The objective of the present invention is to provide a program for highly reliable ovulation day prediction. The ovulation day prediction program causes a computer to execute a process for calculating predicted ovulation day data in accordance with a specific menstrual cycle by means of applying a specific menstrual cycle to the relationship between the average menstrual cycle and the spacing between days of menstruation and days of ovulation inferred on the basis of data of a plurality of people acquired ahead of time.
