PeriWise
In short
- Perimenopause is the transition before menopause — it often starts in the early-to-mid 40s, sometimes in the late 30s.
- It is diagnosed by symptoms and cycle changes, not by a single hormone test — hormones fluctuate too much day to day.
- Symptoms commonly last years, not weeks. In one large US study the median duration of hot flashes was 7.4 years.
- Menopause itself is one day: twelve months after the final period. Everything before it is perimenopause.
Most of us grew up with a single word — “menopause” — for something that is really two chapters. Menopause is a date in hindsight: the point twelve months after your final period, reached on average around age 51–52. Perimenopause is everything before it — the years in which hormone levels start to swing, cycles change, and symptoms appear while you are still having periods.
That mismatch between the word and the experience is why so many women are blindsided. You can be 42, having regular-ish periods, and still be deep in the transition. Large cohort studies presented in 2025 suggest exactly this: many women with clear biological signs of perimenopause are never identified as being in it — by their clinicians or by themselves.
When does it start, and how long does it last?
There is no starting gun. For most women the first changes appear in the early-to-mid 40s; for some, in the late 30s. The length varies enormously — a few years for some, a decade for others. The often-cited SWAN study (Study of Women’s Health Across the Nation) found that among women with frequent hot flashes, the median total duration was 7.4 years — and for women whose symptoms began while cycles were still regular, 11.8 years.
Why a blood test rarely settles it
During perimenopause, estrogen and FSH don’t decline in a straight line — they spike and crash, sometimes within the same month. That’s why guidelines such as the UK’s NICE guideline advise diagnosing the transition in women over 45 from symptoms and cycle history, not lab values. A “normal” hormone result on a Tuesday doesn’t mean the transition hasn’t begun.
What it can look like
Hot flashes and night sweats are the famous ones — up to about 80% of women experience them. But the transition can also show up as sleep that breaks at 3 a.m., mood swings, anxiety, brain fog, joint aches, heart palpitations, dry skin, digestive changes and cycles that shorten, lengthen or skip. No two women get the same set, which is exactly why tracking your own pattern is so useful: it turns “something is off” into something you can describe.
The one-sentence version
Perimenopause is a normal, often long transition that deserves to be recognized while it is happening — not years later, in hindsight. Naming it is frequently the single most reassuring step.
Frequently asked questions
Can perimenopause start while my periods are still regular?
Yes. Symptoms like night sweats, sleep changes and mood shifts can begin while cycles are still fairly regular. Cycle changes often come later.
Do I need a hormone test to know I'm in perimenopause?
Usually not. Because hormones fluctuate sharply during the transition, guidelines such as NICE recommend diagnosing by symptoms and cycle history in women over 45. Testing has a role in specific situations — for example, suspected premature ovarian insufficiency.
How long will it last?
It varies widely. Studies suggest symptom durations of several years are common; in the SWAN study the median duration of frequent hot flashes was 7.4 years.
See your own pattern
PeriWise is a private iOS app for tracking perimenopause symptoms — logging is free, your data never leaves your iPhone, and doctor-ready PDF reports are always included. Get the app or browse Things That Helped.
Sources
Everything above is our own writing. The facts come from these sources — always read the originals:
- Avis NE et al., “Duration of menopausal vasomotor symptoms over the menopause transition” (SWAN), JAMA Internal Medicine, 2015 — https://pubmed.ncbi.nlm.nih.gov/25686030/
- NICE Guideline NG23 — Menopause: identification and management (updated November 2024) — https://www.nice.org.uk/guidance/ng23
- The Menopause Society — 2025 Annual Meeting research highlights — https://menopause.org/
- SWAN — Study of Women's Health Across the Nation — https://www.swanstudy.org/