Menstrual Cycle


May 16, 2023

What is an irregular period?

Find the answers to your questions about irregular periods: what it means, causes, and when to see a doctor

If you’ve ever found yourself wondering “what is a normal period cycle?” or “why is my period irregular?” then this is the article for you. We all worry about our bodies doing something different to other people’s, but these differences are much more common than you think.

What you need to know about irregular periods

  • “Irregular” might sound scary but it’s just the word used to describe situations that fall outside the range that doctors generally look for. It does not mean there’s anything irregular or abnormal about you!
  • The main thing to look for is what is irregular for you.
  • 14-25% of people have irregular menstrual cycles, so it’s not as uncommon as you’d think.
  • Your cycle might be more or less regular at different times in your life.

What does having an “irregular” period actually mean?

The menstrual cycle is the natural process that prepares your body for the possibility of pregnancy, lasting from the first day of one period to the day before the next.

For most people, the cycle lasts between 21 and 40 days, so if it’s longer or shorter than this, then that’s what healthcare professionals call irregular.

I think I have an irregular cycle, should I be worried?

Not necessarily!

Of course, it is important to talk to a healthcare professional about your menstrual health, especially if you’re concerned. But you should also remember that everyone is different and one of the most important measures is actually to see what’s regular for you.

For example, if your periods consistently happen every 42 days, then that’s probably not an issue (though still double check with your doctor if you haven’t already).

PLUS, some variation is totally normal throughout your lifetime, and we’ll look at situations where it can happen lower down.

The main thing to look out for is if your cycle suddenly changes, as it could be an early sign of some other problem.

Why might my cycle be irregular?

Your menstrual cycle involves a complicated mixture of hormones, so disruption of these due to stress, illness or treatments can play a factor. Let’s look at the most common reasons for an irregular period.

It’s the first few years

During the first few years of your period, the gap between them can vary more: between 21 and 45 days, although this gap usually shrinks in the third year.


If you’re pregnant then you won’t have a period!

After pregnancy

It can take a while for your period to resume after giving birth, and this can be even longer if you’re breastfeeding. In some cases, it can take up to 6 months, although 2-3 months is more common.

You’re nearing menopause

The few years before menopause - a stage known as perimenopause, usually after 45 - can cause your cycle length to become much more varied, from as little as 14 days to up to 50 days.

Some contraceptives

Certain types of contraceptives work by affecting your hormone levels, like an IUD or the contraceptive pill. When you start or stop these methods, the change in your hormones can disrupt your normal cycle.

You’re stressed, tired, overworked, travelling, or have gained/lost weight

Yeah, there are quite a lot of things that can affect the regularity of your menstrual cycle. Rapid weight gain or loss, being stressed, travelling long distance, being very tired - all these can have an impact.


Some illnesses, including thyroid problems, can cause disruption.

When to see your doctor

So, if there are all these reasons for irregular periods, when should you see a doctor?

  • Your period stops or the gap between periods suddenly changes
  • Your periods happen less than every 24 days or more than every 38 days - just to be sure!
  • The gaps between your periods vary by more than 7 days each time (so maybe 28 days one month, then 36 the next)

What next?

If you’ve got more questions about the menstrual cycle, read our quickstart guide to learn more.

Find out how tracking your period can help you, whether that’s with getting pregnant or just day to day.

Late period got you panicking? Here’s all you need to know in our blog about late periods.

And remember to sign up to the Mihna newsletter for more advice, stories and information about menstrual health, pregnancy, sex and more.