Once an roach reaches adulthood, it lives about 400 days on average. A cockroach's life is divided into two other stages before adulthood: the egg stage and a variable number of nymphal instars.
On average, the two stages of a roach's existence before adulthood take approximately 600 days, resulting in a total lifespan over all three phases of approximately 300 days or between about two and a half to three years. There is some deviation in the lifespan of specific species of roaches. There are over 3,500 different species of roaches around the world, with about 35 species common in the United States.