Menopause is a natural biological process that marks the end of a womans menstrual cycles. It is diagnosed after a woman has gone 12 consecutive months without a menstrual period. The age at which natural menopause occurs is generally between 45 and 55 years for women worldwide. However, the average age of menopause in the United States is approximately 51 years old. Some women may experience menopause earlier, which is called premature menopause. The years leading up to menopause, when women may have changes in their monthly cycles, hot flashes, or other symptoms, are called the menopausal transition or perimenopause. The menopausal transition most often begins between ages 45 and 55 and usually lasts about seven years but can be as long as 14 years. The duration can depend on lifestyle factors such as smoking, age it begins, and race and ethnicity.