CMS updated its Two-Midnight Rule Fact Sheet on March 12, 2026, reiterating that Medicare Advantage plans must follow the rule for admission decisions but retaining the right to audit inpatient claims under their own clinical criteria. CMS also announced that the inpatient-only (IPO) list will be phased out over three years starting in 2026. For admitting physicians and hospitalists, the practical effect is a higher rate of MA payer downgrades from inpatient to observation, a longer audit tail, and more revenue at risk if documentation does not establish medical necessity in real time.
What the rule actually requires
The two-midnight rule presumes that hospitalizations expected to span two midnights are appropriate for inpatient admission, and hospitalizations expected to span less than two midnights are appropriate for observation, with documented exceptions for case-by-case medical necessity and the inpatient-only list. The rule applies to both traditional Medicare Part A and, since 2024, to Medicare Advantage plans. The MA wrinkle is that the presumption is not as protective for MA claims as it is for traditional Medicare; MA plans can still apply their published clinical criteria and downgrade inpatient claims to observation if criteria are not met.
Where MA payers downgrade most often
MA downgrades cluster in predictable scenarios. Chest pain admissions where troponins are negative and the patient is observed for less than two midnights routinely move to observation. Syncope workups, low-risk cellulitis, and asymptomatic hypertension fall into the same pattern. Surgical recoveries that were historically inpatient under the IPO list are increasingly billed as outpatient procedures with overnight observation. Behavioral health admissions for short-stay stabilization are heavily downgraded. Knowing the patterns lets admitting physicians document expected length of stay and clinical reasoning at the time of admission, which is the highest-value defense against later downgrade.
The expected length of stay note
The single most important documentation element is a note at admission that states the expected length of stay and the clinical reasoning. Words matter here: “I expect this patient will require inpatient care spanning at least two midnights based on [specific clinical findings]” carries more weight in audit than “admit to medicine, will follow.” MA payers routinely audit admissions for the expected length of stay note, and its absence is the most common reason for downgrade. The note takes 30 seconds to write at the time of admission and is virtually impossible to reconstruct credibly after the fact.
Inpatient-only list phase-out
The IPO list previously protected certain procedures from downgrade by guaranteeing inpatient status. Starting in 2026, CMS will phase out the list over three years, moving procedures to a new outpatient-with-observation framework. Total joint replacement, certain spinal procedures, and selected cardiac interventions are early candidates. Surgeons and admitting practices should track the phase-out schedule for the procedures they perform most often, because the day a procedure leaves the IPO list is the day downgrade risk begins. Some procedures will move to a hybrid status where the surgeon must specifically document why this case requires inpatient over outpatient.
Appealing MA downgrades
MA downgrades are appealable, and the appeal process has different timelines than traditional Medicare. The first-level appeal is internal to the plan and typically has a 60-day window from the original determination. The second-level appeal goes to an independent review entity. The third-level goes to an administrative law judge. Appeals win at meaningfully higher rates when the original chart contains an expected length of stay note, real-time clinical decision-making, and reference to specific Milliman or InterQual criteria where applicable. Appeals lose when the documentation reads like a retrospective justification.
The plan’s published clinical criteria
CMS now requires MA plans to make their clinical criteria for medical necessity decisions available in a publicly accessible way. That is a tool admitting practices have not historically used. Pulling the plan’s specific Milliman or InterQual reference for a contested admission, and citing it in real-time documentation, gives the admitting physician’s note alignment with the criteria the plan will use to audit. Practices that pull this content into a working reference (organized by the plans they admit to most often) raise their inpatient retention rates without changing clinical decisions.
How MHB helps admitting practices
For hospitalist groups, surgical practices, and admitting physicians who want their inpatient versus observation decisions reviewed for documentation strength before submission, our team supports specialty medical coding for inpatient and observation billing, with MA payer-specific criteria mapping and downgrade appeal support. The work runs in the practice’s existing systems.
The bottom line
The two-midnight rule applies to MA plans, but the protection is less complete than it is for traditional Medicare. Documentation written at the time of admission, with expected length of stay and clinical reasoning, is the difference between an inpatient claim that holds and one that downgrades 90 days later. The IPO phase-out adds a new dimension. Both changes reward practices that document defensively in real time.
