The defining characteristic of a Long-Term Care Hospital, from Medicare’s perspective, is not its physical facility or its patient population alone — it is the statutory requirement that the hospital maintain an average Medicare inpatient length of stay greater than 25 days. This single facility-level metric determines whether a hospital qualifies for LTCH status at all, and a facility that falls short of the 25-day threshold risks losing its LTCH payment classification entirely, with consequences that extend to every claim billed during the affected period. For LTCH administrators and compliance teams, monitoring, documenting, and defending this average length of stay calculation is a foundational denial prevention function, not a peripheral cost reporting detail.
This article explains what the 25-day average length of stay requirement is and why it exists, how the calculation works and what CMS and its contractors examine when verifying compliance, the documentation and operational practices that help LTCHs maintain and defend their status, and how facilities should respond when the calculation is challenged. It closes with how HealthBridge US supports LTCHs protecting their Medicare classification and preventing related claim denials.
What the 25-Day Requirement Is and Why It Exists
By statute, a Long-Term Care Hospital is defined as a hospital with an average Medicare inpatient length of stay, as determined by the Secretary of Health and Human Services, of greater than 25 days. This requirement was established in 1983 specifically to distinguish LTCHs from general acute care hospitals, reflecting the reality that LTCHs are designed to care for medically complex patients — including those with traumatic brain injury, conditions requiring prolonged mechanical ventilation, paralysis, significant wound care needs, or multi-organ failure — whose clinical needs require a proportionally longer stay than the typical acute care admission.
To qualify for LTCH status, a facility must also independently meet Medicare’s conditions of participation applicable to acute care hospitals, obtain the appropriate state licensure for its location, and structurally qualify under the statutory framework governing LTCHs, which by law does not permit LTCH units within a general acute care hospital in the way IPPS hospitals can maintain excluded units — LTCH status instead applies to freestanding facilities, satellite facilities, or hospitals-within-hospitals that are co-located with, but organizationally and physically distinct from, an acute care hospital or other Medicare provider.
How the Average Length of Stay Calculation Works
The 25-day average length of stay calculation is based on the facility’s Medicare inpatient population over a defined measurement period, generally the hospital’s cost reporting period, and is calculated by CMS and its contractors using Medicare claims data reflecting the facility’s actual billed length of stay for each Medicare inpatient discharge during that period. Because this is an average across the facility’s entire Medicare inpatient population, individual short stays do not automatically disqualify a facility, but a pattern of shorter-than-expected stays across a meaningful share of the hospital’s Medicare discharges can pull the facility’s average below the required threshold even if many other stays comfortably exceed 25 days.
This average-based structure creates a specific compliance dynamic: a facility experiencing a general trend toward shorter stays — whether due to changes in referral patterns, clinical practice improvements that appropriately shorten recovery time, or a shift in payer mix that increases the proportion of shorter-stay admissions — needs to monitor its rolling average length of stay proactively throughout the cost reporting period, rather than discovering a compliance problem only when CMS calculates the facility’s final average at the end of the period.
Why This Rule Creates Sustained Denial Risk
Because LTCH status is a threshold, facility-level determination rather than a claim-specific coverage question, a facility that fails to maintain the required average length of stay faces consequences that extend well beyond any single claim. Medicare Administrative Contractors (MACs) and CMS’s broader program integrity apparatus monitor LTCH average length of stay data on an ongoing basis, and a facility whose calculated average falls at or below the 25-day threshold risks reclassification, which can result in retrospective payment adjustments across the affected cost reporting period rather than a denial limited to the specific short-stay claims that contributed to the shortfall.
This creates a denial prevention dynamic that is fundamentally different from the claim-level documentation issues that dominate acute care hospital audits. An LTCH cannot simply defend a specific claim with better clinical documentation if the underlying issue is a facility-wide average length of stay that falls short of the statutory threshold; the remedy has to address the facility’s overall admission and discharge patterns, not the documentation quality of any individual chart.
Monitoring and Documentation Practices That Support Compliance
LTCHs that successfully maintain compliance with the 25-day requirement generally build a rolling, real-time tracking process that calculates the facility’s Medicare average length of stay on a regular basis throughout the cost reporting period — monthly or even more frequently — rather than waiting for a year-end calculation to reveal a compliance problem that can no longer be addressed within that period. This rolling calculation should be reconciled against the same claims-based methodology CMS and its contractors use, so that the facility’s internal tracking reflects an accurate, audit-consistent picture of its current standing relative to the threshold.
Admission criteria and case selection practices also play a direct role in denial prevention here. LTCHs should maintain clear, consistent documentation of the clinical criteria used to determine appropriateness for LTCH-level admission, ensuring that patients accepted for LTCH care genuinely require the extended, medically complex treatment course the LTCH model is designed to provide, rather than admissions that are more appropriately suited to a shorter post-acute stay in another setting. This is not simply a compliance exercise — a facility whose admission practices consistently align with genuine LTCH-level clinical need is far less likely to experience the gradual drift toward shorter average stays that can jeopardize its overall length of stay compliance.
Cross-Departmental Ownership of Length of Stay Compliance
Because average length of stay compliance depends on data generated across admissions, case management, clinical care, and billing, no single department can own this compliance function in isolation. Admission coordinators and referral staff influence the calculation from the outset by determining which patients are accepted for LTCH-level care in the first place; case managers and physicians influence it throughout the stay by managing the pace and appropriateness of the patient’s clinical progress and eventual discharge timing; and HIM and billing staff influence the accuracy of the underlying claims data CMS uses to calculate the facility’s average. LTCHs that establish a standing, cross-departmental length of stay compliance committee — reviewing the rolling calculation, recent admission patterns, and any emerging case mix shifts on a regular basis — are better positioned to catch a developing compliance concern early, while there is still time within the cost reporting period to address it through appropriate clinical and operational means, rather than discovering the issue only after the period has closed and the facility’s classification is already at risk.
Responding When the Calculation Is Challenged
If CMS or a MAC identifies a potential average length of stay compliance concern, the LTCH’s response should include its own internal tracking data and methodology, allowing for a direct reconciliation against CMS’s calculation to identify any discrepancy in the underlying claims data or measurement period used. Where the facility’s own data confirms a genuine shortfall, the response should also address the facility’s corrective action — changes to admission criteria, case management practices, or discharge planning timing — being implemented to restore compliance going forward, since demonstrating a credible path back to compliance is relevant to how CMS and its contractors evaluate the situation.
Facilities disputing a specific reclassification determination retain applicable administrative appeal rights, though the procedural pathway for a facility-level classification dispute differs from the standard Medicare claims appeals process used for individual claim denials, and LTCHs should confirm the applicable appeal forum and deadlines early, given how much is at stake in a reclassification determination.
Building Proactive Length of Stay Compliance
The most effective defense against 25-day average length of stay compliance risk is continuous, data-driven monitoring integrated directly into the LTCH’s case management and utilization review functions, rather than a periodic compliance check disconnected from day-to-day admission and discharge decisions. Case managers and admission coordinators should have visibility into the facility’s current rolling average, allowing admission decisions to be made with an informed understanding of how the facility’s overall length of stay profile is trending. Regular reporting to hospital leadership on the facility’s rolling average, alongside the underlying case mix and referral pattern data driving that average, allows administrative and clinical leadership to identify and address emerging trends well before they threaten the facility’s fundamental Medicare classification.
The Interaction Between Length of Stay Compliance and Site-Neutral Payment
LTCHs should also understand that the 25-day average length of stay requirement, while foundational to the facility’s overall classification, operates alongside the claim-specific site-neutral payment policy that separately determines how individual discharges are reimbursed. A facility can maintain a compliant average length of stay while still having a substantial share of its discharges paid at the lower, site-neutral rate if those individual cases do not meet the specific clinical criteria — such as a qualifying intensive care unit stay or extended mechanical ventilation — required for standard LTCH PPS payment. Because site-neutral cases, by definition, tend to involve shorter and less resource-intensive stays than the facility’s standard LTCH-level cases, a rising proportion of site-neutral discharges can itself be an early warning sign that the facility’s overall case mix is shifting in a direction that could eventually pressure its average length of stay compliance as well. LTCHs benefit from tracking both metrics together — the proportion of discharges paid at the site-neutral rate and the facility’s rolling average length of stay — since a sustained shift in one is often an early signal of pressure building on the other.
How HealthBridge US Supports Your Long-Term Care Hospital
The 25-day average length of stay requirement is a facility-defining compliance metric with consequences that reach far beyond any individual claim, making proactive, continuous monitoring essential rather than optional for LTCH administrators. HealthBridge US supports Long-Term Care Hospitals with average length of stay tracking and reconciliation against CMS methodology, admission criteria and case management practice review, compliance risk assessment, and response support when a facility’s length of stay compliance is challenged. If your LTCH wants to strengthen length of stay monitoring or needs support responding to a compliance concern, HealthBridge US is here to help — contact our team to discuss your Medicare claim denial prevention needs.
References
• Centers for Medicare & Medicaid Services. “Long-Term Care Hospital PPS.” https://www.cms.gov/medicare/payment/prospective-payment-systems/long-term-care-hospital
• Centers for Medicare & Medicaid Services. “Elements of LTCH PPS.” https://www.cms.gov/medicare/payment/prospective-payment-systems/long-term-care-hospital/elements
• Centers for Medicare & Medicaid Services. “Additional Documentation Request.” https://www.cms.gov/data-research/monitoring-programs/medicare-fee-service-compliance-programs/medical-review-education/additional-documentation-request
• Centers for Medicare & Medicaid Services. Medicare Claims Processing Manual, Chapter 29 (Appeals). https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c29.pdf
• Electronic Code of Federal Regulations. 42 CFR § 412.23 (Excluded Hospitals: Classifications). https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-B/part-412
• Centers for Medicare & Medicaid Services. “Medicare Fee for Service Recovery Audit Program.” https://www.cms.gov/data-research/monitoring-programs/medicare-fee-service-compliance-programs/medicare-fee-service-recovery-audit-program
HealthBridge US is here to help. Our compliance specialists support Long-Term Care Hospitals with average length of stay monitoring and Medicare claim denial prevention — contact us to protect your facility’s LTCH classification and reimbursement.
