Free tool
PDC and fail date calculator
Enter a patient's fill dates and days' supply for one medication. The calculator returns their Proportion of Days Covered (PDC) so far, their projected PDC if they never refill, and their fail date: the last day they can refill and still finish the measurement year at the 80% adherence threshold Medicare Part D Star Ratings use.
How it's calculated
PDC is the share of days in the treatment period a patient had the medication on hand. The treatment period starts at the first fill and ends at the end of the measurement year. Overlapping supply from an early refill is shifted forward, so a day is never counted twice. The fail date is the last refill date that leaves the patient at or above the threshold by year end, assuming they stay covered after refilling. The Pharmacy Quality Alliance defines the measure; Medicare Part D Star Ratings use it for statins, RAS antagonists, and diabetes medications.