Why your cycle length changes in perimenopause

Shorter, then longer, then skipped. The sequence is common, and it is usually the first sign.

For most people the earliest sign of perimenopause is not a hot flash. It is the calendar.

The usual sequence

Shorter first. Cycles often contract by a few days — a 29-day cycle becoming 25 or 26. This can begin years before anything else changes, and it is easy to miss without a record.

Then variable. Some months short, some long. This is the phase clinicians call early perimenopause, and variation of more than seven days between cycles is the common marker.

Then skipped. Gaps of 60 days or more mark the late transition. Periods may return after a skip; that is expected and does not mean the transition has reversed.

Then stopped. Menopause is confirmed after twelve consecutive months with no period — and only in hindsight.

Why it happens

Ovulation becomes less regular. The follicular phase — the first half — shortens as the ovaries respond differently to hormonal signals, which shortens the whole cycle. Later, cycles where no egg is released produce long gaps.

Why this is hard to notice without tracking

The change is gradual and the memory is unreliable. Most people can say roughly how long their cycle was "normally" and cannot say what it has been recently. A year of dates makes the trend visible in a way that no amount of recollection does.

It also makes prediction genuinely harder, which is why an honest app widens its estimate rather than pretending to the same confidence it had before.

Still worth checking

Bleeding between periods, bleeding after sex, unusually heavy bleeding, or any bleeding after twelve clear months — none of those are simply "perimenopause", and all of them are worth an appointment.