For something that shapes so much of our lives, the menstrual cycle is remarkably under-taught. Most of us left school knowing that a period happens roughly once a month, and very little else. But your cycle is not a single event; it is a four-phase hormonal rhythm that influences your energy, mood, sleep, metabolism, skin, and cognition across the entire month.
Understanding is one of the most powerful forms of health literacy you can build.
What Actually Is the Menstrual Cycle?
The menstrual cycle is the monthly sequence of hormonal changes that prepares the body for a potential pregnancy. It is coordinated by a conversation between the brain (hypothalamus and pituitary gland) and the ovaries, mediated by four key hormones: oestrogen, progesterone, follicle-stimulating hormone (FSH), and luteinising hormone (LH).
A typical cycle lasts 21 to 35 days. Day one is the first day of your period and the cycle ends the day before your next period begins. "Regular" does not necessarily mean 28 days; regular means predictable for you.
The Four Phases
1. Menstrual Phase (Days 1–5, approximately)
If pregnancy has not occurred, oestrogen and progesterone drop, triggering the shedding of the uterine lining. Energy is often lower, and iron stores take a small hit with blood loss. This is a phase for rest, not pushing through.
2. Follicular Phase (Days 1–13, overlapping with menstruation)
FSH rises, stimulating follicles in the ovaries to mature. Oestrogen climbs steadily, which tends to lift mood, sharpen cognition, and increase energy and motivation. Many people feel at their most capable in the late follicular phase.
3. Ovulation (Around day 14 in a 28-day cycle)
A surge in LH triggers the release of a mature egg from the ovary. Oestrogen peaks, testosterone sees a brief rise, and libido often follows. The fertile window spans roughly the five days before and the day of ovulation.
4. Luteal Phase (Days 15–28, approximately)
The ruptured follicle becomes the corpus luteum, which produces progesterone. Progesterone raises basal body temperature, calms the nervous system, and prepares the uterine lining. If pregnancy does not occur, both hormones fall sharply in the final days, often producing PMS symptoms, before the cycle restarts.
Why Cycle Literacy Is Crucial
Tracking your cycle is not only relevant for those trying to conceive or avoid pregnancy. Cycle patterns are a window into broader health. Consistently short cycles, very long cycles, missing periods, or dramatic shifts in flow or symptoms can flag thyroid dysfunction, PCOS, perimenopause, stress-related amenorrhoea, or nutrient deficiencies.
Knowing your pattern also lets you work with your physiology rather than against it: scheduling demanding work in the follicular phase, protecting rest during menstruation, and recognising that low mood in the late luteal phase is often hormonal, not personal.
When to Seek Support
Cycles that are consistently shorter than 21 days or longer than 35, periods heavy enough to soak through protection hourly, pain that disrupts daily life, or the absence of periods for three or more months all warrant a conversation with a clinician. These are not symptoms to normalise.
Your cycle is talking to you every month. Learning its language is one of the most practical acts of self-knowledge you can practise.