Women's Issues: Trying to have a baby? You need to know the time of a menstrual cycle when a woman has released an ovum. Day one of the menstrual cycle is the first day of bleeding. The ovary releases an ovum on the 14th day of the cycle.
Keep in mind that humans are not robots. Nothing works out with such mathematical precision. There's at least a five-day range for the occurrence of ovulation. It can happen anytime between the cycle's 12th and 17th days.
On the day of ovulation, a woman's body temperature rises by half a degree or a little more. It remains elevated for the rest of the cycle.
To detect that rise, women need a special thermometer called a basal body thermometer. You can find it in a drug store.