It is an object to estimate an ovulation date using less menstrual cycles of body temperatures while preventing decrease in estimation accuracy. An information processing device obtains the equation of a function that approximates the relationship between body temperature data and dates. The information processing device determines a low-temperature-phase reference body temperature, based on a plurality of days of body temperature data identified based on the date corresponding to a local minimum value in the function, and determines a high-temperature-phase reference body temperature, based on a plurality of days of body temperature data identified based on the date corresponding to a local maximum value in the function. Then, the information processing device estimates an ovulation date in the current menstrual cycle, based on a determination reference body temperature set at a value between the low-temperature-phase reference body temperature and the high-temperature-phase reference body temperature and on measurement data.
