on April 22, 2025
The menstrual cycle is one of the most reliable indicators of reproductive and overall health. It is a recurring pattern of hormonal and physical changes that prepares the body for a potential pregnancy each month. And yet, for something so central to female health, most of us were never taught to understand it properly.
Knowing your cycle is not just useful for family planning. It helps you understand your energy levels, mood, skin, sleep, and libido across the month. It gives you a framework for your body that most women find genuinely life-changing once they have it.
This guide covers all four phases of the menstrual cycle: what is happening hormonally, what you might feel, and what it means for your fertility.
How Long Is a Menstrual Cycle?
A menstrual cycle begins on the first day of your period and ends the day before your next period starts. The average cycle is around 28 days, but anywhere from 21 to 35 days is considered normal. Cycle length also varies from person to person and from cycle to cycle, which is why tracking your own data over time is far more useful than relying on averages.
The cycle is divided into two broad halves: the follicular phase (before ovulation) and the luteal phase (after ovulation). For clarity, it is most useful to think of it as four distinct phases.
Phase 1: The Menstrual Phase
The menstrual phase is the most visible part of the cycle. It begins on day 1 of your period and typically lasts between 2 and 7 days.
If the egg released in the previous cycle was not fertilised, oestrogen and progesterone levels fall. This hormonal drop signals the uterus to shed its lining, which leaves the body as menstrual blood. The uterine muscles contract to help expel the lining, which is what causes cramping.
During this phase, energy levels are often lower and the body benefits from more rest. This is not a weakness; it is a physiological reality. Giving yourself extra recovery time during your period is a form of body literacy, not indulgence.
Phase 2: The Follicular Phase
The follicular phase overlaps with menstruation and continues until ovulation. It typically lasts 10 to 14 days, though this varies.
During this phase, the pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the ovaries to develop a group of follicles. Each follicle contains an immature egg. As the follicles grow, they produce oestrogen, which rebuilds the uterine lining and creates a nutrient-rich environment in preparation for a potential pregnancy.
Eventually, one follicle becomes dominant and continues to grow while the others are reabsorbed. Rising oestrogen levels also trigger a surge in energy, mood, and mental clarity for many women. This is often the phase where you feel most like yourself.
Phase 3: Ovulation
Ovulation is the shortest phase of the cycle, lasting just 16 to 32 hours. It is also the most significant from a fertility perspective.
As oestrogen peaks, the pituitary gland releases a surge of luteinising hormone (LH). This LH surge triggers the dominant follicle to rupture and release the mature egg into the fallopian tube, where it can be fertilised by sperm. The egg survives for approximately 12 to 24 hours after release.
Ovulation typically occurs around day 14 of a 28-day cycle, but this varies considerably. Around 70% of women ovulate outside the expected day 13 to 15 window. Stress, illness, travel, and other factors can all shift ovulation timing, which is why calendar-based predictions are unreliable for many women.
Signs that ovulation may be approaching include a change in cervical mucus (becoming clear and stretchy, like raw egg white), a slight rise in libido, and occasionally a mild twinge or ache on one side of the lower abdomen known as mittelschmerz.
The fertile window extends beyond ovulation day itself. Because sperm can survive in fertile-quality cervical mucus for up to 5 days, the window for conception opens several days before ovulation occurs.
Tracking Ovulation with Basal Body Temperature
Basal body temperature (BBT) is one of the most reliable ways to confirm that ovulation has occurred. After ovulation, progesterone causes a measurable temperature rise of approximately 0.2 to 0.5 degrees Celsius, which remains elevated for the rest of the cycle.
Devices like Daysy and Lady-Comp measure your BBT each morning and use a self-learning algorithm to identify your fertile window and predict ovulation. Daysy signals your predicted ovulation day with a red flashing light, and the DaysyDay app lets you follow your temperature curve in detail across the cycle. Over time, the device learns your individual pattern and becomes increasingly precise.
Phase 4: The Luteal Phase
The luteal phase begins after ovulation and lasts until the start of your next period, typically 12 to 14 days. Unlike the follicular phase, the luteal phase is relatively consistent in length from cycle to cycle.
After the follicle releases its egg, it transforms into the corpus luteum, a temporary structure that produces progesterone. Progesterone prepares the uterine lining for implantation and maintains the pregnancy if fertilisation occurs. It also causes the characteristic rise in basal body temperature that confirms ovulation has taken place.
If the egg is not fertilised, the corpus luteum breaks down after around 10 to 14 days. Progesterone and oestrogen levels fall, triggering menstruation and the start of a new cycle.
The luteal phase is when PMS symptoms are most likely to appear: mood changes, bloating, breast tenderness, fatigue, and food cravings. These are driven by the hormonal shifts of this phase, particularly the decline in serotonin that accompanies falling oestrogen levels. Tracking your cycle helps you anticipate these changes and respond to them with more self-awareness and less confusion.
Why Understanding Your Cycle Matters
Your menstrual cycle is not just a fertility event. It is a monthly report on your hormonal health. Irregular cycles, very short or very long luteal phases, absent ovulation, or severe PMS can all be signs that something in your hormonal system needs attention.
Tracking your cycle over time, particularly your basal body temperature, gives you and your healthcare provider genuinely useful data. It can help identify conditions such as PCOS, thyroid dysfunction, or luteal phase defects that might otherwise go undetected for years.
The more you understand your cycle, the more agency you have over your own health.
A note from Period Wisdom Boutique
Period Wisdom Boutique exists because we believe women deserve to understand their bodies. Not in a clinical, overwhelming way, but in a way that feels personal, empowering, and genuinely useful in everyday life.
The menstrual cycle is a perfect place to start. Once you understand what is happening in each phase and why, you stop experiencing your body as unpredictable and start recognising its patterns. That shift from confusion to self-knowledge is exactly what we are here to support.
