Following puberty, most people find that their menstrual cycle settles into a consistent monthly pattern. But what if your period arrives much earlier or later than normal? Or not at all?  

If you’ve had a sudden change in menstrual cycle length, don’t panic. Irregular periods  are fairly common. They can happen for all sorts of reasons – some are nothing to worry about, while others may need medical attention.  

We spoke to Dr Andrea Huddleston to help us uncover the common causes of irregular periods and bring you some tips for managing a change in your cycle. We’ll also explain when to hit up your doctor for guidance.

Everyone’s cycle is unique. Ideally, yours will find its own predictable pattern once you’ve reached adulthood. But if you’ve been asking yourself, why does my period change date every month, you’re not alone. Periods usually happen every 28 days, but that’s just an average – many people’s cycles are a little shorter or longer than the norm.  

“During puberty and in the first couple of years after, it’s fairly normal to have some sort of irregularity,” Dr Andrea says. “But after that, I expect most women’s cycles to be somewhere between 26 to 32 days fairly consistently.”  

However, just because you can’t pinpoint the exact day of your next period doesn’t mean your cycle isn't ‘regular’. It’s normal to get some slight variations in cycle length.   

“It is very common for people to have one or two cycles per calendar year that might blow out a little bit,” Dr Andrea says. “They may become a little bit shorter or longer than what is considered normal for them. There’s lots of things that can cause that.”  

From disruptions in routine to underlying health conditions, there are many potential reasons for a change in your cycle.  

If you feel stressed a lot of the time, you might have your answer. According to Dr Andrea, excess stress can dramatically affect our bleeding pattern.  

“When we’re stressed, we produce a hormone called cortisol, which puts us into a fight-or-flight state,” she says.  

“Cortisol takes priority over all of our other reproductive hormones that regulate our menstrual cycle. So when we need more cortisol, the first thing our body will do is actually start to rob us of our sex hormones – progesterone in particular.”  

Progesterone is the hormone that’s responsible for the smooth running of the menstrual cycle’s luteal phase.  

“Stress can make our periods shorter and even cause a person to skip a menstrual cycle,” Dr Andrea says. “It can stop ovulation and other menstrual cycle functions as well.”  

So if your most recent period only lasted 3 days, but you usually bleed for 5, excess stress could be to blame.  

Other possible reasons for a sudden change in menstrual cycle length may be:  

• Rapid weight gain or loss – Sudden fluctuations in weight and dramatic dietary changes can cause hormonal imbalance and nutrient deficiency, both of which can affect your cycle.  
• Over-exercising – Working out too much can cause your cycle to change. Your metabolism may slow down so much that your body stops ovulating as a way to save energy, leading to the loss of periods altogether.  
• Medications – Many medications can affect your cycle, including aspirin (which can increase bleeding), steroids, antidepressants and emergency contraception.  
• Health conditions – Conditions that may affect hormones, such as polycystic ovary syndrome (PCOS) and thyroid or pituitary gland disorders, can lead to missed periods. Other conditions that may change your cycle include endometriosis, pelvic inflammatory disease and blood clotting disorders.  
• Illness – Viral infections such as the flu can put stress on the body. If you get sick, your body might delay your cycle until you recover.  
• Perimenopause – If you’re over 40 and noticing a change in your cycle, it could be due to perimenopause, the transitional time before menopause. During perimenopause, your estrogen levels start to drop, which can lead to unpredictable periods.  
• Hormonal birth control – Stopping or starting hormonal contraception can mess with your bleeding pattern. For example, the contraceptive implant Implanon slowly releases progestogen into your body to stop your ovarian cycle. This often leads to lighter bleeding or none at all.  
• Sleep deprivation – Studies suggest that a lack of quality shut-eye can throw our cycles out of sync. This means that things like night shift work and travelling across time zones can result in irregular periods.  
• Pregnancy – When you get pregnant, your body releases hormones that prevent ovulation, so your period will stop too. Complications such as miscarriage or an ectopic pregnancy (when a fertilised egg implants outside of the uterus) can also cause unusual bleeding.