The menstrual cycle is divided into four stages:
Menstrual phase: The uterine lining is shed through the vagina.  Oestrogen and progesterone levels drop. This stage usually lasts between three and seven days, although some women experience longer menstrual periods.
Follicular phase: This phase starts on the day your period starts, meaning there is some overlap with the menstrual phase, and finishes when you ovulate. During this phase, the egg is maturing and this sets off a surge of oestrogen to start thickening the womb lining. This phase lasts for 16 days on average, but can range from 11 to 27 days.
Ovulation phase: The mature egg is released from the ovary. At this phase of the cycle, it is possible to get pregnant. This happens on day 14 of a 28-day cycle.
Luteal phase: Oestrogen and progesterone levels rise, causing the womb lining to thicken, ready to receive a fertilised egg. If pregnancy doesn’t happen, hormone levels drop ahead of menstruation. You may experience PMS symptoms during this phase, which lasts for an average of 14 days.
Each stage varies from woman to woman and this can change over time.