The mortality and readmission rates published on Medicare's hospital comparison tools have carried a limitation most patients never knew about. For years, they have been calculated largely from fee-for-service claims, which now describe less than half of the Medicare population.
That is changing. In the inpatient payment rule finalized on July 31, the Centers for Medicare & Medicaid Services finalized modifications to eight claims-based measures that add Medicare Advantage patients to the calculations and shorten the performance period used to produce them.
For anyone who has looked up a hospital before a scheduled surgery or while choosing where a parent should be treated, this is a change to what the number on the screen actually represents.
The Measurement Gap CMS Is Closing
Medicare Advantage plans are private insurance products that replace traditional Medicare coverage. Enrollment has grown steadily for two decades, and it now covers more than half of all Medicare beneficiaries.
Claims-based quality measures, though, were built on traditional fee-for-service claims, because those flow directly to CMS in a standardized form as a byproduct of payment. Advantage plans pay hospitals themselves and submit encounter data separately, which historically has not been integrated into these measures.
The result was a scorecard describing a shrinking slice of a hospital's Medicare patients. A hospital in a market where Advantage penetration runs high could have most of its Medicare volume excluded from its own publicly reported mortality and readmission figures.
According to the CMS fact sheet, the agency said "these modifications will better reflect overall patient care coordination among a broader population" of patients, improving measure reliability. The full rule is available as Federal Register document 2026-15833.
Half the Program Was Missing from the Scorecard
The specific measures being modified fall into two groups, both beginning with the FY 2028 payment determination.
Three Excess Days in Acute Care measures are affected, covering acute myocardial infarction, heart failure, and pneumonia. These track how many days after discharge a patient spends in emergency department visits, observation stays or readmissions, which captures more of the post-discharge picture than a simple readmission count.
Five 30-day mortality measures are also modified, covering heart attack, heart failure, pneumonia, chronic obstructive pulmonary disease and coronary artery bypass graft surgery. CMS is adopting the modified versions in the Hospital Inpatient Quality Reporting Program first, then moving them into the Hospital Value-Based Purchasing Program, where the changes take effect with the FY 2032 program year.
Separately, the agency adopted a new Excess Days in Acute Care measure for diabetes beginning with the FY 2029 payment determination.
Whether adding Advantage patients raises or lowers any individual hospital's reported rates is not something CMS projected, and the direction is not obvious. It depends on how the two populations differ at each hospital in ways the risk adjustment may or may not capture.
A Shorter Look-Back Window
The second change is easier to overlook and arguably more useful to patients.
CMS is shortening the performance period for these measures from three years to two. That reduces how far into the past a published rate reaches.
A three-year window smooths out random variation, which is the statistical argument for it. It also means a hospital that changed leadership, rebuilt a cardiac program or fixed a staffing problem two years ago is still being described partly by the version of itself that existed before. For a family comparing hospitals, older data describes an institution that may no longer exist in the same form.
CMS framed the shortening as allowing results to reflect more recent hospital performance and provide more actionable insight for quality improvement. The tradeoff is a smaller sample, which can make small-volume hospitals harder to distinguish from one another with confidence.
Comparison Data Will Not Change Overnight
The practical timeline is longer than the announcement suggests.
The modifications begin with the FY 2028 payment determination, which means the publicly displayed figures on Medicare's comparison tools will continue reflecting the current methodology for some time. Anyone comparing hospitals this month is looking at measures built largely on fee-for-service claims over a three-year window.
That is not a reason to ignore the data. It is a reason to read it with its limitations in mind, particularly in markets where Advantage enrollment is high, and to weigh it alongside things a rate cannot capture. Volume for a specific procedure, whether the hospital has the specialty service a patient actually needs, and distance from family who will visit all matter, and none appear in a mortality rate.
Risk-adjusted mortality and readmission figures are also comparisons against expected performance for a hospital's case mix, not raw counts. A hospital treating sicker patients is not penalized for that in principle, though how well any risk model accomplishes that is a longstanding technical debate.
Open Questions the Rule Does Not Answer
CMS has not published analysis showing how hospital scores shift once Advantage patients are included, and no such analysis can exist until the measures are calculated under the new methodology.
The completeness and consistency of Medicare Advantage encounter data compared with fee-for-service claims has been raised as a technical question in health services research generally. Whether it materially affects these specific measures is not something the rule addresses.
The confirmed facts are that Medicare finalized modifications adding Medicare Advantage patients to eight claims-based mortality and readmission measures and shortening the performance period from three years to two, beginning with the FY 2028 payment determination. The people most affected are patients and families comparing hospitals, particularly in markets with high Advantage enrollment. The most reasonable action is to keep using the published data while understanding what it currently covers. The central uncertainty is how individual hospital scores change once a fuller population is counted, which no available evidence answers.
Choosing where to receive care should involve the treating clinician, who knows which hospitals have the specific capability a given condition requires.
Frequently Asked Questions
What did CMS change?
It finalized modifications to eight claims-based hospital quality measures, adding Medicare Advantage patients and shortening the performance period from three years to two, beginning with the FY 2028 payment determination.
Which measures are affected?
Three Excess Days in Acute Care measures covering heart attack, heart failure and pneumonia, and five 30-day mortality measures covering heart attack, heart failure, pneumonia, COPD and coronary artery bypass graft surgery.
Why were Medicare Advantage patients excluded before?
Claims-based measures were built on fee-for-service claims, which flow to CMS directly as part of payment. Advantage plans pay hospitals themselves and submit encounter data separately.
How many Medicare beneficiaries are in Advantage plans?
More than half, according to CMS.
Will hospital ratings go up or down?
CMS has not projected the direction. It depends on how each hospital's Advantage and fee-for-service populations differ in ways risk adjustment may not fully capture.
When will the published numbers change?
Not immediately. The modifications begin with the FY 2028 payment determination, so currently displayed figures still reflect the existing methodology.
Should I still use hospital comparison data?
Yes, while understanding its limits. Pair it with procedure volume, whether the hospital offers the specific service needed, and guidance from the treating clinician.
