How to accurately determine your ovulation period If you want to get pregnant successfully or make a contraceptive plan, it is very important to know your ovulation period. Here are some ways to help you determine your ovulation period: 1. Pay attention to the menstrual cycle. The menstrual cycle usually lasts from 21 to 35 days. The first day is the first day of menstruation, and the last day before the second menstrual period is the cycle. Ovulation usually