The menstrual cycle

How a cycle works

The average cycle is about 28 days, but anything between 21 and 35 days is considered normal, and month-to-month variation is common. It has three phases: the follicular phase (from the first day of bleeding to ovulation), ovulation, and the luteal phase, which is more consistent at 12 to 14 days. Ovulation therefore happens roughly 14 days before the next period — not 14 days after the last one.

That detail matters practically: in anyone with irregular cycles, ovulation is unpredictable, which is why fertility-awareness methods are less reliable in everyday use (see contraceptive methods).

Period pain: where normal ends

Mild cramping on the first day, relieved by simple painkillers, is common. Pain that makes you miss school or work, that does not respond to usual treatment, or that comes with pain during sex or bowel movements and severe fatigue is not normal and should raise the possibility of endometriosis.

Premenstrual symptoms

Irritability, breast tenderness, bloating, fatigue and low mood in the days before a period affect a large share of women to varying degrees. Regular exercise, less salt and alcohol, and adequate sleep often help. A severe form with major mood impact — premenstrual dysphoric disorder — is recognised and treatable: it deserves a consultation rather than resignation.

Heavy, absent or irregular periods

• Very heavy bleeding (changing protection hourly, large clots, fatigue) risks anaemia and should be investigated — fibroids, polyps, clotting disorders, or a copper coil.
• No periods for more than three months outside pregnancy also warrants investigation: polycystic ovary syndrome, thyroid problems, significant weight loss, intense exercise, major stress.
• Bleeding between periods or after sex should always be checked, if only to exclude a cervical cause.

Products and safety

Tampons, menstrual cups, period pants and reusable pads: no option is inherently better, but internal products must be changed or emptied regularly — at most every 6 to 8 hours for tampons, and never left in overnight — because of the rare but serious risk of toxic shock syndrome. High fever, vomiting or a rash during a period means removing the product and seeking urgent care.

On cost: period poverty is a documented problem, and the response differs sharply from one country to the next — some have made free provision a legal duty, others distribute in schools and public services, and many have removed sales tax on period products altogether. The position where you live is set out country by country below.

What differs between countries

The biology of the cycle is universal; the price of products, free provision, menstrual leave and the recognition of endometriosis are not. The table sums it up country by country; a full page covers those with enough to say, and otherwise the link leads to the country's contraception page, which shows where to find gynaecology care.

This topic is also covered for French-speaking countries · German-speaking countries.

Further reading

• WHO — menstrual health — international framework and recommendations
• OMS / WHO — endométriose — international scientific reference on endometriosis

Links to official or reference sources. They open in a new tab.