What is perimenopause? What it feels like, when it starts and how long it lasts

Is this perimenopause, and is what I'm feeling normal?

Maybe your cycles have shifted. Maybe your sleep has got worse, you wake up drenched, or your mood feels less steady than it used to. If you're in your 40s, perimenopause is a reasonable explanation.

It is the transition before menopause, not a single event. It is a common, expected life stage, and no two people go through it the same way. One review suggests the hormonal changes of perimenopause may begin in regularly menstruating women in their mid-thirties, before periods visibly change, which is why it is easy to miss.¹ This article covers what perimenopause is, when it starts, how long it lasts, what it feels like and when to get checked.

What is actually happening in your body?

Perimenopause is defined mainly by changes in cycle regularity, using a research standard called STRAW+10 (a staging system for reproductive ageing). The early transition begins when your cycle length becomes more variable. The late transition is marked by longer gaps between periods². It ends at menopause, which is diagnosed after a full year without a period.

Hormones don't simply decline. They swing. Estradiol (the main estrogen) can run higher or lower than normal. FSH (follicle-stimulating hormone, the brain signal that prompts your ovaries to mature an egg) spikes. Progesterone tends to be lower in cycles where ovulation is weaker. Large studies show FSH starts rising years before the final period, while estradiol only begins falling closer to it.³

This differs from menopause, where estrogen stays consistently low. This may help explain why symptoms can start before your periods change.

Ovulation still happens during this stage, including close to the final period⁴. Pregnancy remains possible.

When does perimenopause start, and how long does it last?

Timing varies from person to person. Smoking is linked to an earlier start and a shorter transition⁵.

In SWAN, the median transition ran from about 4.4 years in women with the latest onset to about 8.6 years in those with the earliest. The earlier it started, the longer it lasted⁵.

Large studies suggest the final period typically arrives in the early 50s across ethnic groups.⁶

The label "perimenopause" may also understate how long symptoms last. Frequent hot flushes often last many years and commonly continue after the final period⁷.

What can perimenopause feel like?

Cycle changes come first for many women. Cycles may get shorter, longer or skipped. In one long-running study, average cycle length trended above 35 days and the running range of cycle lengths widened to about 42 days as the final period approached⁴. Some perimenopausal women have heavy flow that lasts for months and needs medical help.

Hot flushes and night sweats are among the common symptoms associated with menopause⁸. Poor sleep also becomes more common in perimenopausal women⁹.

Mood is also affected. Women are more likely to have a major depressive episode in perimenopause or early postmenopause than before it, regardless of past depression history¹⁰. Vaginal dryness and painful sex are also common, and symptoms tend to worsen as menopause approaches⁹.

There is no single normal pattern. Burden varies by individual and ethnicity. Hot flushes tend to last even longer in some groups, including African American women⁷.

How is perimenopause recognised, and do I need a blood test?

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For otherwise healthy women aged 45 or over, NICE (the UK's national guidance body) says diagnosis comes from symptoms and cycle history alone, with no lab tests¹¹. FSH is not useful because it fluctuates, and a single result can't rule perimenopause in or out.

NICE suggests considering FSH only at 40 to 45 with symptoms and a cycle change, or under 40 if menopause is suspected¹¹. If menopause is suspected under 40, NICE says premature ovarian insufficiency is diagnosed from symptoms plus raised FSH on two blood samples taken 4 to 6 weeks apart, never from a single test⁸. In the Massachusetts Women's Health Study, no single FSH value cleanly separated the stages, and the often-used 40 IU/L cutoff was inappropriate on its own¹².

Recognition is harder if something hides your cycle. Hormonal contraception and some surgeries make the usual bleeding and FSH clues unreliable. If that applies to you, your doctor may lean more on your age and symptoms, though evidence for these groups is limited.

What don't we know yet?

Duration figures vary. SWAN gives 4.4 to 8.6 years, depending on when the transition starts⁵. The answer also depends on whether hot flushes count.

Large studies mostly enrolled women already in their 40s, so women whose transition begins in their 30s are under-represented. "Typical" may therefore skew late and short. Evidence is also thinner for women on hormonal contraception, after hysterectomy or endometrial ablation, and for non-US and non-White populations.

Researchers still debate whether brain fog, anxiety and joint pain come from hormones, ageing, or sleep loss and life stress. STRAW+10 predates research on AMH (a marker of ovarian reserve), and a revision is considered overdue.

When should you talk to your doctor?

Book an appointment if bleeding is very heavy, comes much more often than usual, or lasts much longer than usual. The same applies if heavy flow continues for several months. Heavy bleeding is still worth assessing.

Get help if symptoms are severe or disrupting your life, whether that's sleep, mood or hot flushes. Depression risk is higher in this stage, so persistent low mood deserves attention¹⁰. If you are in crisis or having thoughts of harming yourself, contact emergency services or a crisis line right away.

Also see a doctor if symptoms start before 40. Ovulation can continue throughout perimenopause⁴, so pregnancy is still possible — talk to your doctor about contraception.