Here are 10 things to know:
1. Two different entities. An ASC is a separately certified facility for patients not expected to need hospitalization, with services generally anticipated to last no more than 24 hours after admission, per CMS. An HOPD is a department of a hospital and can sit on the main campus or off campus. A hospital can own an ASC, but ownership does not make it an HOPD; billing follows certification and enrollment, according to a MedIntelHub explainer published Oct. 18.
2. Two different payment systems. Medicare generally pays ASCs under the ASC payment system and HOPDs under the Hospital Outpatient Prospective Payment System. Most ASC rates start from OPPS relative weights, but the conversion factors differ. For 2026, the ASC conversion factor is $56.322 and the HOPD conversion factor is $91.415.
3. The payment gap has widened. ASC reimbursement fell from about 85% of HOPD rates to 62%, according to a KNG Health Consulting analysis prepared for the Ambulatory Surgery Center Association. The same analysis credited ASCs with $27.9 billion in Medicare savings from 2019 to 2024. H.R. 8091, the Outpatient Surgery Access Act of 2026, would align ASC annual updates with HOPDs starting in 2027.
4. A $1,698 difference on knee arthroscopy. Medicare’s Procedure Price Lookup lists a 2026 national average of $2,159 for knee arthroscopy (CPT 29881) in an ASC and $3,857 in an HOPD. The facility component accounts for the gap: $1,644 vs. $3,342. The listed patient share is $431 in an ASC and $771 in an HOPD, per MedIntelHub.
5. Patients do not always pay less in an ASC. For some high-cost orthopedic cases, the patient share runs higher in the ASC. For posterior lumbar interbody fusion (22630), Medicare lists a $4,473 patient share in an ASC vs. $2,038 in an HOPD, despite a lower total cost of $22,368 vs. $29,231. HOPD copayments for a single service are generally capped at the Part A inpatient deductible, $1,736 in 2026, while ASC patients generally owe 20% coinsurance after the $283 Part B deductible.
6. Different claim forms. A Medicare-certified ASC bills its facility claim as a supplier on the CMS-1500 or 837P. HOPDs bill on the CMS-1450 (UB-04) or 837I. That split means the two settings need separate registration, charge-capture and claim-edit workflows, according to MedIntelHub.
7. Different place-of-service codes. Professional claims for ASC services generally use POS 24. On-campus HOPDs use POS 22 and off-campus HOPDs use POS 19. Hospital modifiers PO and PN flag excepted and nonexcepted off-campus services and should not be appended to ASC claims. A physician office sharing an address with an ASC is still POS 11, according to MedIntelHub.
8. 560 codes added to the ASC covered procedures list. CMS’ 2026 final rule added 289 codes under revised eligibility criteria and 271 removed from the inpatient-only list, including electrophysiology ablations, percutaneous coronary intervention and lumbar fusion (22630, 22633). CMS also moved five general exclusion criteria into nonbinding physician considerations for patient safety. Qualifying ASCs and HOPDs received a 2.6% payment update.
9. IPO removal is not ASC approval. CMS began a three-year phaseout of the inpatient-only list in 2026, removing 285 mostly musculoskeletal procedures. Removal allows hospital outpatient payment when clinically appropriate but does not make a procedure ASC-payable on its own; ASCs must still check the covered procedures list for the date of service. CMS projects the 2026 rule will save Medicare and beneficiaries $11 billion over 10 years.
10. Site-neutral payment expands, narrowly. For 2026, CMS extended a Physician Fee Schedule-equivalent rate to designated drug-administration services at excepted off-campus provider-based departments. The change does not apply the office rate to HOPD surgical claims, according to MedIntelHub.
At the Becker’s 32nd Annual Meeting: The Business and Operations of ASCs, taking place October 29-31 in Chicago, ASC leaders, surgeons and healthcare executives will explore strategies to drive growth, enhance operational performance, navigate reimbursement challenges and prepare for the future of ambulatory surgery. Apply for complimentary registration now.
