Ovulation refers to the process of maturation and release of female eggs, which usually occurs between the 14th and 16th days of the menstrual cycle. However, for some women, the process can be a little bumpy, as factors such as irregular menstruation or ovarian disease can affect a woman's menstrual cycle and ovulation. Therefore, for these women, how to calculate ovulation may be a bit confusing.

Therefore, for those who know their menstrual and ovarian cycles, calculating ovulation may be relatively easy. However, for those who are unaware of their medical condition, it is best to consult a physician or professional health care provider for more specific advice and guidance.

To sum up, for most people, calculating ovulation starts from the first day of menstruation. However, for some women, the process can be a bit bumpy, so it's best to consult a doctor or professional healthcare provider for more specific advice and guidance.