Irregular Periods in Your 40s: Why Your Cycle Is Changing

Your period used to be something you barely thought about. For twenty years you knew roughly when it was coming and what it would do. Now it turns up four days early, or eleven days early, or it skips a month and then arrives like it has something to prove. You have checked the back of your jeans in a work bathroom and felt that small cold drop in your stomach.

Irregular periods in your 40s are, most often, the first visible sign of perimenopause. A shifting cycle length is the marker clinicians rely on most to tell that the transition has begun. But most often is not always. Other things that need treating look exactly like this, and a few bleeding patterns need a doctor whatever the cause.

What “irregular” means, and why your cycle is changing

A cycle runs from the first day of one period to the day before the next, and anything from 21 to 35 days is typical. What is new in perimenopause is the size of the swing: not 28, 29, 27, but 26, then 34, then 24, with bleeding that floods one month and barely shows the next. It is the loss of your own pattern, rather than a failure to match a textbook average, that carries the information.

Most women expect the change to mean skipped periods. That comes later. The first move is usually the opposite. As the pool of follicles in your ovaries shrinks with age, the brain signal that recruits one each month rises to compensate, ovulation arrives earlier, and the follicular phase contracts by a few days. A woman who ran a reliable 28 day cycle at 38 may find herself running 25 at 44 with no other symptom at all. It is one of the most overlooked early signs of perimenopause, and the reason so many women say the same baffled thing: my period is fine, it just keeps arriving too soon.

Later, ovulation becomes unreliable, and the cycles where no egg is released can stretch on for weeks before the lining breaks down. That is when the long gaps and the flooding periods begin. None of it is quick. Perimenopause usually starts in the mid-40s, sometimes the late 30s, tends to run four to eight years, and the final period comes at around 51 on average.

The markers clinicians watch, and the test that often fails you

Clinicians stage the transition with a system called STRAW+10. A persistent difference of seven days or more between consecutive cycles marks the early transition, and persistent is the word that matters: one odd month tells you little, and it is the recurring variability that carries the signal. A gap of 60 days or more without a period marks the late transition.

It is also why “my labs came back normal” is such a common experience after 45. Hormone levels swing week to week, so a single panel can catch a good day and tell you very little, while your cycle history cannot be caught on a good day. The pattern, not the panel, is where perimenopause is actually read.

Under 45, blood tests genuinely do matter. Guidelines suggest testing follicle stimulating hormone between 40 and 45 where there are menopausal symptoms, a change in cycle among them. And if you are under 40 and your periods have become erratic or stopped, ask to be assessed for premature ovarian insufficiency. It is treatable, and treatment continues at least to the age of natural menopause, to protect bone and heart health.

One caveat, because it sends women down the wrong road. If you are on hormonal contraception, have a hormonal IUD, have had an endometrial ablation or a hysterectomy, or have PCOS, your bleeding pattern cannot tell you where you are. Cycle staging does not apply to you, and you need a clinician rather than a tracker.

Other causes of irregular periods in your 40s

Honesty serves you better than reassurance here. Pregnancy comes first, because a missed period at 43 is still a missed period. Thyroid disease disturbs cycles and brings fatigue and mood change with it. Iron deficiency, with or without outright anemia, is common alongside heavy bleeding and produces an exhaustion that looks like everything else here. Fibroids, endometrial polyps and adenomyosis all cause heavy or irregular bleeding at exactly this age, and all are treatable, as is endometrial hyperplasia, a thickening of the womb lining. PCOS, raised prolactin, celiac disease, some medications, big weight change, hard training and sustained stress each shift a cycle, and depression can hollow out your energy independently of it all.

Most of this is settled with a conversation, an examination and a few tests. Ask for thyroid function, a full blood count with ferritin rather than hemoglobin alone, a pregnancy test where relevant, a pelvic ultrasound, and a biopsy of the womb lining if your bleeding warrants one.

When to see a doctor

Perimenopausal cycle change is common and usually benign. The patterns below are different, and they are not ones to watch and wait on.

• Bleeding between periods, or bleeding after sex. Both need assessment, even if it is light, even if it stops. Bleeding after sex needs someone to look at your cervix rather than a phone call, and your cervical screening brought up to date.
• Any bleeding at all after twelve months without a period. Even one spot, even once. Where it cannot be put down to hormone therapy, NICE treats it as a suspected cancer pathway referral. Bleeding on HRT still needs looking at, it just follows a different route. Ask to be seen.
• Very heavy bleeding. Soaking a pad or tampon every hour for several hours, clots larger than a quarter, or bleeding that keeps you at home. If you are soaking a pad an hour and feel dizzy, faint or breathless, or have palpitations or chest pain, that is same-day emergency care, not a booking.
• A missed or unusually late period. If there is any chance of pregnancy, take a test, however unlikely it feels. A late period with one-sided pelvic pain, shoulder tip pain, dizziness or fainting could be an ectopic pregnancy, and that needs emergency assessment the same day.
• Cycles consistently shorter than 21 days, or periods lasting longer than seven days. Drifting from 28 days to 25 is the ordinary story of this decade. Settling below 21, or bleeding that runs past a week, is a different thing and needs looking at.
• Persistent bloating, feeling full quickly, loss of appetite, new pelvic pain, unexplained weight loss. Vague symptoms, which is exactly why ovarian cancer gets missed. If they are new to you and they persist for a few weeks, say so plainly.

Most of these turn out to have an ordinary, treatable cause. Some do not. Bleeding after the menopause and bleeding after sex are the way cancers of the womb lining and the cervix first announce themselves, and both are highly treatable when they are caught early. That is the whole reason this list exists. The threshold for investigating the lining is lower if you have a raised BMI, PCOS or diabetes, if you take tamoxifen, if you have never been pregnant, or if womb or bowel cancer runs in your family. Say those things out loud at the appointment.

What can be done about it

None of this is something to endure simply because it is normal for your age. Tranexamic acid and anti-inflammatories such as mefenamic acid are taken only on bleeding days and can reduce a heavy flow. Cyclical progestogens can steady an erratic pattern. The hormonal IUD thins the womb lining, often lightens or stops bleeding, provides contraception and protects the lining if estrogen is added later, which is why it does so much work at this age. The combined pill, where nothing in your history rules it out, controls the cycle and provides contraception at once. Menopausal hormone therapy is an option for the wider cluster of symptoms, hot flashes and sleep and mood among them, with real benefits and real trade-offs that depend on your history.

One thing catches many women out, so it is worth saying plainly. Menopausal hormone therapy is not a contraceptive. If you take it and still need contraception, you need contraception as well, because erratic cycles do not mean you have stopped ovulating. Contraception is generally advised until twelve months after your last period if you are over 50, and two years if you are under 50, and it can usually stop at 55 whatever your bleeding is doing.

What you can do tomorrow

Write it down. Not perfectly, and not forever. Just the first day of every period, how long it lasted, how heavy it was, and anything that surprised you. Within three or four cycles the shape appears: whether your cycles are shortening, whether the difference between them is widening past that seven day mark, whether the broken sleep and the flat mood land in the same week every time.

That record turns “I feel off and I do not know why” into a sentence a doctor can act on. My cycles have gone from 28 days to anywhere between 23 and 34 over six months, and I bleed heavily for six days. That is much harder to wave away. Tracking your symptoms is not about optimizing yourself. It is about being believed, starting with by yourself. If it helps to see the whole cluster before your appointment, the perimenopause self assessment takes four minutes and scores itself in your browser. It is preparation for a doctor, never a substitute for one.

Your cycle is not betraying you. It is telling you something, in the only language it has, and you are allowed to write it down and take it seriously.

This article is for educational purposes and is not medical advice. Bleeding between periods, bleeding after sex, any bleeding after twelve months without a period, a late period that could be a pregnancy, or heavy bleeding with dizziness or faintness all need prompt assessment by a clinician rather than watching and waiting.