Medicare’s Prospective Payment System controls hospital costs by paying a fixed, predetermined amount for each inpatient stay based on the patient’s diagnosis, rather than reimbursing whatever the hospital ends up spending. Congress built this into the Social Security Amendments of 1983 after open-ended cost reimbursement pushed the Medicare Hospital Insurance Trust Fund toward insolvency.1National Center for Biotechnology Information (NCBI). The First 3 Years of Medicare Prospective Payment: An Overview Once the price is set in advance, any spending above it comes out of the hospital’s pocket, and any savings below it stay with the hospital. That single change turned the financial logic of inpatient care upside down.
The Incentive Flip
Under the original 1966 Medicare payment model, hospitals sent in itemized bills and got paid based on their actual costs and charges. More services, longer stays, and more expensive equipment all produced larger Medicare payments.2NCBI. Medicare Payment Systems: A Look Back and a Look Forward Hospital spending outpaced general inflation for more than a decade, and no one in the system had a financial reason to spend less.
PPS took effect for hospital fiscal years beginning after September 30, 1983.3Social Security Administration. Social Security Amendments of 1983: Legislative History and Summary of Provisions Instead of paying for services rendered, Medicare pays a set price for a defined product: the hospital stay. The price is calculated before the patient is even admitted, based on what the diagnosis is expected to cost the average hospital to treat. Financial risk shifted from Medicare to the hospital overnight. Efficient care became profitable. Waste became a direct loss.
How the Fixed Price Gets Set
The engine behind inpatient PPS is the Diagnosis-Related Group. Section 1886(d) of the Social Security Act requires Health and Human Services to classify each stay into a DRG and assign it a payment weight reflecting the average resources hospitals use for patients in that group.4Office of the Law Revision Counsel. 42 U.S. Code 1395ww – Payments to Hospitals for Inpatient Hospital Services Medicare then multiplies a national base payment rate by that weight to arrive at what the hospital gets paid.5Centers for Medicare & Medicaid Services. Acute Inpatient PPS
The current version, Medicare Severity DRGs, sorts each discharge using the principal diagnosis, up to 24 additional diagnoses, and up to 25 procedures. For a limited set of MS-DRGs, age, sex, and discharge status also affect the assignment.6Centers for Medicare & Medicaid Services. MS-DRG Classifications and Software The point is to capture clinical complexity. A pneumonia patient who also has congestive heart failure will consume far more resources than one with pneumonia alone, and the DRG assignment reflects that.
Severity Tiers
Many base conditions split into multiple MS-DRGs based on complications and comorbidities. The system distinguishes cases with no complications, cases with complications or comorbidities that moderately affect resource use, and cases with major complications or comorbidities involving significant acute disease or chronic conditions in acute exacerbation.7PMC. Refinement of the Medicare Diagnosis-Related Groups to Incorporate a Measure of Severity A hip replacement without complications pays less than one where the patient develops a serious postoperative infection. Without these tiers, hospitals treating sicker patients would systematically lose money.
Local Wage Adjustment
Labor is the biggest slice of hospital spending, and wages vary sharply across the country. PPS applies a wage index to the labor-related portion of the payment. Each labor market area gets an index value equal to its average hospital hourly wage divided by the national average.8Centers for Medicare & Medicaid Services. Wage Index High-wage areas get multipliers above 1.0; low-wage areas fall below. Only the labor share of the payment moves with the index.
Guardrails Against Gaming
A pure fixed-payment rule creates two obvious problems: hospitals could refuse the most expensive patients, and they could shuffle patients between facilities to collect multiple full payments for one course of care. PPS blocks both.
Outlier Payments
When a case runs dramatically more expensive than typical for its DRG, Medicare adds an outlier payment on top of the standard amount. The hospital’s costs have to exceed the DRG payment plus a fixed-loss threshold before outliers kick in. For fiscal year 2026, that threshold is $40,397. CMS resets it each year to keep total outlier spending at a target share of overall payments.9Centers for Medicare & Medicaid Services. FY 2026 Hospital Inpatient Prospective Payment System (IPPS) and Long-Term Care Hospital Prospective Payment System Final Rule Without this safety valve, hospitals would have every reason to steer clear of the sickest patients.
Transfer Rules
If a hospital could admit a patient, provide one day of care, transfer the patient elsewhere, and still bank the full DRG payment, transfers would become a business strategy. Medicare pays a per-diem rate instead of the full DRG when a patient is transferred before completing the expected length of stay. The transferring hospital generally gets twice the per-diem for the first day and the standard per-diem for each additional day, capped at the full DRG amount.10MedPAC. Hospital Acute Inpatient Services Payment System A modified formula applies to certain DRGs with high first-day costs, paying half the full amount up front plus per-diems for subsequent days.
Annual Updates With a Built-In Efficiency Cut
PPS rates are not frozen. CMS updates them each year using a hospital market basket index that tracks what hospitals actually pay for labor, supplies, and equipment. The update carries its own cost-control feature: a productivity adjustment. For fiscal year 2026, the projected market basket increase is 3.3 percent, reduced by a 0.7 percentage point productivity adjustment, producing a 2.6 percent net increase in operating payment rates for qualifying hospitals.9Centers for Medicare & Medicaid Services. FY 2026 Hospital Inpatient Prospective Payment System (IPPS) and Long-Term Care Hospital Prospective Payment System Final Rule The productivity cut assumes hospitals should get more efficient over time, and it withholds part of the raise on that basis. A hospital that fails to improve loses ground in real terms every year.
Penalties That Stop Hospitals From Cutting Too Deep
Congress recognized early that a system rewarding lower spending would also reward cutting corners. Once PPS took effect, average lengths of stay dropped, discharges to nursing homes and home health agencies rose sharply, and reports surfaced of patients sent home in unstable condition or without adequate follow-up care.11U.S. Government Accountability Office. Quality of Care Issues in the Medicare Program Medicare has since layered quality-based payment adjustments on top of PPS to counter that pressure.
Value-Based Purchasing
The Hospital Value-Based Purchasing Program withholds a percentage of each hospital’s base DRG payments and redistributes the pool based on quality performance. Hospitals that score well can earn back more than what was withheld; those that score poorly get less.12Centers for Medicare & Medicaid Services. Hospital Value-Based Purchasing Program Scoring covers four domains: patient experience, clinical outcomes like mortality rates, safety measures such as hospital-acquired infections, and efficiency measured through Medicare spending per beneficiary.13eCFR. Incentive Payments Under the Hospital Value-Based Purchasing Program
Readmissions Reduction
The Hospital Readmissions Reduction Program cuts a hospital’s base DRG payments by up to 3 percent for the full fiscal year if its readmission rates are too high.14Centers for Medicare & Medicaid Services. Hospital Readmissions Reduction Program (HRRP) This targets the premature-discharge problem directly. A hospital that sends patients home too early to capture the DRG margin tends to see many of them return within 30 days, which triggers the penalty. Three percent applied to every Medicare payment across a full year adds up to serious money at a large facility.
The Same Logic in Other Care Settings
Fixed prospective payment now runs through nearly every Medicare care setting. Each system uses its own classification scheme, but the underlying rule is the same: pay a predetermined amount, and let the provider decide how to deliver care within that budget.
The Balanced Budget Act of 1997 moved skilled nursing facilities off cost-based reimbursement, effective for cost reporting periods beginning on or after July 1, 1998.15Centers for Medicare & Medicaid Services. Skilled Nursing Facility PPS Home health now runs on 30-day payment periods under the Patient-Driven Groupings Model, which classifies each period into a case-mix group using admission source, timing in the care sequence, clinical grouping, functional impairment, and comorbidities.16Centers for Medicare & Medicaid Services. Patient-Driven Groupings Model Overview Hospital outpatient departments use Ambulatory Payment Classifications that bundle a primary service with everything considered integral to it, mirroring how DRGs bundle inpatient care.17Centers for Medicare & Medicaid Services. OPPS – Payment Inpatient rehabilitation facilities operate under their own PPS with case-mix groups, a wage adjustment, and an outlier threshold calibrated to keep outlier payments at 3.0 percent of total IRF payments; facilities that fail quality reporting requirements lose 2 percentage points from their annual update.18Centers for Medicare & Medicaid Services. FY 2026 Inpatient Rehabilitation Facilities Prospective Payment System Final Rule
Did It Actually Work
Judged by what Congress set out to do, PPS slowed the growth of Medicare inpatient hospital spending. The rate of increase stayed above general inflation but pulled off the trajectory that had threatened the Trust Fund.1National Center for Biotechnology Information (NCBI). The First 3 Years of Medicare Prospective Payment: An Overview Hospitals shortened stays and found ways to deliver care using fewer resources per admission, which is exactly the behavior the system was engineered to produce.
The trade-offs came with it. Hospitals under financial pressure shifted costs to other payers, discharged patients into post-acute settings that were not always ready for them, and in some cases pared staffing in ways that affected care. The quality programs bolted on later exist because PPS by itself optimizes for cost, not outcomes. The current framework is best read as two forces pushing against each other: the fixed-price incentive that drives spending down, and the quality penalties that keep it from cutting too far, with CMS recalibrating the balance every year.