Most women can name the end of this. Twelve months without a period, and you're through. What almost nobody can name is the beginning — and the beginning is where you probably are right now, possibly for the next several years.
Here is the thing that makes perimenopause so disorienting: it does not announce itself. There is no test that catches the first day. What there is, instead, is a staging system that researchers spent years building, and once you see it, a lot of scattered symptoms stop looking scattered.
The staging system
In 2011, a group of reproductive scientists met and produced what is now called STRAW+10 — the Stages of Reproductive Aging Workshop, ten years on from the first version. It's the closest thing we have to a map, and it's built almost entirely around one thing: your menstrual cycle.
The map has three phases that matter to you.
Late reproductive stage. Your cycles are still regular but something has shifted. They may be shorter than they used to be — a 28-day cycle quietly becoming 25. Flow may change. Fertility is declining. Most women notice nothing at all here, or notice and dismiss it.
Early menopausal transition. This is the official start of perimenopause, and it has a specific definition: a persistent difference of seven days or more between consecutive cycle lengths. Not one odd month. A pattern that recurs. If your cycles used to arrive at 28 days and now they come at 26, then 34, then 27, then 36 — that's the marker. It's the only reliable one there is.
Late menopausal transition. You go 60 days or more without a period. Then it comes back. Then it goes again. This stage typically runs one to three years, and it's when hot flushes and night sweats are usually at their worst.
Then twelve months of nothing, and you're postmenopausal.
What that means in practice
The definition of the start is a change in variability, not a change in symptoms. That's why so many women get told they're too young, or too regular, or too something. They've gone in describing sleep and rage and a strange new anxiety, and the conversation goes straight to stress or thyroid, because the cycle question never got asked properly.
It also means something practical: if you have not been tracking your cycle lengths, you have no way of knowing where you are on this map. Not because tracking is virtuous, but because the entry criterion is literally a comparison between consecutive cycles. Three or four months of dates is enough to start answering the question.
Be the first to know when we launch.
We'll only email you about the launch. See our privacy policy.
Why hormone tests usually don't help
The obvious response is to ask for a blood test. In most cases the answer will be no, and the reason is good.
During perimenopause, follicle-stimulating hormone rises — but it doesn't rise smoothly. It swings. You can be firmly in the transition and get a completely normal reading because you happened to have blood drawn on a good week. NICE guidance for the UK is explicit: for women over 45 with symptoms, do not use FSH to diagnose perimenopause or menopause. The clinical picture is more reliable than the number.
There are exceptions. If you're between 40 and 45 with symptoms and a change in your cycle, FSH may be considered. If you're under 40, testing matters a great deal, because premature ovarian insufficiency is a different situation with different consequences.
The age question
The World Health Organization puts natural menopause between 45 and 55 for most women worldwide, with the average landing around 51 in the UK and US. Perimenopause runs ahead of that — commonly starting in the mid-forties, not uncommonly in the early forties, occasionally in the late thirties.
Which means that if you are 43 and something has changed, you are not too young. You are, statistically, right on schedule.
Where to start
You need three things before this becomes legible: the length of your last few cycles, a list of what's changed in the past year that you'd previously filed under "stress", and a sense of when the changes started relative to each other.
That's not a diagnosis. It's the raw material for one — and it's the thing most likely to change the shape of a conversation with a clinician, because it moves you from "I feel off" to "here is a pattern".
Sources
- Harlow SD, Gass M, Hall JE, et al. Executive summary of the Stages of Reproductive Aging Workshop +10: addressing the unfinished agenda of staging reproductive aging. Menopause. 2012;19(4):387–395. - National Institute for Health and Care Excellence. Menopause: identification and management (NG23). Published 2015, updated 2024. nice.org.uk/guidance/ng23 - World Health Organization. Menopause fact sheet. 16 October 2024. who.int/news-room/fact-sheets/detail/menopause