Menopause can start as early as age 35 in some cases. Typically, menopause begins between ages 45 and 55, with the average age in the U.S. around 52. Menopause before age 45 is considered early menopause, while menopause before age 40 is known as premature menopause or primary ovarian insufficiency (POI). Early menopause affects about 5% to 10% of women, and premature menopause affects about 1% to 3% of women. Symptoms of menopause can start a few years before the final menstrual period during a phase called perimenopause, which can begin in the mid-30s for some women. Causes of early or premature menopause include genetics, certain medical treatments, surgeries, and health conditions, but often no clear reason is found.