Ovulatory period is the second phase of the menstrual cycle. A single, mature egg from a follicle that developed in the ovary released in this period. In average, the time from the beginning of the last menstrual period until ovulation is 14.6 days.
Once released, the egg is capable of being fertilized for about 1 to 3 days before it begins to disintegrate. A woman is fertile several days before ovulation, because the sperm could survival in woman’s body for 3 to 5 days. So there are almost 10 days in menstrual cycle is fertile. We defined them as ovulatory period.
Even though we know the average gap from last menstrual bleeding to ovulation is 14.6 days, it is still very difficult to predict when will it occur. The gap is varied between women and between cycles in any single woman. Without physic test, we can only guess it. That’s why somebody get pregnant while she only had sexual intercourse in her “safe period“.