If you don’t have any known condition affecting your menstrual cycle, your period should start within 30 days of the start of your last period.

A period is officially considered late if it’s been more than 30 days since the start of your last period. After six weeks without bleeding, you can consider your late period a missed period.

Several things can delay your period, from basic lifestyle changes to chronic health conditions. Here’s a look at 10 potential culprits.

Your body’s stress-response system is rooted in a part of your brain called the hypothalamus. While you may no longer be running from predators, your body is still hardwired to react as if you were.

When your stress level peaks, your brain tells your endocrine system to flood your body with hormones that switch on your fight-or-flight mode. These hormones suppress functions that aren’t essential to escaping an imminent threat, including those of your reproductive system.

If you’re under a lot of stress, your body can stay in fight-or-flight mode, which can make you temporarily stop ovulating. This lack of ovulation, in turn, can delay your period.

Severe changes in body weight can screw with your period’s timing. Extreme increases or decreases in body fat, for example, can lead to a hormonal imbalance that causes your period to come late or stop entirely.

In addition, severe calorie restriction affects the part of your brain that “talks” to your endocrine system, giving instructions for the production of reproductive hormones. When this communication channel is disrupted, hormones can get out of whack.

A strenuous exercise regimen can also cause missed periods. This is most common in those who train for several hours a day. It happens because, whether intentionally or not, you’re burning way more calories than you’re taking in.

When you burn too many calories, your body doesn’t have enough energy to keep all its systems running. This can lead to a hormonal imbalance that throws off your menstrual cycle, leading to missed or late periods.

Periods typically go back to normal as soon as you lessen training intensity or increase your caloric intake.

Polycystic ovary syndrome (PCOS) is a set of symptoms caused by an imbalance of reproductive hormones. People with PCOS don’t ovulate regularly. As a result, your periods may be lighter than normal, arrive at inconsistent times, or disappear altogether.

Other PCOS symptoms can include:

  • excess or course facial and body hair
  • acne on the face and body
  • thinning hair
  • weight gain or trouble losing weight
  • dark patches of skin, often on the neck creases, groin, and underneath breasts
  • skin tags in the armpits or neck
  • infertility

Many love the pill because it makes their periods so regular. But it can sometimes have the opposite effect, especially during the first few months of use.

Similarly, when you stop taking the pill, it can take a few months for your cycle to get back to normal. As your body returns to its baseline hormone levels, you may miss your period for a few months.

If you’re using another hormonal birth control method, including an IUD, implant, or shot, you might completely stop getting your period.

Perimenopause is the time leading up to your menopausal transition. It typically starts in your mid- to late 40s. Perimenopause lasts for several years before your period stops completely.

For many, missed periods are the first sign of perimenopause. You may skip a period one month and be back on track for the following three. Or, you may skip your period three months in a row and find that it arrives unexpectedly, often lighter or heavier than you’re used to.

Early menopause, also known as premature ovarian failure, happens when your ovaries stop working before you turn 40.

When your ovaries aren’t working the way they should, they don’t produce enough estrogen. As estrogen levels drop to all-time lows, you will begin to experience the symptoms of menopause.

Late or missed periods may be an early sign. You may also experience hot flashes, night sweats, and trouble sleeping.

Other signs of premature ovarian failure include:

  • vaginal dryness
  • trouble getting pregnant
  • decreased sexual desire
  • trouble concentrating

Your thyroid is a butterfly-shaped gland in your neck that produces hormones that help regulate many activities in your body, including your menstrual cycle. There are several common thyroid conditions, including hypothyroidism and hyperthyroidism.

Both hypothyroidism and hyperthyroidism can affect your menstrual cycle, causing irregularity, but hyperthyroidism is more likely to cause late or missed periods. Sometimes, your period may disappear for several months.

Other symptoms of a thyroid issue include:

  • heart palpitations
  • appetite changes
  • unexplained weight changes
  • nervousness or anxiety
  • slight hand tremors
  • fatigue
  • changes to your hair
  • trouble sleeping

Certain chronic health problems, especially celiac disease and diabetes, are sometimes associated with menstrual irregularities.

Celiac disease is an autoimmune disease that affects your digestive system. When people with celiac disease eat gluten, their immune system reacts by attacking the lining of the small intestine.

When the small intestine is damaged, it impairs the body’s ability to absorb nutrients from food. Subsequent malnourishment affects normal hormone production and leads to missed periods and other menstrual irregularities.

Those with type 1 and type 2 diabetes might also experience a missed period in rare cases. This tends to only happen when blood sugar levels aren’t managed.

If there’s a chance you may be pregnant and your cycles are typically regular, it may be time to take a pregnancy test. Try to do this about one week after your period was supposed to start. Taking a test too early can result in a false negative.

If your periods are typically irregular, it can be harder to find the right time to take a pregnancy test. You may want to take a few over the course of several weeks or talk to your healthcare provider to be sure.

Other early symptoms of pregnancy to watch for include:

Your period is generally considered late once it’s been at least 30 days since the start of your last period.

Many things can cause this to happen, from routine lifestyle changes to underlying medical conditions. If your period is regularly late, make an appointment with your healthcare provider to determine the cause.