Life expectancy is a statistical measure of the average number of years a person or a group is expected to live, usually expressed from birth or from a specific age. It is derived from life tables that combine age-specific mortality rates to estimate remaining years of life under current conditions. Life expectancy is a summary indicator widely used in demography, public health and planning because it condenses complex mortality patterns into a single number. For a concise explanation, see definition and methods.

How life expectancy is measured

Two common concepts are period life expectancy, which uses mortality rates observed in a given year to produce a synthetic cohort, and cohort life expectancy, which follows an actual birth cohort through time. Life tables also provide life expectancy at different ages (for example, at birth or at age 65). Because infant and child mortality strongly affect life expectancy at birth, improvements in early-life survival can raise the overall figure even if mortality at older ages changes little. Technical overviews and data sources are available via statistical guides.

Main determinants and patterns

Life expectancy reflects a mix of biological, social and environmental influences. Key determinants include:

  • Public health measures and health-care access (vaccination, maternal care, emergency services).
  • Infectious disease burden, including both longstanding threats and epidemics; for historical and ongoing examples see resources on HIV/AIDS and malaria.
  • Behavioral risks such as tobacco use, diet, alcohol consumption and physical activity; more on lifestyle influences is at lifestyle and risk.
  • Socioeconomic position: income, education and living conditions shape exposure to hazards and access to care.
  • Conflict, famine and environmental hazards that can cause abrupt declines in survival.

These forces interact: for instance, economic development often reduces infectious mortality and improves nutrition, which in turn changes the profile of causes of death toward chronic diseases.

Over the last two centuries many populations have experienced large increases in life expectancy, primarily through reductions in child mortality, improved sanitation, vaccines and later medical advances such as antibiotics and cardiovascular care. This shift is sometimes described as the epidemiological transition: infectious causes decline and non-communicable diseases (heart disease, cancers, diabetes) become relatively more prominent. The pace and timing of these changes vary across countries and groups; summaries and timelines can be found at global health sources.

Global and within-country differences

Life expectancy varies widely between and within countries. Some small territories and high-income populations rank among the highest in the world; for example, certain reports list Macau among jurisdictions with top life expectancy figures (Macau report). At the national and subnational level, differences of several years are common. In many countries, people living in wealthier districts have higher life expectancy than those in deprived areas — a contrast sometimes illustrated by comparisons between affluent neighborhoods and poorer cities (Kensington example versus Glasgow example). Ethnic and racial disparities are also noted in many settings: historically, minority groups in some countries have experienced shorter average lifespans than majority groups; discussions and records appear in analyses of race and mortality.

Uses, limitations and notable facts

Life expectancy is used to monitor population health, set policy priorities, price pensions and insurance, and communicate progress. However, it has limitations: it summarizes mortality at one point in time and does not describe quality of life or distributional inequalities. Complementary measures include healthy life expectancy (years expected in good health) and lifespan inequality metrics. Researchers and policymakers consult a range of sources and models when interpreting changes; introductory resources are linked at statistical guides and method notes.

Practical implications

Understanding why life expectancy rises or falls helps target interventions: controlling infectious diseases, reducing smoking, improving prenatal care, and addressing social determinants can all raise average survival. Because causes differ by setting, effective strategies are context specific. For accessible discussions on prevention and population health strategies see public health guidance and topic pages such as malaria control and HIV prevention.