When an annuity is written, the life expectancy of the annuitant is taken into consideration.An annuity is a contractual arrangement in which an insurer agrees to pay an annuitant a specific sum of money at fixed intervals for a specified length of time or until the annuitant's death. It is often purchased by people looking to receive a steady income stream during retirement years.When an annuity is written, the life expectancy of the annuitant is taken into consideration. The longer the annuitant is expected to live, the less money the insurer will pay out each year, whereas if the annuitant is expected to have a shorter lifespan, the insurer will pay more each year. This is due to the fact that the insurer is obligated to pay for the annuitant's lifetime, and the likelihood of that happening varies depending on the individual's life expectancy.