hillmaker is a Python package that computes time-of-day and day-of-week-specific arrival, departure, and occupancy statistics from transaction data containing arrival and departure timestamps. Typical use is for capacity planning problems in places like hospital emergency departments, surgical recovery rooms, or any system in which entities arrive, occupy capacity for some amount of time, and then depart. It gets its name from the hill-like nature of summary occupancy plots -see Figure 1.