How many days are there between periods?

The menstrual cycle lasts from a person’s first day to the day before the next period comes in. In some extent, it’s common in vary the duration of someone’s period from month to month.

The Office on Women’s Health (OWH) says the menstrual cycle lasts 28 days on average. However, a report conducted in 2019 found that the average duration of the cycle is a little over 29 days.

In this article , we’ll look at what a normal period is, the causes of a long or short cycle and how somebody can track their cycle’s regularity.

What is normal?

A lady checking her period with mobile app
A person can try tracking their periods using a mobile application.

Every month, the uterine lining thickens to prepare for pregnancy. When there is no implant of a fertilized egg in the uterus, the uterine lining sheds, triggering a period. The period is the first part of the life of a person, and marks the end of the previous cycle.

Varying in the number of days between the periods is usual. Anywhere from 24–38 days could be a normal range. Doctors can call a cycle falling infrequently outside of this time frame. Doctors can also consider an abnormal period, if it varies in length from month to month by more than 20 days.

Cycle variation doesn’t necessarily signify any problem, though.

Causes

There are many possible explanations why an person can encounter an unusual amount of days between periods.

A 2019 study that evaluated more than 600,000 menstrual cycles found that the most important factor deciding the duration of the cycle is the amount of time a person takes to ovulate. Ovulation comes when an egg is released from the ovaries. The average individual ovulates after their last day, around 16 days.

If someone is ovulating early, their duration may be shorter. The cycle may be longer if they ovule later. How much a person ovulates can change according to various factors, including:

  • Age: Adolescents may not ovulate regularly to begin with, so the length of their cycles can fluctuate. Similarly, people entering menopause will start to ovulate less often, causing changes to period and cycle length.
  • Stress: A 2013 study of shift workers found that menstrual cycle disorder was more common in people who had stressful jobs and irregular working hours.
  • Energy levels: Intense exercise and eating disorders, such as anorexia nervosa or bulimia, can mean a person stops ovulating, causing irregular periods.

According to an older article in the Journal of Clinical Endocrinology & Metabolism, both long and short cycles can mean that during this period a person did not ovulate.

Causes of a short cycle

Women who ovulate in their cycle earlier also have fewer days between the periods. Some common short-cycle causes include:

  • Endometriosis: A meta-analysis found that cycles shorter than 27 days correlate with a higher incidence of endometriosis. Symptoms of endometriosis include severe menstrual cramps, long periods, and heavy bleeding.
  • Luteal phase defect (LPD): The luteal phase is the second half of the menstrual cycle. According to Resolve, some doctors believe that an LPD could cause a short luteal phase, making it difficult for a fertilized egg to implant in the womb lining. However, there is some debate among experts about whether LPD exists.
  • High body mass index (BMI): In one study, women with a high BMI were more likely to have a short luteal phase, and 34% less likely to get a positive result when researchers tested if they had ovulated.
  • Birth control: Sometimes, a person using hormonal birth control will experience “breakthrough bleeding.” This type of bleeding is not a true period, but rather a side effect of the birth control.

Causes of a long cycle

The later any individual ovulates into their cycle, the later that will be their period. A long cycle could mean a person ovulating very late, or not ovulating at all.

Relevant reasons for a long menstrual cycle according to the OWH include:

  • Polycystic ovary syndrome (PCOS): Sometimes, late ovulation is a sign of PCOS. Other symptoms of PCOS include irregular periods, unusual or excessive body hair growth, unexplained weight gain, and insulin resistance.
  • Hyperthyroidism: When the thyroid gland produces too much thyroid hormone, it can cause late or missed periods. The OWH list other hyperthyroidism symptoms as feelings of nervousness, unexplained weight loss, a rapid heartbeat, and trouble sleeping.

A person who has these symptoms should talk to their doctor. If a person has not had their period, they should also accept the possibility that they may be pregnant.

How to track your period 

Tracking periods can help a person predict their next period. It can also help an individual determine if their cycle is regular or irregular.

An individual may monitor their cycles in a few ways, like mobile apps, or in a diary or calendar.

Some people use period monitoring as well to control when they can ovulate. According to an article in npj Digital Medicine, however, period tracking alone is not accurate, because ovulation day can vary from month to month. In addition, a typical duration of the cycle doesn’t necessarily mean a person ovulated.

In a Bioengineering and Translational Medicine report, if a person wants to find out when they ovulate, they should also monitor:

  • Cervical fluid: The cervical fluid that comes out of the vagina changes during a person’s cycle. When a person is most fertile, the fluid tends to be more abundant and watery and may resemble egg whites.
  • Basal body temperature: Recording body temperature each morning can help confirm ovulation. When the temperature rises for several days and remains elevated, this may mean a person has ovulated. This method is most effective if a person takes their temperature at the same time each day before moving around.
  • Ovulation tests: Ovulation tests measure for surges of luteinizing hormone. A positive test means a person may be about to ovulate. However, some disorders can cause hormone surges even when a person does not ovulate.

How irregular periods affect fertility

Because sometimes an irregular period means a person is not ovulating, very long or short cycles could be a sign of a hormonal imbalance that can make it hard to conceive.

It’s not always the case, however, that someone with irregular periods won’t get pregnant, or that somebody with normal periods will. The OWH lists the different causes of male and female infertility.

When to see a doctor

People with irregular cycles who want to become pregnant may want to see a doctor before attempting to conceive.

People should also notify a doctor if they encounter abrupt changes in their cycle or whether they have underlying symptoms such as severe cramps or heavy periods.

Summary

In between periods the total number of days is 28–29. It is also normal for the cycles of peoples to differ from month to month. A significant amount of variation could be a sign of an underlying condition or a hormonal imbalance.

If a person has concerns about the number of days or their fertility between periods, they should contact a doctor.

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