1. Your cycle
  2. Health
  3. Period

Flo Fact-Checking Standards

Every piece of content at Flo Health adheres to the highest editorial standards for language, style, and medical accuracy. To learn what we do to deliver the best health and lifestyle insights to you, check out our content review principles.

How Late Can a Period Be Before You Should Worry? 8 Reasons for a Delayed Period

It’s normal to feel some concern when a period doesn’t come when it’s expected. Let’s take a closer look at the several possible reasons for such a delay.

Average cycle length 

It’s normal for periods to vary a little in length from month to month. How late can a period be before you should worry? Generally, a period is considered late if it’s more than five days past due. 

Although a missed period can be confusing, having an understanding of the menstrual cycle and the body can help clarify this situation. Here’s how the menstrual cycle works.

Take a quiz. Find out what you can do with our Health Assistant

Each menstrual cycle begins on the first day of your period and continues until the next period begins. The average menstrual cycle is about 28 days long, but a healthy cycle can be anywhere from 21 to 35 days long. A period that starts between one and four days earlier or later than expected is considered normal. 

Most periods last between three and five days, but a period anywhere between three and seven  days long is also considered normal. A period that happens anytime of the month and is very unpredictable is considered irregular.

Reasons for a late period

Now that we’ve explained what qualifies as a regular menstrual cycle, let’s go over why some people have late or irregular periods. 

During the early stages of puberty, it’s common to have irregular cycles. It’s normal for adolescents to have irregular cycles for the first three years after they get their period. This is because the ovaries may not be releasing an egg every month yet, since hormone levels are still changing. However, for people who are already past that phase, there are lots of other things that can cause a late period and irregular periods.

Here are eight common causes of a late period: 

1. Stress

Stress may be one of the most common reasons for a late period. There are many types of stress, including:

  • Emotional stress caused by relationship problems, depression, or anxiety
  • Physical stress caused by surgery, injury, or illness such as viral or bacterial infections, diabetes, or inflammatory diseases of the gastrointestinal tract

Some stress is a regular part of life. However, too much of it can disrupt the body’s hormonal balance, which may result in a late or missed period. 

The menstrual cycle is regulated by a complex system that includes brain structures (the hypothalamus and pituitary glands), the thyroid gland, the ovaries, and the uterus. Stress can interfere with the body’s cycle regulation by affecting the hypothalamus. When it does, the body can turn on its defense mechanisms and focus only on vital processes, postponing the next period until the situation improves. Usually, once the stress level is reduced, menstruation is restored. If this doesn’t happen, it may be better to consult a health care provider. 

Proper stress management can be very helpful and includes things like meditation and exercise.

2. Weight loss

Weight fluctuation is another common reason for a late or missed period. Being underweight can also prevent a person from getting their period. 

Rapid weight loss due to dieting or excessive exercise can also affect the body’s hormones. The body needs time to recover after losing weight in a short amount of time. Staying healthy and maintaining an active lifestyle can help menstrual cycles become regular again.

3. Excess weight

Excess weight can affect ovulation by altering the body’s levels of estrogen and progesterone. This can cause irregular periods.

4. Birth control

Starting or stopping taking hormonal birth control can also cause changes to the menstrual cycle. Birth control pills contain the hormones estrogen and progestin. These hormones prevent the ovaries from releasing eggs and significantly reduce the odds of becoming pregnant. They can also reduce the frequency of periods. For some people, it may take up to three months before their cycle goes back to normal after they stop using hormonal birth control.

5. Polycystic ovary syndrome (PCOS)

PCOS is a fairly common condition that causes irregular periods. This condition causes the body to produce a higher amount of androgen. It also causes small cysts to form on the ovaries when follicles don’t rupture to release eggs. In addition to irregular periods, common symptoms of polycystic ovary syndrome include: 

  • Excess facial hair growth (hirsutism)
  • Infertility
  • Weight gain
  • Acne and oily skin
  • Male pattern baldness

If any of these symptoms are present in addition to late or irregular periods, a health care provider can perform tests to make a diagnosis and recommend treatment.

6. Pregnancy

Pregnancy is another common cause of late periods. If a period is more than a week late, following unprotected sex anytime since the last period started, there’s a chance of pregnancy. Home pregnancy tests can typically determine pregnancy starting on the first day of a late period. Blood tests detect human chorionic gonadotropin (hCG) in the blood and can be done before the period is late. This test is performed by a health care provider.

7. Early perimenopause

Menopause usually starts between the ages of 45 and 55. There are, however, some people who begin perimenopause early, experiencing signs and symptoms at 40 and sometimes younger. This means that menopause is approaching and ovulation will no longer be regular. People in perimenopause might still ovulate irregularly. 

8. Thyroid disease

The thyroid helps control the menstrual cycle, and a thyroid hormone imbalance may result in a disrupted menstrual cycle. When thyroid hormone levels are too low or too high, it can cause prolonged menstrual bleeding, anovulatory cycles (cycles without ovulation), and irregular periods.

In some cases, thyroid disease can also cause periods to stop for several months, which is called amenorrhea. 

To treat thyroid disease, health care providers may prescribe thyroid hormone replacement for hypothyroidism and thyroid suppression for hyperthyroidism.

When is it time to see a health care provider?

A pregnancy test can confirm pregnancy starting from the first day of a missed period. If any of the following symptoms are present, it’s important to see a health care provider:

  • Unexpected heavy bleeding
  • Severe pain
  • Vomiting and nausea
  • Dizziness
  • High fever
  • Pressure in the lower abdomen

Everybody has different cycles, which can vary in length from month to month. If you have any concerns about your symptoms, a health care provider can answer questions, offer advice, and diagnose and treat any underlying issues. Flo is also a great tool for period tracking, symptom logging, and cycle prediction.

“Menstrual Cycle: What's Normal, What's Not.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 13 June 2019, www.mayoclinic.org/healthy-lifestyle/womens-health/in-depth/menstrual-cycle/art-20047186.

Munro, Malcolm G., et al. “OBGYN.” Obstetrics and Gynecology, John Wiley & Sons, Ltd, 10 Oct. 2018, obgyn.onlinelibrary.wiley.com/doi/full/10.1002/ijgo.12666.

G;, Doufas AG;Mastorakos. “The Hypothalamic-Pituitary-Thyroid Axis and the Female Reproductive System.” Annals of the New York Academy of Sciences, U.S. National Library of Medicine, pubmed.ncbi.nlm.nih.gov/10818393/.

Jacobson, Melanie H, et al. “Thyroid Hormones and Menstrual Cycle Function in a Longitudinal Cohort of Premenopausal Women.” Paediatric and Perinatal Epidemiology, U.S. National Library of Medicine, May 2018, www.ncbi.nlm.nih.gov/pmc/articles/PMC5980701/.

“Polycystic Ovary Syndrome (PCOS).” ACOG, June 2020, www.acog.org/patient-resources/faqs/gynecologic-problems/polycystic-ovary-syndrome.

Skarulis, Monica С., and Brendan С. Stack. “Thyroid Disease.” Womenshealth.gov, 1 Apr. 2019, www.womenshealth.gov/a-z-topics/thyroid-disease.

“When Will My Periods Come Back after I Stop Taking the Pill? Your contraception guide” NHS Choices, NHS, www.nhs.uk/conditions/contraception/when-periods-after-stopping-pill/.

Read this next