Why is my period late? 15 reasons besides pregnancy

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Written by: Pedro Pinheiro, MD

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Estimated reading time for the article: 4 minutos


A late period is often the first sign of pregnancy, but many other factors can contribute to a late or missed period.

Generally, a short delay in menstruation can occur even in women with a regular menstrual cycle and may not have any clinical significance.

In non-pregnant women, even when menstruation doesn’t come in a given month, the chance of it being something significant is small. Stress, miscalculations, changes in contraceptive methods, urinary tract infections and other less relevant situations are usually the most common causes.

Nonetheless, if menstruation is absent for three consecutive months, this is called amenorrhea. In such cases, once pregnancy is ruled out, certain medical conditions may be responsible for the cessation of menstruation.

Main Reasons

This article explores 15 common reasons for delayed menstruation. They include:

  • Pregnancy.
  • Stress and anxiety.
  • Discontinuation of birth control pills.
  • Infections or illnesses.
  • Miscalculations.
  • Recent changes in body weight.
  • Obesity.
  • Excessive thinness or eating disorders.
  • Overexertion through physical activity.
  • Thyroid problems.
  • Breastfeeding.
  • Polycystic ovary syndrome (PCOS).
  • Menopause.
  • Recent onset of the menstrual cycle.
  • Amenorrhea.

If your period is missing, evaluate which of these situations may apply to you.

Primary Causes of Delayed Menstruation


Every sexually active woman who experiences a late period should first consider the possibility of pregnancy. Pregnancy should be the initial hypothesis to be ruled out, even for women who report using contraceptive methods such as condoms or birth control pills.

The cessation of menstruation is typically the earliest sign of pregnancy. However, since about one-third of pregnant women experience light spotting during the first trimester, many might assume their period is arriving as usual.

Therefore, if your period is delayed by a few days, and you subsequently notice vaginal bleeding different from your regular menstrual flow, pregnancy could be the cause.

Don’t wait for symptoms like nausea, breast enlargement, food cravings, abdominal pain, or increased urinary frequency to arise before suspecting pregnancy. A delayed period usually occurs around 3 or 4 weeks into pregnancy, while other symptoms tend to appear after the 4th or 5th week.

There is no more reliable method to confirm or rule out an ongoing pregnancy than taking a pregnancy test. Current tests can detect pregnancy with just one day of menstrual delay. However, tests are more reliable when performed after a week of delay. Blood hCG levels provide the most reliable results. Still, over-the-counter pregnancy tests are easier to use and also offer a high degree of accuracy.

Stress and Anxiety

The menstrual cycle can be significantly influenced by factors beyond the reproductive system. Emotional factors alone can delay your period by a few days. Excessive stress or anxiety can adversely affect hormonal production, regulated by the hypothalamus, a part of the brain. Stress may even prevent ovulation in a particular cycle, leading to a missed period that month.

Stress encompasses various common situations that many people face, such as excessive workload, professional, financial, or family issues, an upcoming important exam, defending a thesis, caring for a sick child at home, and more. Abrupt changes in work schedules, such as the continuous need to work overnight, can disrupt sleep patterns and interfere with the normal ovulatory cycle.

If you are not currently planning for pregnancy and something unexpected occurs during one of your sexual encounters, like a condom breaking or forgetting to take birth control correctly, the stress generated by the risk of pregnancy may also be substantial enough to cause a delayed period.

This process can potentially snowball, as anxiety leads to a late period, which, in turn, triggers even more stress. In such cases, if your period is already 2 or 3 days late, it is best to take a pregnancy test as soon as possible to break this cycle of worry.

Discontinuation of Birth Control Pills 

Women who take oral contraceptives as prescribed usually experience regular menstruation. However, if you choose to discontinue the pill after several years of use, your natural cycle may take some time to regain its normal rhythm.

Amenorrhea, or the absence of menstruation, can occur in some women who stop using birth control, causing them to go months without ovulating. Rest assured, menstruation will eventually resume without any risk of infertility. Patience is vital, as the ovulatory cycle will naturally reestablish itself within 3 to 6 months.

It is important to emphasize that any woman experiencing an absence of menstruation for more than three months should consult her gynecologist.

Post-contraceptive amenorrhea can occur with all forms of birth control, including implants, injections, or pills.

Infections or Illnesses 

Being unwell can lead to delayed menstruation. The illness doesn’t need to be severe, such as a heart attack, tuberculosis, or hepatitis. Common viral infections like the flu or less severe infections such as cystitis or tonsillitis can be enough to disrupt your menstrual cycle, delaying your period by a few days.

Some medications can also impact the hormonal cycle, leading to irregular menstruation. Among the most common are:

  • Antipsychotics.
  • Corticosteroids.
  • Antidepressants.
  • Chemotherapy.
  • Immunosuppressants.
  • Antihypertensives.

Note: Generally, the use of antibiotics does not cause delayed menstruation. Usually, the infection for which the antibiotic was prescribed interferes with the menstrual cycle.


Women with irregular menstrual cycles might face challenges in predicting the exact date of their next period. You might think your period is late when, in reality, it might arrive 2 or 3 days later.

Even women with regular cycles can occasionally experience a minor delay in their period without apparent reason. Your uterus doesn’t adhere to a fixed calendar and isn’t obligated to act like clockwork each month.

Recent Changes in Body Weight

Experiencing significant weight gain or loss in a short period can disrupt the menstrual cycle. Fat cells contribute to estrogen production, the female hormone responsible for egg maturation. Sudden fluctuations in body fat can impact estrogen levels, potentially affecting ovulation and the timing of menstruation.


This factor is a variation of the situation above. Overweight women have an increased mass of fatty tissue, leading to excessive estrogen production. While estrogen is necessary for ovulation, an overabundance of it can inhibit egg release, causing anovulatory periods. Without ovulation, a woman does not menstruate.

Excessive Leanness or Eating Disorders

Another variation of the previous cause, insufficient fatty tissue can also negatively affect the ovulatory cycle by reducing the female body’s ability to produce estrogen. Women suffering from anorexia or engaging in extreme diets typically do not ovulate every month, resulting in not only delayed menstruation but also an increased risk of amenorrhea.

Excessive Physical Activity

Women involved in professional-level sports or physical exercise often experience menstrual irregularities. This applies to triathletes, marathon runners, competitive swimmers, gymnasts, and other professional athletes, rather than women who regularly visit the gym. Factors such as high caloric expenditure, intense training stress, and low body fat levels contribute to these menstrual cycle alterations.

Thyroid Issues

An underactive thyroid (hypothyroidism) or overactive thyroid (hyperthyroidism) can disrupt the menstrual cycle. Uncontrolled thyroid issues generally result in amenorrhea. However, even in milder cases or those treated with thyroid medication, minor fluctuations in blood thyroid hormone levels can cause irregular cycles and menstrual delays.


After giving birth, breastfeeding mothers should not expect their period to return for several months. Breastfeeding causes transient amenorrhea, as the hormones responsible for milk production inhibit the resumption of ovulation. Typically, menstruation resumes when the weaning process begins.

Polycystic Ovary Syndrome

Women with polycystic ovary syndrome often face irregular menstruation due to excessive production of androgens (male hormones). Menstrual delays and the absence of menstruation in a given month are common. Additionally, women with this syndrome tend to gain excess weight, which contributes to menstrual irregularities.


Menopause generally occurs between the ages of 45 and 55. However, some women may experience menopause before the age of 45. There are also cases of early menopause occurring before 40.

Impending ovarian failure is often marked by irregular menstrual cycles and an absence of ovulation in certain months. If you are over 35 and your periods become increasingly irregular, consult your gynecologist.

Recent Onset of Menstrual Cycle

For young women who have recently experienced menarche (first menstruation), it is normal for the menstrual cycle to be irregular during the first few years. Menstrual changes can continue for up to two years after menstruation begins, as the female reproductive system matures. Consequently, menstrual delays are common during this phase.


There are various causes of amenorrhea, including uterine, ovarian, and even brain gland issues that control the production of sexual hormones, such as the pituitary and hypothalamus.

Amenorrhea is different from a menstrual delay. If you have not menstruated for three or more months, this can no longer be considered a delay. While some causes of amenorrhea have been mentioned in this text, numerous others exist.

If you are not pregnant and your menstruation has stopped, consult your gynecologist, as an underlying condition may be inhibiting your ability to ovulate.



Pedro Pinheiro holds a medical degree from the Federal University of Rio de Janeiro (UFRJ) and is a specialist in Internal Medicine and Nephrology, certified by the State University of Rio de Janeiro (UERJ) and the Brazilian Society of Nephrology (SBN). He is currently based in Lisbon, Portugal, with his credentials recognized by the University of Porto and the Portuguese Nephrology Specialty College.

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2 responses to “Why is my period late? 15 reasons besides pregnancy”

  1. Bianca
    Is it common for menstrual irregularities to occur during adolescence?
    1. Dr. Pedro Pinheiro Avatar
      Dr. Pedro Pinheiro
      Yes, it’s pretty common for menstrual irregularities to occur during adolescence, as the body is still adjusting to the new hormonal environment.