Life expectancy is a statistical measure of the estimate of the span of a life. It refers to the number of years a person can expect to live on average. Life expectancy, longevity, and maximum lifespan are not synonymous. Longevity refers to the relatively long lifespan of some members of a population, while maximum lifespan is the age at death for the longest-lived individual of a species. Life expectancy can be defined in two ways: cohort LEB is the mean length of life of a birth cohort, and can be calculated by integrating the survival curve from 0 to positive infinity, while period life expectancy is the average length of life for a hypothetical cohort assumed to be exposed, from birth through death, to the mortality rates observed at one particular period.

According to the CDC, life expectancy at birth in the United States was 76.4 years for both sexes in 2021, with males having a life expectancy of 73.5 years and females having a life expectancy of 79.3 years. However, life expectancy can vary depending on factors such as gender, race, and socioeconomic status. For example, non-Hispanic American Indian-Alaskan Native people had a life expectancy at birth of 65.2 years in 2021, which is equal to the life expectancy of the total U.S. population in 1944. Globally, life expectancy has increased by more than 6 years between 2000 and 2019, from 66.8 years in 2000 to 73.4 years in 2019.