Life expectancy

Lore & Background

The earliest documented work on life expectancy was conducted in the 1660s by John Graunt, Christiaan Huygens, and Lodewijck Huygens. Human remains from the early Bronze Age indicate a life expectancy at birth of 24 years. In pre-modern societies, universally higher mortality rates and lower life expectancies at every age prevailed for both males and females. A combination of high infant mortality and deaths in young adulthood from accidents, epidemics, plagues, wars, and childbirth, before modern medicine was widely available, significantly lowers LEB. For example, a society with a LEB of 40 would have relatively few people dying at exactly 40: most die before 30 or after 55. In populations with high infant mortality, LEB is highly sensitive to death rates in the first few years of life, which can lead to misinterpretation; a society with a life expectancy of 30 may still commonly have a 40-year remaining timespan at age 5.

Reader's Guide

Life expectancy is a fundamental demographic measure that shapes understanding of population health and longevity. It is not synonymous with longevity (the relatively long lifespan of some members) or maximum lifespan (the age at death of the longest-lived individual). The concept is also used in plant and animal ecology, in life tables (actuarial tables), and for manufactured objects (where terms like shelf life, mean time to breakdown, and mean time between failures are used). Public health measures are credited with much of the recent increase in life expectancy. During the 20th century, despite a brief drop due to the 1918 flu pandemic, the average lifespan in the United States increased by more than 30 years, of which 25 years can be attributed to advances in public health. The COVID-19 pandemic reversed the trend of steady gain in life expectancy at birth, wiping out nearly a decade of progress. Regional variations are great, caused mostly by differences in public health, medical care, and diet. For instance, human beings are expected to live on average 60 years in Eswatini and 82.6 years in Japan. The article notes that a theoretical study shows the maximum life expectancy at birth is limited by the human life characteristic value δ, around 104 years, though some researchers argue there is no evidence for a limit on human lifespan.

Did You Know?

• The longest verified human lifespan is 122 years, 164 days, for French woman Jeanne Calment.
• In a society with a life expectancy of 30, it may be common to have a 40-year remaining timespan at age 5.

Decoding the Number: What Life Expectancy Truly Captures

Life expectancy is a statistical average—the expected additional years a person at a given age can anticipate under a particular mortality pattern. Demographers write it as e_x, with x marking the starting age; the most widely cited variant is e_0, life expectancy at birth. Two constructions exist. A cohort life expectancy follows a real group born in the same year, but it can only be finalized once every member has died. A period life expectancy is a hypothetical snapshot: what would a newborn experience if the death rates observed in one calendar year applied across the whole lifespan? Every national and international figure we encounter belongs to this second, period-based category. A critical subtlety is the number's extraordinary sensitivity to infant and early-childhood deaths. A society whose life expectancy at birth reads 40 does not mean most people die around forty; in reality, the bulk of deaths cluster well before thirty or well after fifty-five. To strip out that early-life distortion, demographers sometimes report e_5, the remaining years expected from age five onward, offering a cleaner picture of adult mortality. Because it is an average, any individual will inevitably outlive or fall short of the figure.

From Bronze Age to Modernity: A Four-Millennium Leap

Human remains from the early Bronze Age point to a life expectancy at birth of roughly 24 years. By 2019, the global average had climbed to 73.3 years. The trajectory in between was neither smooth nor uniform. In seventeenth- and eighteenth-century England, life expectancy at birth hovered around 36 years, one of the higher readings of the era, yet infant and child mortality remained far above later levels. Conditions in the early Virginia colony were harsher still, with life expectancy under 25, and in seventeenth-century New England roughly four in ten children never reached adulthood. The Industrial Revolution brought marked improvement in child survival: in London, recorded deaths among children under five fell from 74.5 percent of recorded births in 1730–49 to 31.8 percent by 1810–29, though incomplete registration and net immigration complicate those figures. English life expectancy at birth crept upward to 41 in the 1840s, 43 in the 1870s, and 46 in the 1890s, while infant mortality stayed near 150 per thousand throughout. The most dramatic gains arrived in the twentieth century. In the United States, average lifespan rose by more than 30 years over the century, and researchers attribute roughly 25 of those years to advances in public health rather than medical treatment alone, with only a brief setback from the 1918 influenza pandemic.

A World Apart: Regional Gaps and Their Drivers

Life expectancy varies enormously across the globe, and the gaps are driven primarily by differences in public health infrastructure, access to medical care, and dietary patterns. At one extreme, the average person in Eswatini can expect to live about 60 years; at the other, a Japanese resident can expect roughly 82.6 years. A 2011 analysis in The Lancet pointed to a confluence of factors behind Japan's exceptional figure: broadly equal opportunities, a strong public-health system, and a diet consistently associated with lower chronic-disease risk. Pre-modern societies, by contrast, experienced universally elevated mortality and depressed life expectancy at every age for both males and females, meaning the gap between the best-off and worst-off populations was shaped less by geography than by class and gender within a single society. Demographers do not rely on life expectancy alone when studying population structure. Aggregate measures—such as the share of a population in particular age brackets—are routinely paired with individual-based indicators like formal life expectancy to paint a fuller picture of how a population is aging, contracting, or expanding. The interplay of these metrics helps explain why two countries with similar life expectancy at birth can nonetheless have very different age distributions, a distinction that matters enormously for planning pensions, healthcare, and social services.

Expectancy, Longevity, and the Ceiling of Human Life

Life expectancy, longevity, and maximum lifespan are often conflated, yet they describe different things. Life expectancy is a population average; longevity refers to the comparatively long lives enjoyed by some members of a group; and maximum lifespan is simply the age at death of the single longest-lived individual of a species. The verified record belongs to Jeanne Calment, a French woman who lived from 21 February 1875 to 4 August 1997, reaching 122 years and 164 days. Theoretical estimates place the upper bound of human life expectancy near 125 years, while one InsideTracker analysis suggests genetic enhancements could push the ceiling to 245 years. Biologists Bryan G. Hughes and Siegfried Hekimi argued that existing data provide no evidence for a hard biological limit on human lifespan, a claim that has since been questioned on the basis of error patterns in the underlying records. A separate theoretical study proposes that the maximum life expectancy at birth is constrained by a species-specific characteristic value δ, estimated at around 104 years for humans. Beyond biology, the concept of life expectancy also appears in plant and animal ecology, in actuarial life tables, and even in engineering, where analogous terms such as mean time to breakdown and mean time between failures serve a similar statistical purpose for manufactured objects.

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