Shop sustainable period care with YourCycle. Ships from NZ.


This section doesn’t currently include any content. Add content to this section using the sidebar.

Image caption appears here

Add your deal, information or promotional text

Irregular cycles: what are they, and why do they happen?

Very few people have their period at the exact time every month. But when do normal variations become irregular cycles? What does it even mean to have “regular cycles”? Let’s talk about it!

Menstrual cycles are considered irregular when the length of time between periods consistently varies and/or falls out of regular ranges. Pregnancy is one of the most obvious causes of a late or missing period, but there are many other reasons a cycle could be irregular. These include stress, lifestyle changes, starting or coming off hormonal birth control, and the beginning of having cycles (menarche), as well as when they begin to stop (perimenopause).

Cycles that are consistently irregular can also impact general health, and can indicate that there’s something affecting your body’s ability to function optimally, such as chronic stress, or an underlying health condition. So if you’re having irregular cycles and you don’t know why, it’s absolutely worth addressing this with your healthcare provider. 

What is a regular cycle?

Regular cycles are cycles that more often than not fall into normal ranges. But what are the normal ranges?

  • Adolescents: 21–45 days
  • Adults: 21–35 days
  • Adults: cycles that vary in length by no more than 7–9 days (for example, if your most recent cycle was 29 days, the next won’t be over 36-38 days or fewer than 20-22 days)
  • Never a gap of more than 90 days between cycles, even if as a one-off (unless otherwise explained by starting/stopping hormonal birth control, recent pregnancy, menopause, or something similar)

What are irregular cycles?

Over a 6-month period, if your cycle doesn’t meet all the criteria of a regular cycle the majority of the time, it’s considered irregular. Missing a period every now and then isn’t necessarily a big deal, but if your periods are consistently unpredictable, or the gap of time between them is particularly long or short, they may very well be clinically irregular.

What causes irregular cycles?

Here are some causes of irregular cycles, by category.

Pregnancy and life stages

  • Being in the first few years after your first period (so don’t stress if your first few years of having periods is inconsistent! This is very common and natural)
  • Perimenopause (the period of time before your periods end)
  • Pregnancy
  • The postpartum period (after a pregnancy)
  • Breastfeeding (your body is still working hard to click back into its regular routines after the baby hormones - don’t worry about this and do your best to look after yourself and baby during this special time)
  • Recurrent miscarriages (whether or not you’re aware of them)

Lifestyle factors/changes

  • Doing shift work or working night shifts
  • Sleep disorders/issues with your body’s natural sleep/wake cycle (circadian rhythm)
  • Jet lag/long-distance travel
  • Chronic stress (if this sounds like it might be you, trust us, your mental health is more important than what you’re stressing about! Please, prioritise that <3 )
  • Intensive exercise
  • Substance use/abuse
  • Quickly losing or gaining weight (usually at a rate faster than +/-0.2–0.9kg per week)
  • Disordered eating (malnutrition, undereating, binge eating, etc.) 
  • Certain medications
  • Starting/stopping hormonal birth control

Medical conditions

  • Polycystic ovarian syndrome (PCOS) or endometriosis
  • Problems with your thyroid 
  • Diabetes
  • Infections of your vagina or reproductive organs (uterus, ovaries etc)
  • Abnormal lumps in the uterus (uterine polyps, fibroids, growths, or non-threatening tumours)
  • Cancer cells (of the cervix, endometrium etc) - this is a rare cause, but obviously warrants exclusion
  • Bleeding disorders (some menstruators have bleeding between periods  - this should be investigated because it can also be a sign of cancer)
  • Other medical conditions

Why should you care about irregular cycles?

Having a regular cycle can help you get pregnant if that’s what you’re trying to do! Even if this might not be you for some time, getting irregular cycles assessed and treated earlier, may prevent fertility issues later on. But most people aren’t actively trying to get pregnant, so here are some reasons to care about having a regular cycle that aren’t related to fertility.

Continually irregular cycles can have a big impact on short- and long-term health. Menstrual cycle health is related to more than just your fertility: it can impact your heart health, metabolism, sleep, mood, as well as being an indicator of underlying medical conditions. This is why it’s important to diagnose irregular cycles as early as possible! A healthy menstrual cycle is a sign of a healthy body.


Cycles that consistently fall out of the expected ranges can be managed. In fact, managing an irregular cycle can help with fertility, as well as long-term and short-term health. If you think you might be having consistently irregular cycles, we recommend seeing your healthcare provider, as they may have ways they can help.

Did you find this article helpful?

Download the YourCycle app for personalised information on everything to do with your cycle. It’s completely free and always will be.


 Post by Miranda Bromage