Any number of changes in life, such as stress, weight gain or loss, perimenopause or medications, cause a period to show up early, according to CNN. While not necessarily cause for concern, it is important to make note of one's cycle so that to be able to track and identify changes.
One of the most common reasons for the fluctuation of periods is when a woman's body enters perimenopause, a stage that can last as long as five years before the end the child-bearing years, according to CNN. Characterized by changes in the length of the cycle, perimenopause is also typically accompanied by hot flashes, mood changes, sleep problems and anxiety.
Stress and weight fluctuations, both up and down, are also common causes for changes in one's cycle, according to CNN. These common occurrences throw hormones out of whack and easily shorten or lengthen the timeline of the cycle.
Other less common reasons for an early period include endocrine disorders, metabolic syndrome and polycystic ovary disease, according to CNN. Any changes to the cycle that last longer than three months should be discussed with a doctor. While an occasional early period is nothing to be concerned about, a change to the overall menstrual cycle could signal an underlying problem that needs to be addressed.