What Causes Menstrual Cycle To Change Dates? Demystifying Irregular Periods

What Causes Menstrual Cycle To Change Dates? Demystifying Irregular Periods

What Causes Menstrual Cycle To Change Dates? Demystifying Irregular Periods

Every month, 1.8 billion people across the world menstruate - that’s over a quarter of the global population. Despite this, menstrual cycles can still be a source of mystery for many of us. In this blog, we seek to demystify menstrual regularity: what causes it, and what we can do about it.

Irregular Periods

The average menstrual cycle lasts 28 days (although it's normal for it to be a bit shorter or longer than this). A regular cycle is usually established after puberty, but periods can still vary by a few days each time.

Irregular periods may be early or late, and vary in how long they last or how heavy your flow is each month.  

What To Do When Your Period Is Shorter And Lighter Than Usual

Periods aren’t always uniform in their length and flow, but having a shorter and lighter period than usual can be a sign of other factors at play. Some of these may include: 

  • Pregnancy
  • Weight gain or weight loss
  • Stress
  • An overactive thyroid
  • Hormonal birth control
  • Polycystic ovary syndrome (PCOS)
  • Early menopause 

While shorter and lighter periods don’t usually pose a serious health concern, always talk to your doctor if you notice a change in your usual menstrual cycle. 

What Causes Menstrual Cycle To Change Dates?

As above, periods are a very dynamic process, and there are a number of things that can lead to changing menstrual dates. In addition to the reasons already covered, menstrual dates can be affected by physical health, lifestyle factors and mental health.

Physical health

Changes in weight can throw your period regularity off. Storing more fat in your body can affect your hormone balance. Similarly, losing weight can put your body into stress mode, causing a hormonal imbalance which can also impact your periods. 

Lifestyle factors

Smoking, meanwhile, can also be a major culprit for changing period dates. Research has shown that it can shorten your menstrual cycle by an average of 2.6 days.

Mental health

Many of our bodily functions are actually controlled by the brain, not our bodies - and menstruation is no exception. This 2018 study shows that stress can significantly impact your body’s ability to menstruate. This is because an increase in the stress hormone, cortisol, can lead to irregular bleeding or periods stopping altogether. 

3 Treatment Options for Irregular Periods

Hormonal birth control 

Oral contraceptive pills, hormonal patches, vaginal rings, or hormonal intrauterine devices (IUDs) can help regulate menstrual cycles by providing a consistent level of hormones. They can help balance hormone levels and regulate the timing and duration of periods. 

Lifestyle changes

Hormones - and therefore periods - can be better balanced by making certain lifestyle changes. Major ones include maintaining a healthy weight, engaging in regular exercise, managing stress levels, getting enough sleep and adopting a balanced diet rich in fruits, vegetables, whole grains and lean proteins.


Certain medications can promote a healthier hormonal imbalance. For example, medications such as metformin can help manage insulin resistance in women with polycystic ovary syndrome (PCOS), a common cause of hormonal imbalance. 

Hormone-regulating drugs like clomiphene citrate may also be prescribed to stimulate ovulation and regulate menstrual cycles. Speak to your healthcare provider to understand the best course of action for you.


Why did my cycle change from 28 to 31 days?

While the average menstrual cycle is 28 days, it’s normal for this to range from between 25 to 35 days. If you’ve noticed a shift in your usual cycle length, it could be down to a hormonal imbalance, stress, diet, exercise or medications. 

Why did my cycle change from 28 to 35 days?

Doctors consider a person to have irregular periods if their cycles are longer than 38 days, or if the length of each cycle varies by more than 7–9 days. This can be down to a host of different reasons, so it’s best to speak to your health care provider for professional insight. 

Is it normal for your period to change dates?

A change in period dates can be your body’s response to a range of different factors, including weight fluctuations, stress, health conditions or certain types of birth control. It’s usually nothing to worry about, but it’s worth speaking to your health care professional to put your mind at ease.  

Final Thoughts on What Causes Menstrual Cycle To Change Dates

Human bodies - and the hormones we come with - are hugely complex, and it’s common for menstrual cycles to fluctuate in length, flow and regularity throughout our lifetimes. While a slight change doesn’t usually pose any serious health risk, the reason behind it can differ significantly from person to person.

If you’re worried about irregular periods, always speak to a health care professional to gain more clarity on why your cycle may have changed, and what you can do about it.  

Back to blog