What is Ovulation Day? Ovulation day is a critical period in a woman\’s menstrual cycle, representing the time when the egg has matured and been released. Usually for women with a 28-day cycle, ovulation occurs approximately 14 days before menstruation begins. For women with irregular cycles, you can use the following methods to determine your ovulation period. How to determine the ovulation period 1. Through the body temperature method: The body temperature that rises during ovulation is a signal to determine the ovulation period. Basal body temperature can be measured at the same time every morning