🔬 Key Takeaways
- Your cycle has four phases: menstrual, follicular, ovulation, and luteal
- Each phase is governed by different hormones — oestrogen, FSH, LH and progesterone
- Understanding your cycle predicts energy, skin, mood and appetite shifts
- Normal cycles range from 21 to 35 days — not just 28
- Tracking your cycle is one of the most powerful health tools available
Most of us were taught the basics of the menstrual cycle in school — and most of us were taught badly. The rigid "28-day clock" model leaves out the complexity that actually explains why you feel energised one week and depleted the next. Let's fix that.
Your menstrual cycle is one of the most sophisticated hormonal systems in the human body. It is not just about your period. It is a monthly rhythm that affects your skin, energy, brain, appetite and immune system. Understanding it is genuinely one of the most empowering things you can do for your health.
Phase 1: Menstrual Phase (Days 1–5)
Day 1 of your cycle is the first day of your period — this is the medical definition. During this phase, both oestrogen and progesterone are at their lowest. The uterine lining sheds because pregnancy did not occur. Prostaglandins trigger uterine contractions, causing cramping. Iron levels may dip if your flow is heavy — a key driver of fatigue. Read more in our post on why you feel tired all the time.
Emotionally, low hormones mean you may feel more inward and slower. This is biology, not weakness. Rest is genuinely supported by your physiology during this phase.
Phase 2: Follicular Phase (Days 6–13)
As your period ends, the pituitary gland releases follicle-stimulating hormone (FSH), stimulating several follicles in the ovaries. One becomes dominant and produces rising oestrogen. This oestrogen rebuilds the uterine lining, boosts serotonin, improves skin clarity and increases cognitive sharpness.
This is typically the phase where women feel their best — energetic, social, motivated and clear-headed. Your skin often looks its best here too, because rising oestrogen supports collagen and hydration. For the full picture, see our post on why your skin changes during your cycle.
Phase 3: Ovulation (Around Day 14)
A surge in luteinising hormone (LH) triggers the dominant follicle to rupture and release a mature egg. Oestrogen peaks just before ovulation, giving many women a noticeable lift in confidence, libido and energy. Body temperature rises slightly after ovulation — useful for tracking. The fertile window spans roughly days 11–17 in a 28-day cycle.
Phase 4: Luteal Phase (Days 15–28)
After ovulation, the empty follicle becomes the corpus luteum and produces progesterone. Progesterone prepares the uterine lining for potential implantation. If no fertilisation occurs, the corpus luteum degenerates, progesterone drops and your period begins.
PMS symptoms — bloating, breast tenderness, mood changes, breakouts and fatigue — are real physiological responses to this hormonal shift, not psychological weakness. For nutrition support during this phase, see our guide on what to eat in each phase of your cycle.
Why Your Cycle Isn't Always 28 Days
The 28-day cycle is an average, not a rule. Normal cycles range from 21 to 35 days. What varies most is the follicular phase length. The luteal phase is relatively fixed at 12–14 days. Stress, illness, weight changes and sleep disruption all affect cycle length by influencing the hormonal signals governing follicle development. According to NHS guidance, persistently irregular cycles are worth discussing with a doctor.
How to Start Tracking Your Cycle
Note: Day 1 (first day of period), last day, and how you feel daily — physically and emotionally. Over 2–3 cycles, patterns emerge. You may notice worse sleep in the luteal phase, breakouts around Day 22, or peak creativity in the follicular phase. This information gives you back agency over your own body.
"Your cycle is not an inconvenience. It is a monthly health report — if you know how to read it."
When to Seek Medical Advice
Certain symptoms warrant a doctor visit: cycles consistently under 21 days or over 35 days, extremely heavy bleeding (soaking a pad in under an hour), severe pain disrupting daily life, or cycles stopping altogether. These may indicate PCOS, endometriosis, thyroid dysfunction or other conditions.
