Reproductive & Menstrual Health

Why your cycle is a health signal

The menstrual cycle is not just a monthly period. It is a repeating hormonal sequence — one that prepares the body for a possible pregnancy and resets when that does not happen — and it reflects how several body systems are working together. Clinicians pay attention to cycles for the same reason they pay attention to blood pressure: a change in pattern can be the first visible sign of something else going on, from thyroid problems to stress, weight change, or a reproductive condition.

There is no single universal "normal," but there are well-established ranges. The Mayo Clinic describes a typical adult cycle as roughly 21 to 35 days from the first day of one period to the first day of the next, with bleeding usually lasting a few days up to about a week. Cycles are often more irregular in the first years after periods begin and again in the years approaching menopause. What matters most is knowing your own baseline — because a change from your pattern is more informative than a comparison with anyone else's.

Understanding your cycle

A sensible starting point is the shape of the cycle itself: what counts as a normal menstrual cycle length, how long a period usually lasts, and what qualifies as an irregular period and what can cause it. When a period arrives later than expected, our guide to why a period might be late covers the common and often benign explanations alongside those that deserve a check-up.

Cycles also carry fertility information. Learn how ovulation and the fertile window work, which physical signs of ovulation some people notice, and practical ways to track your menstrual cycle — useful whether you are trying to conceive, avoiding pregnancy, or simply want a record to show a clinician.

Pain, bleeding, and conditions worth knowing

Cramping around a period is common. Pain that keeps you home from work or school, does not respond to over-the-counter treatment, or worsens over time is a different matter and warrants assessment. Our guide to evidence-based period pain relief covers what helps and where the line sits.

Bleeding patterns matter too. ACOG treats bleeding between periods, bleeding after sex, and unusually heavy or prolonged bleeding as abnormal uterine bleeding — a symptom to investigate rather than tolerate. We cover what spotting between periods can mean and the causes of heavy periods. On the emotional side, we explain the difference between PMS and PMDD, a distinction that changes how symptoms are treated.

Two conditions account for a large share of irregular, heavy, or painful cycles. The WHO estimates that polycystic ovary syndrome affects 8 to 13 percent of women of reproductive age, and that up to 70 percent of affected women worldwide remain undiagnosed. Endometriosis affects roughly 10 percent of reproductive-age women and girls globally, according to the WHO, and is often diagnosed years after symptoms begin. Start with the basics of PCOS and the basics of endometriosis.

What people get wrong

"A 28-day cycle is the standard." It is an average, not a requirement. Anything in the typical range that is consistent for you is usually fine.

"Severe period pain is normal." Common is not the same as normal. Persistent, disabling pain is a recognized reason to investigate.

"You cannot get pregnant during your period." Sperm can survive for several days, and cycles vary, so pregnancy is possible — this is why the NHS advises contraception regardless of cycle timing.

When to see a healthcare provider

• Periods that stop for three months or more without an obvious cause such as pregnancy or a new contraceptive method.
• Bleeding so heavy you soak through protection hourly, pass large clots, or feel faint or breathless.
• Bleeding between periods, after sex, or any bleeding after menopause.
• Pain that is severe, worsening, or unrelieved by usual measures.
• Cycles that suddenly become irregular after years of predictability, or difficulty conceiving after about a year of trying — sooner if you are over 35.

The guides below go deeper into each topic, from cycle basics to specific conditions.

This page is general education and is not a substitute for individualized medical advice.