2.1 How IPPS Works and How CMS Updates It

2.1 How IPPS Works and How CMS Updates It

Quick Answer: The Inpatient Prospective Payment System (IPPS) is how the Centers for Medicare & Medicaid Services (CMS) pays most acute-care hospitals a predetermined amount per inpatient discharge, not a bill of itemized charges. CMS updates IPPS each federal fiscal year through the combined IPPS / Long-Term Care Hospital Prospective Payment System (LTCH PPS) proposed and final rules. For discharges April 1 through September 30, 2026, FY 2026 IPPS uses ICD-10 MS-DRG GROUPER Version 43.1. Do not guess FY 2027 relative weights for current cases.

This independent OpenExamPrep section helps inpatient Certified Clinical Documentation Specialist (CCDS) candidates study CMS IPPS structure for Domain I. It is not an Association of Clinical Documentation Integrity Specialists (ACDIS) or CMS publication, and it does not claim official review or partnership with either organization.

Why Domain I starts with the payment system

ACDIS's CCDS exam places IPPS, reimbursement, and documentation in Domain I (15 of 120 scored items, 12.5%). You cannot interpret a working diagnosis-related group, a complication or comorbidity opportunity, or a query's payment effect unless you know that Medicare is buying a case, not a list of tests. The hospital's Medicare inpatient payment is largely decided when the Medicare Severity Diagnosis Related Group (MS-DRG) is assigned, using diagnosis and procedure codes built from the record.

Hospital outpatient facility payment uses a different system—the Outpatient Prospective Payment System (OPPS) and Ambulatory Payment Classifications (APCs). That outpatient machinery belongs to CCDS-O study, not this inpatient exam.

What prospective payment actually means

Under a retrospective cost system, a hospital billed charges or costs and waited for settlement. IPPS, used for most short-term acute-care hospitals since the 1980s, sets a federal standardized (base) operating amount in advance, then multiplies and adjusts it. Subject to add-on payments discussed below, the hospital receives one operating MS-DRG payment per stay, plus a parallel capital IPPS payment that uses the same MS-DRG relative weights.

IPPS covers most Medicare fee-for-service acute-care inpatient discharges. It does not pay critical access hospitals (CAHs), which use a reasonable-cost methodology, or several excluded hospital types that have their own prospective systems (for example LTCH PPS, inpatient psychiatric, and inpatient rehabilitation). CCDS items about grouping and documentation assume a typical IPPS acute-care hospital unless the stem says otherwise.

The conceptual payment stack

Think in layers, not in a memorized Table 5 number:

1. MS-DRG assignment — one grouper result for the stay (section 2.2).
2. Relative weight (RW) — a resource index for that MS-DRG compared with the average Medicare case. CMS uses the same weights for operating and capital rates.
3. Standardized amounts — national operating and capital base rates, updated annually. For FY 2026, CMS's final-rule fact sheet (CMS-1833-F) states a 2.6% increase in IPPS operating payment rates for hospitals that successfully participate in the Hospital Inpatient Quality Reporting (IQR) program and are meaningful electronic health record (EHR) users under the Medicare Promoting Interoperability Program. That figure reflects a 3.3% market-basket increase minus a 0.7 percentage-point productivity adjustment. CMS also rebased the IPPS market baskets to a 2023 base year and set a national labor-related share of 66%.
4. Wage index — adjusts the labor portion of the operating (and capital) rate for local hospital labor markets.
5. Hospital-level add-ons — when statutory criteria are met, examples include indirect medical education (IME) and disproportionate share hospital (DSH) / uncompensated-care payments.
6. Case-level add-ons — new technology add-on payments (NTAPs) for CMS-approved technologies, and outlier payments when costs are extraordinarily high relative to the MS-DRG payment (conceptual treatment in section 2.2).
7. Quality program withholds and redistributions — Hospital Value-Based Purchasing (VBP) funds a pool by reducing base operating DRG payments (CMS describes a 2% reduction redistributed as incentive payments). Domain VIII covers quality programs in depth; Domain I only needs you to know they modify the IPPS check and do not replace MS-DRG grouping.

Hospitals that fail IQR or Promoting Interoperability requirements take a reduced annual update. You do not need to compute the penalty on the exam; you need to know the update is conditional.

CMS's Medicare Learning Network payment-systems materials also describe a 10% cap on year-to-year decreases in an individual MS-DRG relative weight, so a single GROUPER revision does not collapse payment for that group overnight. Recalibration of weights is designed to be budget-neutral across the IPPS as a whole: weights shifting among MS-DRGs is not a national giveaway. It is still a this-hospital, this-case payment change when documentation moves a stay from one MS-DRG to another.

How CMS updates IPPS each year

Federal fiscal year YYYY runs October 1 of YYYY−1 through September 30 of YYYY. FY 2026 is therefore October 1, 2025 through September 30, 2026. This section's lastUpdated date (2026-09-19) is still inside FY 2026.

CMS finalized Version 43.0 for discharges beginning October 1, 2025, then released Version 43.1 for discharges from April 1 through September 30, 2026. CMS has since issued the FY 2027 IPPS/LTCH PPS final rule to take effect October 1, 2026. This study resource does not ask you to memorize FY 2027 Table 5 relative weights. If an item needs a weight, the stem should supply it, or the question is testing the concept of a weight, not a number you guessed from a slide deck.

Tables you will hear about in CDI operations:

• Table 5 — MS-DRG titles, relative weights, geometric and arithmetic mean length of stay.
• Diagnosis and procedure lists in annual rulemaking (often Tables 6A–6K) — new, revised, and deleted codes; CC and MCC lists; CC exclusion list (Table 6K conceptually). Chapter 3.1 teaches exclusion logic.
• Wage-index and standardized-amount tables.

ACDIS allows optional use of DRG Expert (any year) as a CCDS test-day resource. That commercial compilation is a lookup aid. It is not a substitute for knowing how CMS updates the payment system, and it does not freeze last year's weights onto this year's discharges.

A September 2026 working example

Riverbend Memorial, an IPPS hospital, admits Mr. Hale on September 18, 2026 for community-acquired pneumonia. The CDI specialist runs a working MS-DRG in Version 43.1. On September 22 the attending documents acute hypoxic respiratory failure, which may move the case within the respiratory medical family depending on CC/MCC logic (Chapter 3). Discharge occurs September 25, 2026. FY 2026 rules still govern that claim.

If the same patient were discharged October 2, 2026, the hospital would group with the FY 2027 GROUPER and Table 5. The clinical story did not change at midnight on October 1; the payment software and weights did. Programs that keep last year's grouper running into October create false case-mix swings that are really version problems.

Traps that show up as Domain I recall items

• Charges are not the MS-DRG. Itemized CT scans do not add line-item Medicare payment under IPPS.
• Relative weights are not dollars. A weight of 2.0 means roughly twice the resource index of 1.0 before wage index and add-ons—not two dollars.
• Do not apply next year's weights to this year's discharges. FY 2026 remains in effect through 2026-09-30.
• OPPS is not a lighter IPPS. It is a different classification for a different setting.
• The final rule is not optional commentary. After October 1, the finalized GROUPER and rates are the payment system.

Walk into Domain I able to say: IPPS is CMS's per-discharge prospective payment for most acute-care inpatient stays; CMS updates it annually through IPPS/LTCH PPS rulemaking effective each October 1; FY 2026 discharges from April 1 through September 30, 2026 use GROUPER Version 43.1; and documentation matters because it determines the codes that determine the MS-DRG.