How to Master the Fertility Cycle To successfully conceive, it is very important to accurately grasp the fertilization cycle. The following will introduce in detail how to calculate the accurate time of conception from four aspects. 1. Understand the menstrual cycle. The menstrual cycle of different women will be different, usually around 28 days, but it may also be between 26-30 days. The first day is the day when menstruation starts, and the 14th day is the day of ovulation. The time for the egg to be fertilized is generally after ovulation.