The length of each stage of the menopause transition can vary for each individual. The average length of perimenopause is about four years. Some women may only be in this stage for a few months, while others will be in this transition phase for more than four years. If you have gone more than 12 months without having a period, you are no longer perimenopausal. However, if there are medications or medical conditions that may affect periods, it can be more difficult to know the specific stage of the menopause transition.