Key facts for DRG 999
- FY2027 relative weight
- n/a
- Change vs FY2026
- n/a
- FY2026 weight n/a
- Geometric mean LOS
- n/a days
- Arithmetic mean n/a days
- MDC
- None
- Not assigned to an MDC
- Severity level
- single severity level
- Transfer policy
- Not a transfer DRG
TL;DR
MS-DRG 999 is a medical group in MDC (Not assigned to an MDC) at a single-severity group of its family. CMS assigns it a FY2027 relative weight of n/a with a geometric mean length of stay of n/a days and an arithmetic mean of n/a. A prior-year weight is not available for comparison. CMS does not split this group by severity.
What changed from FY2026 to FY2027
CMS recalibrates every MS-DRG weight annually from the prior year's MedPAR claims. For DRG 999 the FY2027 relative weight is n/a against n/a in FY2026, a fall of 0.00%.
| Metric | FY2026 | FY2027 | Change |
|---|---|---|---|
| Relative weight | n/a | n/a | n/a |
| Geometric mean LOS (days) | n/a | n/a | n/a |
| Arithmetic mean LOS (days) | n/a | n/a | n/a |
CC and MCC family
DRG 999 stands alone: CMS does not split this base group by CC or MCC severity, so complication documentation does not move the assignment, although it still affects quality and risk-adjustment reporting.
Grouper logic (v44 Definitions Manual)
The Definitions Manual assigns DRG 999 through the MDC principal-diagnosis table and the absence of a qualifying operating-room procedure rather than a DRG-specific code list. See the manual chapter for MDC .
Documentation and denial exposure
As a medical DRG, assignment depends on the principal diagnosis sequenced from the attending's documentation; a secondary condition sequenced first, or a symptom code in place of the confirmed diagnosis, changes the MDC or the DRG. Because this family has no severity split, review risk concentrates on medical-necessity of the admission itself and on the two-midnight benchmark. Typical inpatient denial codes for this group: CARC 16 (claim lacks information needed to group the stay), CARC 50 (the admission or procedure is judged not medically necessary), CARC 97 (a service is bundled into the DRG payment).
How QuickIntell uses DRG 999 data
QuickCode groups inpatient encounters against the current v44 logic, flags CC and MCC candidates that lack supporting documentation, and shows the weight difference across the family before the claim drops. QuickScribe captures the attending's language that supports severity, and QuickRCM works DRG-validation denials with the grouper evidence attached.
Frequently asked questions — DRG 999
What is MS-DRG 999?
MS-DRG 999 is "Ungroupable", a medical Medicare Severity Diagnosis-Related Group in MDC , Not assigned to an MDC. Medicare pays inpatient stays grouped here at the hospital's base rate multiplied by the DRG relative weight.
What is the FY2027 relative weight for DRG 999?
The FY2027 relative weight is n/a (IPPS final rule Table 5, effective October 1, 2026).
What is the average length of stay for DRG 999?
CMS reports a geometric mean length of stay of n/a days and an arithmetic mean of n/a days for FY2027. The geometric mean is used for transfer-payment calculations.
What documentation supports the severity level of DRG 999?
DRG 999 has no CC or MCC sibling, so secondary-diagnosis capture does not change the group or its weight. Review effort belongs instead on the principal diagnosis sequencing and the procedure codes that place the stay in this group, and on medical necessity of the inpatient admission itself under the two-midnight benchmark, which is where denials for single-severity groups concentrate.
Is DRG 999 a post-acute transfer DRG?
No. DRG 999 is not on the FY2027 post-acute care transfer list, so the transfer per-diem policy does not apply to it.
Sources
Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-02. Verify against the primary file before billing or contracting decisions.
- IPPS FY2027 Final Rule Table 5 (CMS-1849-F)Version v44 FY2027 · effective 2026-10-01 · file CMS-1849-F Table 5.txtSHA-256 01003dd571c1e2f5…
- IPPS FY2026 Final Rule Table 5 (CMS-1833-F)Version v43 FY2026 · effective 2025-10-01 · file CMS-1833-F Table 5.txtSHA-256 bf8c390d14b3cd3e…
- ICD-10 MS-DRG Definitions Manual v44 (text)Version v44 · effective 2026-10-01 · file fy2027-fr-icd10-ms-drg-definitions-manual-files-v44.zipSHA-256 ae4f6c11727fe91f…
Disclaimer
This page is an operational reference compiled from the CMS IPPS FY2027 final rule (Table 5) and the v44 ICD-10 MS-DRG Definitions Manual. Relative weights are national factors; actual payment depends on each hospital's wage-adjusted base rate, add-ons, outliers and transfer adjustments. Nothing here is legal, clinical or billing advice; verify grouping against your encoder and the published CMS files.