No! The day of ovulation can vary among women as well as within each individual woman. However, once a woman ovulates, the time between ovulation and her menstruation is very consistent, almost always between 12 and 16 days. Within most individual women, this length of time generally doesn’t change by more than a day or two. In other words, if there is going to be variation in the cycle, it is the first preovulatory phase that may vary. The second (postovulatory) phase generally remains constant.