Ovulation period refers to the date when eggs are released from a woman’s body and is also an important period for women to become pregnant. If you want to plan for pregnancy, it's important to know when ovulation begins.

In order to determine when ovulation begins, there are several measurement methods that can be used. For example, you can use a thermometer to measure your basal body temperature, which indicates when your body begins to increase in temperature, signaling ovulation.

You can also observe other symptoms during your menstrual cycle, such as breasts becoming more tender, headaches, fatigue, etc. These symptoms may also indicate the onset of ovulation.

However, please note that these methods are not always accurate, so it is best to consult a doctor or professional fertility counselor to confirm the accurate calculation method.