An object is to provide programs for reliable predictions of the day of ovulation. A process is executed in a program for predicting a day of ovulation on a computer, the process including calculating a predicted ovulation day data corresponding to a particular menstrual cycle by applying the particular menstrual cycle to a relationship between a period between a menstrual day and a day of ovulation and an average length of a menstrual cycle, the relationship being estimated based on data of a plurality of persons which have been previously obtained.
