Signature
PDC_stay = C_adj / (T - H)
| Inputs | Definition | Unit |
|---|---|---|
C_adj | Covered days on days outside stays, after supply overlapping a stay has been shifted to uncovered days after discharge | days |
T | Days in the treatment period before the adjustment, from the index date to the end date inclusive | days |
H | Inpatient and skilled nursing facility stay days within the period, including discharge dates | days, fewer than T |
PDC_stay | Proportion of days covered with inpatient and skilled nursing facility stay days removed | proportion, at most 1 |
|---|
Function
Proportion of days covered from pharmacy fill dates and days' supply function
Maps a patient's dispensing records, each a fill date and a days' supply, and an observation period to the proportion of days covered (PDC), the share of days in the period on which at least one fill provides medicine, each day counted once. Same-drug refills collected before the previous supply runs out are shifted to start the day after it ends, overlaps between different drugs in a class are not shifted, supply running past the end of the period is ignored, and the CMS method removes inpatient and skilled nursing facility stay days. The records follow the notation of the Proportion of Days Covered article. The medication possession ratio, which sums days' supply instead, is HE-FM-MPR-001.
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Implementations
Excel
Stay-adjusted PDC from named covered-day, period and stay cells
Excel divides the named cell holding the covered days outside stays by the period length less the stay days.
=CoveredDaysAdj/(PeriodDays-StayDays)
Assumptions
Facility supplies the medicine during an inpatient stay
The patient receives the medicine from the facility during the stay, so stay days are neither covered nor uncovered by pharmacy fills, and any supply accumulated during the stay can be used after returning home.
Stay supply shifted only to uncovered days after discharge
Supply that overlaps a stay moves only to days without coverage after discharge. When there are none, as in the second inpatient stay example of Attachment L (Example 2, Tables L-8 and L-9), the supply is not shifted and the covered stay days simply leave the numerator.
Worked examples
Ten-day inpatient stay inside the gap of the five-fill history
If the patient in the article's example was an inpatient on days 95 to 104, inside the gap, those 10 days leave the denominator. No supply overlapped the stay, so nothing is shifted, the numerator stays at 150 and the PDC rises from about 0.833 to 150 / 170, about 0.882.
C_adj = 150; T = 180; H = 10; PDC_stay = 0.8824
CMS example with supply shifted to the days after an inpatient stay
In the first inpatient stay example of Attachment L (Example 1, Tables L-6 and L-7), a 15-day period with coverage on days 1 to 8 and 12 to 15 and an inpatient stay on days 5 and 6 has a PDC of 12 out of 15, 80%. Removing the stay days and shifting their 2 days of supply to days 9 and 10 gives 12 covered days out of 13, 92%.
C_adj = 12; T = 15; H = 2; PDC_stay = 0.9231
CMS example where the stay adjustment lowers the PDC
In the second inpatient stay example of Attachment L (Example 2, Tables L-8 and L-9), coverage on days 1 to 7 and 12 to 15 with a stay on days 12 and 13 gives 11 out of 15 before adjustment, 73%. The covered stay days are removed and no uncovered days follow the stay to receive their supply, so the PDC becomes 9 out of 13, 69%.
C_adj = 9; T = 15; H = 2; PDC_stay = 0.6923
Common errors
Removing stay days from the PDC denominator only
In the second inpatient stay example of Attachment L (Example 2, Tables L-8 and L-9), keeping the 2 covered stay days in the numerator while removing them from the denominator gives 11 / 13, about 0.846, instead of 9 / 13, about 0.692 (computed here for illustration).
Removing stay days without shifting the supply that overlapped them
In the first inpatient stay example of Attachment L (Example 1, Tables L-6 and L-7), dropping days 5 and 6 without moving their supply to days 9 and 10 leaves 10 covered days of 13, about 0.769, instead of 12 of 13, about 0.923 (computed here for illustration).
Sources
CMS adjustment of the PDC for inpatient and skilled nursing facility stays
Centers for Medicare & Medicaid Services. Medicare 2026 Part C & D Star Ratings Technical Notes. Baltimore: CMS; updated 25 September 2025. Attachment L, Calculating the PDC Adjustment for IP Stays and SNF Stays: the two assumptions, removal of stay days from the numerator and denominator, shifting of overlapping supply to uncovered days after the stay, exclusion when stays span the whole treatment period, and inpatient stay Examples 1 and 2 (Tables L-6 to L-9).
Canonical Identity
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