What happens to your periods in perimenopause?

For most women, a change in periods is the first sign that anything is happening at all. The NHS puts it plainly: one of the first signs of perimenopause is usually a change to your periods — they may come more often or less often, and bleeding may get heavier or lighter.

What that description doesn't convey is how disorienting it is in practice. You've had roughly the same arrangement with your body for thirty years, and then it stops keeping to it — without telling you whether this is normal or something to worry about.

Mostly it's normal. Here's what changes, and the specific things that aren't.

What normally changes

How often they come. NHS inform describes periods usually becoming less frequent over a few months or years before stopping altogether — but the route there isn't a straight line. They can also arrive closer together for a while before spacing out. Skipping a month and then returning is common.

How heavy they are. They may become heavier or lighter, and for many women it's both, at different points. A heavier-than-usual period after months of light ones isn't a sign you've gone backwards.

How they end. For some women, periods stop suddenly rather than tapering.

Spotting between periods also happens, as hormone levels shift.

The single most useful thing to understand: unpredictability is the pattern. People arrive at this looking for the new normal, and there often isn't one until it's over.

Why it happens

The short version is that you stop ovulating reliably.

In a typical cycle, an egg is released and the hormones that follow give the cycle its structure and timing. In perimenopause, ovulation becomes hit-and-miss. Some months it happens, some months it doesn't — and a cycle without ovulation doesn't behave like a cycle with one. Oestrogen and progesterone fluctuate rather than declining smoothly.

Which is why the changes are erratic rather than gradual. It isn't a dimmer switch being turned down. It's a system misfiring intermittently before it stops.

The bleeding that needs an appointment

Most perimenopausal bleeding changes are just that — changes. But some patterns need looking at, and this is not the section to guess your way through.

Bleeding after you thought you'd finished. This is the clearest one. Postmenopausal bleeding means unexplained vaginal bleeding more than 12 months after your periods stopped. NICE guideline NG12 — the suspected cancer referral guidance, amended in 2026 — says people aged 55 and over with unexplained postmenopausal bleeding that can't be attributed to HRT should be referred on a suspected cancer pathway, and that referral should be considered for those under 55 with the same presentation.

That wording sounds alarming. It's worth being clear about what it means: it means bleeding at that stage always gets investigated, not that it's usually cancer. Most cases turn out to be something else. The point is that nobody can tell which is which without looking, so the system doesn't guess.

Bleeding on HRT that doesn't settle. The NHS advises that some irregular bleeding or spotting when starting HRT should settle within six months, and to talk to your GP if you're still having irregular or heavier bleeding or spotting after that.

Anything that's frightening you or disrupting your life. Very heavy bleeding, bleeding between periods, bleeding after sex. I'm not going to give you a threshold for "too heavy" — there isn't a clean one, and the honest advice is that if you're changing protection hourly, bleeding through at night, or organising your life around it, that's worth a GP appointment regardless of what a website says is typical.

This list isn't exhaustive. Other conditions can cause irregular bleeding, and they don't stop existing because you're in your forties. Perimenopause is a reasonable explanation, not an automatic one.

The thing that catches people out

Irregular periods are not infertile periods.

The NHS is specific about how long contraception is needed: for one year after your final period if you're 50 or over, and for two years after your final period if you're aged 40 to 49. It also notes that the combined pill isn't recommended from age 50, as the risks generally outweigh the benefits, and a GP may suggest progestogen-only contraception instead.

If your cycle has gone haywire and you've quietly concluded the question has answered itself — it hasn't. Worth raising at the same appointment as everything else.

One more thing worth knowing

The NHS notes that ethnic background can affect symptoms of perimenopause and menopause, including how severe they are and how long they last — giving the example that women from a Black ethnic background are more likely to have hot flushes that are severe and continue for longer.

Most menopause content is written as though everyone's experience is the same shape. It isn't, and if yours doesn't match what you're reading, that's worth saying out loud in an appointment rather than assuming you're the outlier.

What actually helps

Write it down. Not obsessively — just dates, rough flow, anything unusual.

Under current UK guidance, for women over 45, perimenopause is identified from symptoms and cycle changes rather than from a blood test. Which means the record of what your periods have actually been doing isn't supporting evidence for the diagnosis. It substantially is the diagnosis, and reconstructing eight months of it from memory in a ten-minute appointment is a bad way to do it.

Three months of notes changes that conversation entirely.