Irregular periods refer to menstrual cycles that are shorter than 21 days or longer than 35 days, or cycles that vary in length from month to month. Most women have menstrual periods that last four to seven days and occur roughly every 28 days, but normal menstrual cycles can range from 21 days to 35 days. Irregular periods can affect anyone who has periods, but they are more common when you first begin menstruating or during perimenopause. Some common causes of irregular periods include changes in hormone levels, stress, certain health conditions, medications, and more. Certain health conditions are associated with missed menstrual periods, such as polycystic ovary syndrome (PCOS) and hypothyroidism. In general, the goal of treatment is to restore the balance of hormones in the body. If you have irregular periods and are concerned, it is important to speak to your doctor.