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The menstrual cycle is a natural process a woman’s body undergoes regularly as it prepares for the possibility of pregnancy. Typically beginning between ages 12 and 15, this monthly cycle continues until menopause, usually around age 52.

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The menstrual cycle is counted from the first day of one period to the first day of the next. It is governed by changing hormone levels that control the shedding and rebuilding of the uterine lining.

During the cycle, the lining of the uterus thickens in anticipation of a fertilized egg. Around mid-cycle, ovulation occurs — an egg is released from one of the ovaries, marking the peak fertility window, which lasts roughly 5 days before through 1-2 days after ovulation.

If fertilization doesn't happen, hormone levels drop, and the uterine lining sheds, resulting in menstrual bleeding that typically lasts 2 to 7 days — commonly referred to as a period.

Across individuals, cycle length varies widely but is generally around 28 days. Regular cycles usually show a variation of fewer than 8 days between shortest and longest cycles.

Menstruation pauses during pregnancy and early breastfeeding and eventually ceases permanently during menopause, defined as no menstrual bleeding for a full year.

Understanding the menstrual cycle is helpful not just for family planning but also to recognize normal patterns and identify potential health issues. Tools like a Period Calculator can estimate menstrual dates and probable ovulation days, providing a calendar view to help women track their cycles and fertility windows.

Hormonal interplay between the brain’s pituitary gland and the ovaries orchestrates the phases of the cycle:

Menstrual Phase: Shedding of the uterine lining if no pregnancy occurs.
Follicular Phase: Building of the uterine lining and maturation of an egg follicle.
Ovulation: Release of the mature egg for fertilization.
Luteal Phase: Preparation of the uterine lining for possible implantation.

Every woman's cycle is unique and can change over time due to factors like age, stress, health, and lifestyle. Tracking your cycle helps deepen body awareness and supports reproductive health.