What PDC is
Proportion of Days Covered is a claims-based adherence measure. For a given medication over a measurement window, it divides the number of days the patient had the drug on hand (from fill and refill dates) by the total days in the window, expressed as a percentage.
The widely used threshold is 80%: a patient with a PDC at or above 80% for a chronic medication is considered adherent. PDC is calculated for high-impact drug classes such as statins, diabetes medications (RASA and non-insulin diabetes drugs), and blood-pressure medications, the same classes that appear as Medicare Star Ratings adherence measures.
PDC improves when patients refill on time. Rivvi runs refill and adherence outreach as real two-way conversations from a branded pharmacy number, reminding patients before they run out, resolving pickup and refill barriers, and honoring opt-out, so more patients stay above the 80% line.
PDC, answered
How is PDC calculated?
PDC divides the number of days a patient had a medication on hand (derived from prescription fill and refill dates) by the number of days in the measurement period, expressed as a percentage. It is computed per drug class and, when a patient takes multiple drugs in a class, uses the combined covered days.
What is a good PDC score?
A PDC of 80% or higher is the standard threshold for being considered adherent to a chronic medication. Medicare Star Ratings adherence measures count the share of eligible members who reach that 80% threshold for statins, diabetes medications, and blood-pressure medications.
How is PDC different from MPR?
PDC and the Medication Possession Ratio (MPR) both estimate adherence from fill data, but PDC counts covered days without letting overlapping early refills inflate the score above 100%, so it is more conservative. PDC is the measure CMS uses for Star Ratings adherence.
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