Understanding Your Menstrual Cycle: A Complete Guide

Key menstrual cycle facts

1. Menstrual phase (days 1-5): The uterine lining (endometrium) sheds because no fertilised egg has implanted. Oestrogen and progesterone levels are at their lowest point. Bleeding typically lasts 3-7 days, with an average blood loss of 30-40 mL per cycle according to ACOG guidelines. Many women experience cramping caused by prostaglandins that help the uterus contract.
2. Follicular phase (days 1-13): Overlapping with menstruation, the pituitary gland releases follicle-stimulating hormone (FSH), which stimulates 5-20 follicles in the ovaries to begin maturing. Rising oestrogen thickens the endometrium and often brings improved mood and higher energy levels. One dominant follicle emerges and prepares to release its egg.
3. Ovulation phase (around day 14): A surge of luteinising hormone (LH) triggers the release of a mature egg from the dominant follicle. The egg enters the fallopian tube and remains viable for 12-24 hours. This is the peak fertility window. Some women experience mild pelvic pain (mittelschmerz), increased libido, or a slight rise in basal body temperature during ovulation.
4. Luteal phase (days 15-28): The empty follicle transforms into the corpus luteum, which secretes progesterone to maintain the endometrial lining. Progesterone also raises basal body temperature by 0.2-0.5 °C. If fertilisation does not occur, the corpus luteum degrades after about 10-14 days, progesterone drops, and menstruation begins again.

Phase durations at a glance

Common PMS symptoms

1. Record the first day of bleeding: This is day 1 of your cycle. Mark it consistently every month to calculate your average cycle length over time.
2. Note flow intensity: Track whether your flow is light, moderate, or heavy each day. This helps identify changes that may warrant medical evaluation, such as menorrhagia (excessively heavy periods).
3. Log symptoms daily: Record physical symptoms (cramps, bloating, headaches) and emotional states (mood, energy, sleep quality) throughout your cycle. Patterns often emerge after 3-4 tracked cycles.
4. Track basal body temperature: Your resting temperature rises 0.2-0.5 °C after ovulation due to progesterone. Consistent tracking can confirm ovulation occurred and help refine future cycle predictions.
5. Observe cervical mucus: Fertile-quality mucus is clear, stretchy, and resembles raw egg white. This change signals approaching ovulation and is useful for both fertility planning and general cycle awareness.
6. Use our period calculator: Enter your last period date and average cycle length to get predictions for your next several cycles, including estimated ovulation and fertile window dates.

• Stress: Chronic stress elevates cortisol, which can suppress GnRH signalling and delay or prevent ovulation, leading to longer or missed cycles. Even short-term intense stress — such as exams, bereavement, or travel — can temporarily disrupt your cycle.
• Weight changes: Both significant weight loss and obesity can disrupt the hormonal balance needed for regular ovulation. Body fat plays a direct role in oestrogen production, so extremes in either direction affect the HPO axis.
• Exercise intensity: Very high training loads can cause hypothalamic amenorrhoea, where the body suppresses menstruation to conserve energy. This is especially common among endurance athletes, gymnasts, and ballet dancers.
• Age: Cycles tend to be more irregular during adolescence (the first 2-3 years after menarche) and perimenopause (the years leading up to menopause, typically starting in the mid-40s). The most regular cycles typically occur between ages 25 and 35.
• PCOS: Polycystic ovary syndrome affects 6-12% of reproductive-age women and is one of the most common causes of irregular periods and anovulation. It is characterised by elevated androgens, ovarian cysts, and insulin resistance.
• Thyroid disorders: Both hypothyroidism and hyperthyroidism can cause menstrual irregularities, ranging from very light to very heavy periods or absent periods altogether.
• Medications and contraception: Hormonal contraceptives, certain antidepressants, antipsychotics, and chemotherapy drugs can all affect cycle timing and flow. After stopping hormonal birth control, it may take several months for natural cycles to resume.

• Your cycles are consistently shorter than 21 days or longer than 35 days.
• You have not had a period for 90 days or more (and you are not pregnant, breastfeeding, or menopausal) — this is called amenorrhoea.
• Your periods suddenly become much heavier than usual, or you soak through a pad or tampon every hour for several consecutive hours.
• You experience severe pain that interferes with daily activities and does not respond to over-the-counter pain relief such as ibuprofen.
• You have bleeding or spotting between periods or after sexual intercourse.
• Your cycle length varies by more than 9 days from month to month for several consecutive cycles.

• Maintain a balanced diet rich in iron, calcium, magnesium, and B vitamins. Leafy greens, whole grains, legumes, and lean protein support hormonal health. During menstruation, iron-rich foods help replace blood loss.
• Stay active with regular moderate exercise — 150 minutes per week as recommended by the WHO. Physical activity reduces PMS symptoms, eases cramps through improved blood flow, and helps regulate the cycle, but avoid overtraining.
• Prioritise sleep: aim for 7-9 hours per night. Poor sleep disrupts cortisol, melatonin, and reproductive hormones. Maintaining a consistent sleep schedule is especially important during the luteal phase.
• Manage stress through relaxation techniques such as meditation, yoga, progressive muscle relaxation, or deep breathing exercises. Even 10-15 minutes daily can lower cortisol levels.
• Stay hydrated — adequate water intake (around 2 litres per day) can help reduce bloating, headaches, and fatigue associated with PMS.
• Consider omega-3 fatty acids: research suggests they may help reduce menstrual pain and inflammation. Good sources include fatty fish, flaxseeds, chia seeds, and walnuts.
• Limit caffeine and alcohol during the luteal phase, as both can worsen PMS symptoms in some women. Caffeine may increase breast tenderness, while alcohol can exacerbate mood changes.