Is it normal to have early periods every month?

Note on the name: in May 2026, polycystic ovary syndrome (PCOS) was formally renamed polyendocrine metabolic ovarian syndrome (PMOS), following a global consensus process. The old name was inaccurate — the condition affects multiple hormone and metabolic systems, not just the ovaries, and "polycystic" wrongly implies ovarian cysts. Nothing about the condition, its diagnosis or its treatment has changed. Both names will be used side by side for the next few years, and we use PCOS below since that is the term most people know.

A normal menstrual cycle runs between 24 and 38 days, counted from the first day of one period to the first day of the next. This range comes from FIGO's menstrual terminology system, which replaced the older 21–35 day definition you may still see quoted in many places online. If your cycle is consistently shorter than 24 days, that is termed frequent menstruation — the older word was polymenorrhoea — and it is worth having looked at. Common reasons include thyroid problems, PCOS, approaching menopause, or a short luteal phase (the second half of the cycle). Some variation is entirely normal. Cycles are still considered regular if the gap between your shortest and longest cycle stays within about 7 to 9 days, and that acceptable variation widens slightly with age. If your periods are arriving less than 24 days apart month after month, see a gynaecologist. A cycle diary, blood tests, and a pelvic ultrasound are the usual starting point.