What is the menstrual cycle?
The menstrual cycle is a recurring series of hormonal and physical changes that prepares the body for the possibility of pregnancy. It begins on the first day of a period and ends the day before the next period starts. Cycle lengths typically fall somewhere between 21 and 35 days, though most commonly around 28 days. Variation between cycles — even for the same person — is entirely normal.
Using a period tracker over several months can help you recognise your own pattern, which is far more meaningful than comparing to an average.
Phase 1: The menstrual phase (roughly days 1–5)
The cycle officially begins on day one of your period. During this phase, the uterine lining that built up during the previous cycle sheds. Hormone levels — including oestrogen and progesterone — are at their lowest. Periods typically last between 3 and 7 days, though this varies.
Some people experience cramping, fatigue, or mood changes during this phase, often linked to the drop in hormones and prostaglandins released during shedding.
Phase 2: The follicular phase (roughly days 1–13)
The follicular phase actually overlaps with menstruation, beginning on day one and continuing until ovulation. During this time, the pituitary gland releases follicle-stimulating hormone (FSH), which encourages several follicles in the ovaries to mature. Typically, one follicle becomes dominant and produces increasing amounts of oestrogen.
Rising oestrogen causes the uterine lining to thicken in preparation for a potential fertilised egg. Many people notice rising energy levels and an improved sense of wellbeing as oestrogen climbs through this phase.
Phase 3: The ovulatory phase (roughly day 14 in a 28-day cycle)
Ovulation is triggered by a surge of luteinising hormone (LH). The dominant follicle releases a mature egg, which travels into the fallopian tube. Ovulation typically lasts only 12 to 24 hours, though the fertile window extends a few days on either side because sperm can survive in the reproductive tract for several days.
The timing of ovulation is the most variable part of the cycle. In a shorter cycle it may happen earlier; in a longer cycle, later. It does not reliably fall on day 14 for everyone. For more on identifying ovulation, see our guide to signs of ovulation.
Phase 4: The luteal phase (roughly days 15–28)
After ovulation, the ruptured follicle transforms into a structure called the corpus luteum, which releases progesterone. Progesterone maintains the uterine lining in case a fertilised egg implants. Oestrogen also remains elevated during this phase.
If pregnancy does not occur, the corpus luteum breaks down, progesterone and oestrogen levels fall, and the uterine lining begins to shed — starting the next menstrual phase. The luteal phase is typically the most consistent part of the cycle, lasting around 12 to 14 days for most people. Premenstrual symptoms such as bloating, breast tenderness, mood shifts, and fatigue are commonly experienced in the latter part of this phase as hormones decline.
What does a "normal" cycle look like?
There is a wide range of what is considered typical. Cycle lengths between 21 and 35 days are broadly normal, and period length can range from 2 to 7 days. Variation from cycle to cycle — including occasional cycles that are shorter or longer — is common. Stress, illness, significant weight changes, intense exercise, and other factors can all influence cycle timing temporarily.
What matters more than matching any average is understanding your own typical pattern. Tracking over 3 to 6 months tends to reveal your personal baseline more reliably than comparing a single cycle to a chart.
Why tracking can help
Tracking your cycle over time offers several practical benefits. It can help you anticipate your period, understand your fertile window, notice patterns in energy or mood, and identify changes worth discussing with a healthcare provider. Consistent tracking over multiple cycles is more informative than any single cycle because it reveals your individual rhythm rather than a textbook average.
Our free period tracker makes it simple to log your cycle and view your patterns over time.
Disclaimer
This guide is for informational and educational purposes only and is not medical advice, a diagnosis, or a substitute for professional care. Menstrual cycles, fertility, and pregnancy vary significantly between individuals. If you have concerns about your cycle, fertility, or pregnancy, consult a gynaecologist or healthcare provider.
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