PDC Fail Date: How to Calculate It and When to Act

A PDC fail date is the last day a patient can refill and still reach 80% proportion of days covered for the year. To calculate it, count the days from first fill to December 31, take 20% as allowable gap days, subtract gap days already used, and add the rest to the day the supply runs out.

What a fail date is

PDC (proportion of days covered) is the share of days in the treatment period when the patient had medication on hand, based on pharmacy claims. The Pharmacy Quality Alliance (PQA) sets the passing threshold at 80% for most drug classes. Medicare uses PDC for its three Part D adherence measures: diabetes drugs, RAS antagonists and statins. See the PDC glossary entry for the basics.

The fail date is the point after which the math can't be saved. If the patient refills on the fail date and stays covered every day through December 31, they finish at 80% or a hair above. If they refill one day later, they finish below 80% no matter what they do next.

Three spec rules shape the calculation:

• The period starts at the first fill. PQA's treatment period runs from the first fill date to the end of the measurement year, or to death or an enrollment gap.
• Two fills are required. A patient needs at least two fills on different dates to be measured at all.
• The first fill must come at least 91 days before the period ends. Late-year starts drop out of the measure for that year.

The formula

"Day supply runs out" means the first day with no medication on hand. If a 90-day fill was picked up on March 1, the last covered day is May 29 and the first uncovered day is May 30.

Round the allowable gap days down. The patient needs at least 80% covered, so a fractional gap day is never available.

A worked example

Take a patient on a statin who first fills on March 1, 2027, for a 90-day supply. She has not refilled yet.

Step 1: Treatment period. March 1 through December 31 is 306 days. (March has 31, April 30, May 31, June 30, July 31, August 31, September 30, October 31, November 30, December 31. That totals 306.)

Step 2: Allowable gap days. 20% of 306 is 61.2. Round down to 61. She needs at least 245 covered days, and 245 divided by 306 is 80.07%.

Step 3: Supply runs out. The 90-day fill covers March 1 through May 29. Her first uncovered day is May 30.

Step 4: Fail date. She has used zero gap days so far. May 30 through July 29 is 61 uncovered days. If she refills on July 30 and stays covered, she ends the year at 245 of 306 days, or 80.07%. If she refills on July 31, she has 62 gap days and finishes at 79.7%.

Her fail date is July 30, 2027.

Now change one thing. Say she had started on January 1 instead. Her period would be 365 days and her gap budget 73 days. Starting later cost her 12 days of slack. This is why plan reports show different fail dates for patients who look alike.

For a patient who already has gap days on the books from a late refill earlier in the year, subtract them. With 10 gap days used, 51 remain, and the fail date lands 51 days after the current supply runs out instead of 61.

Plan reports and pharmacy adherence tools also handle edge cases, such as early refills that overlap the previous supply. Use your plan's fail date when you have it. Use this math to check it and to understand why it moved.

When to act: the intervention window

The fail date is the last possible day. Acting on it is too late in practice. A refill on the fail date still needs a prescription with refills left, a pharmacy with stock, and a patient who can pick it up. Any of those can take days.

There is no CMS rule for when to call. As practice guidance, a common approach aims for two moments:

1. Before the supply runs out. A check-in about a week before the last covered day prevents the gap entirely. For our patient, that is around May 23.
2. Four to six weeks before the fail date at the latest. If she hasn't refilled by then, outreach becomes urgent. For our patient, that window opens around June 18 and closes around July 2.

The weeks between the window and the fail date are for second attempts, prescriber callbacks for new prescriptions, and delivery.

A cadence you can copy

Here is a sample cadence for the patient above. Adjust the gaps to your volume and staff.

Any reply that resolves the case ends the sequence. A patient who says she refilled at another pharmacy, or whose prescriber stopped the drug, comes off the list with the reason recorded.

Running this at scale

The math is easy for one patient. It gets hard at a few thousand patients across three drug classes, with fills changing every day.

Rivvi is a HIPAA-compliant AI workspace. A pharmacy or plan team can upload a fill-history export or a plan adherence report, then ask Rivvi to compute treatment periods, gap budgets and fail dates, and sort the list by who needs a call first. On the Team plan the same workspace places the calls and texts in that cadence. Clinical questions go to a pharmacist by live warm transfer or as a task with the details. Opt-outs are honored on every path, and outcomes are recorded in Rivvi.

At Southeast Medical Group, Rivvi's refill outreach produced 56% refill success versus 5 to 10% with manual outreach, as of August 2026. See the full playbook in How to Improve PDC, or the workflow on the medication adherence page. For how adherence feeds plan ratings, read our Star Ratings guide and the Star Ratings solution.

Sources

• PQA, Measures resources (PDC definition and thresholds)
• PQA PDC-DR specification (via Florida Blue)
• Johns Hopkins Health Plans, Medication Adherence for Diabetes
• CMS, 2027 Star Ratings measures