How Does an MS-DRG Determine Inpatient Payment?
An MS-DRG sets what Medicare pays for an inpatient stay. The diagnoses and procedures on the final bill put the stay in one group, and that group's relative weight times the hospital's base rate is the payment. This post prices one pneumonia stay three ways with FY 2027 numbers, so you can see how a single secondary diagnosis moves the payment by thousands of dollars.
Written by Salman Saeed, CEO and Co-Founder · Reviewed by a Certified Medical Coder · 
In short: the payment follows the group, not the charges and not the length of stay. One MCC, one CC or neither decides the severity tier, so the secondary diagnoses on the final bill matter as much as the principal one.
What Happens Between Discharge and the MS-DRG Payment?
Five things happen in order, and an error at any step changes the payment. The MS-DRG rule page explains the classification itself. This is the order a billing lead checks.
How Does One Secondary Diagnosis Change the DRG?
Some DRGs come in three severity tiers. For simple pneumonia, DRGs 193, 194 and 195 are the same group split by secondary diagnoses. The Version 44 logic checks for an MCC first: with an MCC the stay is DRG 193, with no MCC but a CC it is DRG 194, and with neither it is DRG 195.
Two CCs on one stay do not add up to an MCC and do not raise the payment past the CC tier. The CC and MCC lists are in Appendix C of the Definitions Manual. These examples use a stay with a principal diagnosis of J18.9, pneumonia, unspecified organism, and no operating room procedure.
| Secondary diagnosis on the stay | Appendix C level | DRG | Weight (FY 2027) |
|---|---|---|---|
| None | None | 195 | 0.6063 |
| N17.9 acute kidney failure, unspecified | CC | 194 | 0.7888 |
| E44.0 moderate protein-calorie malnutrition | CC | 194 | 0.7888 |
| J96.01 acute respiratory failure with hypoxia | MCC | 193 | 1.2825 |
| I50.23 acute on chronic systolic heart failure | MCC | 193 | 1.2825 |
| E43 unspecified severe protein-calorie malnutrition | MCC | 193 | 1.2825 |
| I50.9 heart failure, unspecified | Not on the CC or MCC list | 195 | 0.6063 |
What Does the Payment Look Like in Dollars?
Take the national FY 2027 standardized amounts from Table 1B of the final rule: $4,245.76 labor-related and $2,602.24 nonlabor-related, for a hospital that reports quality data and is a meaningful EHR user. Table 1B applies a 62 percent labor share, which is used when the wage index is 1.0 or lower.
The hospital has a wage index of 1.0000, no cost-of-living adjustment, and no teaching or disproportionate share add-ons. The wage index is invented. The standardized amounts and weights are from CMS tables. Operating payment only; capital, outliers and add-ons are paid separately.
That gap is why a documentation query on a single secondary diagnosis is worth a coder's time. The same gap runs the other way when a diagnosis is coded without clinical support, which is what a DRG validation review looks for.
Does Length of Stay Change an MS-DRG Payment?
Usually not. The payment is per discharge, and a short stay in a standard case pays the full DRG. The exception is a transfer. Table 5 marks DRGs 193, 194 and 195 as post-acute DRGs for FY 2027, so a discharge from one of them to a skilled nursing facility is a transfer under 42 CFR 412.4(c).
The same section treats a discharge to home health as a transfer when the home health services begin within 3 days. Under 412.4(f), a transferring hospital is paid a graduated per diem: the DRG payment divided by the geometric mean length of stay, paid at twice that amount for the first day and once for each later day, never more than the full DRG payment.
Table 5 gives DRG 195 a geometric mean length of stay of 2.2 days. Using the illustrative $4,151.94 payment from above:
The patient discharge status code on the bill is what tells the MAC whether the discharge is a transfer. A wrong status code produces a wrong payment in either direction.
How Do You Check a DRG Before the Final Bill Drops?
- Read the principal diagnosis against the UHDDS definition in the ICD-10-CM Official Guidelines: the condition established after study to be chiefly responsible for the admission. The circumstances of admission govern.
- Test each secondary diagnosis against the guideline definition of other diagnoses: it must need clinical evaluation, treatment, diagnostic procedures, a longer stay or more nursing care or monitoring.
- Query the provider on abnormal findings. The guidelines say they are not coded unless the provider indicates clinical significance, and that it is appropriate to ask.
- Confirm the discharge status code against where the patient actually went, because transfer DRGs pay on it.
- Confirm the admission order was valid. The two-midnight rule page covers when a stay counts as inpatient.
- Pull any outpatient services from the 3 calendar days before admission into the claim. The three-day payment window folds them into the inpatient payment.
- Group with the version that matches the discharge date. Version 44 starts October 1, 2026.
Physician services are not part of the DRG. The admitting physician bills initial hospital care, such as 99223, on a CMS-1500 separately.
Can a DRG Be Changed After the Claim Is Paid?
Yes. Under 42 CFR 476.71, a quality improvement organization checks the diagnostic and procedural information hospitals send through DRG validation, reviews a random sample of discharges each quarter, and sends corrected information to the Medicare administrative contractor when it finds the original was wrong.
If you disagree with a DRG change, a redetermination request must be filed within 120 calendar days of receiving the notice, under 42 CFR 405.942. Commercial payers pay according to the contract, so read it before you assume the same logic applies.
How Does Nucleus Align Handle Inpatient Claims?
Our hospital and facility billing covers UB-04 claim preparation, revenue-code validation, submission, payment reconciliation and denial management for inpatient, outpatient and emergency care. Our UB-04 accuracy checks include bill type, revenue codes, patient status, condition and occurrence codes, authorization requirements and payer-specific rules. See hospital and facility billing, or book a call. More explainers are on the blog.
- MS-DRG Classifications and Software · CMS
- FY 2027 IPPS final rule home page, Tables 1A to 1E and Table 5 · CMS
- FY 2027 IPPS final rule, 91 FR 49570 · Federal Register via govinfo
- ICD-10 MS-DRG Definitions Manual Version 44 · CMS
- 42 CFR 412.4, Discharges and transfers · eCFR
- 42 CFR 412.60, DRG classification and weighting factors · eCFR
- 42 CFR 476.71, QIO review responsibilities · eCFR
- 42 CFR 405.942, Time frame for filing a request for redetermination · eCFR
- ICD-10-CM Official Guidelines for Coding and Reporting FY 2027 · CMS
We check every rule, code and deadline against the official source. See our editorial policy.
Common Questions
Straight answers from the team that does the work.
Ask a billing lead directly. A 20-minute call, Monday to Friday, 9am to 5pm Eastern.
01How does an MS-DRG determine inpatient payment?
The grouper assigns each discharge to one MS-DRG using the principal diagnosis, secondary diagnoses, procedures and discharge status. Medicare then multiplies the DRG's relative weight by the hospital's base rate, adjusted for wage index and other factors. The payment is per discharge, not per day or per charge.
02Where do I find the relative weight for an MS-DRG?
Table 5 of the annual IPPS final rule lists every MS-DRG with its weight and its geometric and arithmetic mean length of stay. CMS posts it as a download on the final rule page for the fiscal year. For FY 2027, in the correction notice version of Table 5, DRG 195 is 0.6063, DRG 194 is 0.7888 and DRG 193 is 1.2825. The original final rule file showed 0.6062, 0.7886 and 1.2824.
03Does a second CC raise an MS-DRG payment?
No. In a three-tier family such as DRGs 193 to 195, the stay needs one MCC for the top tier or at least one CC for the middle tier. Extra CCs do not move it higher. Only an MCC that survives the principal diagnosis exclusion raises the tier.
04Do all payers pay by MS-DRG?
No. Medicare's IPPS uses MS-DRGs, but commercial and Medicaid payers pay according to their own contracts and rules. Read the contract to see which grouper, version and rate apply before you model expected payment, and do not reuse Medicare weights for those claims.
Talk to a Billing Lead.
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