The Assessment Reference Date (ARD) is the anchor for every lookback window on the MDS. Under PDPM, the 5-day scheduled assessment's ARD must fall on days 1–8 of the Part A stay — but where exactly you place it inside that window can swing the per-diem materially.
Lookback windows you need to know
| Section | Lookback | Why it matters for PDPM |
|---|---|---|
| Section GG (function) | Days 1–3 | Drives PT/OT function score |
| Section O (services) | 7 days | IV meds, respiratory, dialysis |
| Section K (swallowing) | 7 days | SLP component |
| Section I (diagnoses) | 7 days active | NTA + clinical category |
A worked example
Patient admitted Monday with new IV antibiotics scheduled to end Thursday. Setting the ARD on day 8 captures the IV med service (Section O) and the diagnosis in Section I — both worth points. Setting the ARD on day 3 misses Section O entirely.