Treated Days form the backbone of treatment patterns analyses in IHD and allow users to look at metrics like adherence, medication switching, and trends in treatment. We have developed a set of measures in IHD focused on using treated days to analyze medication information, including Discontinuation, Continuous Treatment, Concurrent Treatment, Daily Dose, and Number of Treated Days. This chapter will explain the calculation of treated days and how they factor into your analysis of medications in IHD.