A cycle in the medical sense is a series of things that occur one after the other, and which are regularly repeated. When we talk about a woman’s cycle we normally mean her menstrual cycle. The menstrual cycle usually takes between 25 and 30 days. The cycle starts the first day the woman has her period and lasts until the next time her period starts. Hormones govern the changes that occur in the body during the menstrual cycle. A woman will ovulate in about the middle of the cycle, and will usually have her period two weeks later.