1. Stress

Stress may be one of the most common reasons for a late 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. 

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: 

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.