Life expectancy at birth is the average number of years a person can expect to live. This can vary by country, age and gender. Although life expectancy shows the number of years you can expect to live, it doesn't provide a full picture of how healthy those years could be.
Life expectancy is defined as the average number of years that a person could expect to live if he or she experienced the age-specific mortality rates prevalent in a given country in a particular year. It does not include the effect of any future decline in age-specific mortality rates.
Each country calculates its life expectancy according to somewhat varying methodologies. These methodological differences can affect the exact comparability of reported estimates, as different methods can change a country’s measure of life expectancy slightly.