Irregular periods can be difficult to deal with because, as the name suggests, they’re often unpredictable. Whether you’re the kind of person who likes to plan for everything or you prefer to take things as they come, irregular periods can be stressful and might leave you feeling like you’re not in control.

What is considered an irregular period?

When we talk about irregular periods, what we’re actually referring to is when the length of your menstrual cycle varies. This is the time between the first day of one period and the first day of your next period. For example, it may be 23 days one month, then 33 days the next. This can make it hard to track your period and know when your next one will come. It can also make it more difficult to identify key events in your cycle such as ovulation. Lots of people have irregular periods, however you should speak to a GP about yours if:

  • You’re under 45 and your periods suddenly become irregular
  • You get periods more often than every 21 days
  • You get periods less often than every 35 days
  • There’s a difference of more than 20 days between your shortest and longest cycles
  • If your periods last longer than 1 week

Additionally, irregular periods may include a variable heaviness of flow during the menstrual phase. Generally speaking, this should be compared on a month-on-month basis, rather than day-on-day. Many people find their flow gets lighter as they get closer to the end of their period - this is perfectly normal. However, it may be a cause for concern if one period is significantly heavier or lighter than the next.

Comparing yourself to your peers isn’t always the best way to determine whether or not your period is irregular. Different people have different cycle lengths, and both short and long cycles can be perfectly normal. It’s generally a good idea to get a feel for what is normal for you, and then if you do experience any unexpected irregularity, you’re more likely to notice it and can get medical advice if necessary.


What causes irregular periods?

There are lots of factors that could potentially cause or contribute to irregular bleeding, which can make it hard to tell what is causing yours. One thing that may help is keeping a symptoms diary to see if you can spot any patterns in your periods. This may help you or a medical professional to discover the cause of your irregular periods.


For the first few years after you enter puberty and start menstruating, your periods may be irregular. This is a side effect of your body adjusting to new levels of hormones in your blood. Levels of oestrogen and progesterone can fluctuate for up to two years, causing irregular periods during that time.

Early pregnancy

A late period is a classic sign of pregnancy. In some cases, you might experience light period-like bleeds during the early stages of pregnancy - and it’s easy to assume that this means you’re not pregnant. The best way to rule out pregnancy as a cause of irregularity in your periods is to take a pregnancy test.


Many women find they don’t get periods at all while they are regularly breastfeeding, and any bleeding they do experience may be considered irregular. This isn’t usually a problem, however it’s important to remember that it is still possible to conceive during this time, so contraception may be necessary.


Hormone levels become unstable and can fluctuate in the time leading up to menopause, causing irregular periods. This isn’t usually a cause for concern, but you may wish to discuss it with your GP to see if the symptoms can be eased.

Hormonal contraception

Some types of hormonal contraception may affect the regularity of your periods. You may experience irregular bleeding on the mini pill, the combined pill or the intrauterine system (IUS) amongst others. In some cases, these symptoms ease after a few months of using the contraceptive once your body adjusts. If you experience very frequent, heavy or prolonged bleeding while taking the mini pill, speak to your doctor or pharmacist.  

Physical or mental stress

As well as mental stress, extreme physical changes may have an effect on the regularity of your periods. This includes things such as extreme weight loss or gain, malnutrition, eating disorders or excessive exercising. If you suspect this may be the cause of your irregular periods, you should speak to a GP. They will be able to assess if this is a likely cause and, if necessary, refer you to someone who can help you to tackle the problem and reduce your symptoms.

Medical conditions

In some cases, medical conditions may be responsible for irregular periods. These may include:

  • Polycystic ovary syndrome (PCOS)
  • Endometriosis
  • Pelvic inflammatory disease
  • Thyroid problems
  • Adenomyosis
  • Fibroids

Rarely, irregular periods can be a symptom of cervical cancer or womb cancer. These conditions can cause bleeding in between periods or during sex. If you suspect you might have any of the above conditions, speak to your GP.

Your normal

Finally, your irregular periods may simply be what’s normal for you. Some people naturally have more variation between periods than others - and most people experience some period irregularity at one time or another in their lives. If your periods have only recently started being irregular, that might indicate a different cause, but some people find their periods have been irregular since their very first cycle. This may be something you can manage with medication, or you may be able to simply get used to your varying cycles. If you are concerned about your period, speak to your doctor or pharmacist who will be able to offer help and support.



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