There are several different ways to count the stages of Alzheimer's, because there is no single, standard classification.
Most physicians refer to three main stages: early (mild), middle (moderate), and late (severe). Some physicians and organizations, including the Alzheimer's Association, refer to seven stages of Alzheimer's disease, with stage 1 being "no impairment." Others refer to four stages of Alzheimer's or other forms of dementia: mild, moderate, moderately severe, and severe.
Whatever the stage names, because dementia of the Alzheimer's type is a progressive disease, everyone travels through its stages in the same order. The length of time a person spends in each stage is highly individual, however. Some people move through the disease from diagnosis to death in three years, while others live 20 years or longer after an early-stage diagnosis.