Understanding Your Menstrual Cycle: When Does Period Bleeding Occur?

Menstruation (the period) is the visible phase of the menstrual cycle, but it's just one part of a tightly coordinated hormonal cascade.

Cycle Basics

• Day 1 = first day of menstrual bleeding.
• Average cycle length: 28 days (normal range: 21–35 days in adults; up to 45 days in young adolescents).
• Bleeding duration: Typically 3–7 days.

Phases of the Cycle

1. Menstrual Phase (Days 1–5/7): Estrogen and progesterone drop → uterine lining (endometrium) sheds → bleeding.
2. Follicular Phase (Days 1–13): FSH stimulates follicular growth; rising estrogen rebuilds endometrium. Ends with LH surge triggering ovulation.
3. Ovulation (~Day 14 in a 28-day cycle): Mature egg released; fertile window ~5 days before to 1 day after.
4. Luteal Phase (Days 15–28): Corpus luteum secretes progesterone to prepare endometrium for implantation. If no pregnancy, hormone levels fall → cycle restarts.

Key Points

• Cycle length varies mainly due to follicular phase duration; luteal phase is relatively fixed (~14 days).
• Irregular cycles are common in the first years after menarche and during perimenopause.
• Tracking apps or calendars help identify personal patterns and fertile windows.

See a clinician if cycles are consistently <21 or >35 days, bleeding exceeds 7 days, flow is very heavy (soaking ≥1 pad/tampon hourly), or periods stop for >90 days (not pregnant).