How did people understand lifespan before anyone measured it?
Seneca wrote in 49 AD that "it is not that we have a short time to live, but that we waste a lot of it." Medieval Christians kept skulls on their desks. Memento mori. Death was certain. How certain, nobody knew. No government counted deaths by age. No insurer priced a premium by birthday.
Lifespan was a moral question. You died when God decided. The only reliable pattern: most children did not survive childhood. Reach adulthood and you might live to 50 or 60. Nobody could say how likely either outcome was.
John Graunt's Bills of Mortality (1662): the first life table
John Graunt, a London haberdasher, looked at the weekly bills of mortality the city published during plague outbreaks. He found a pattern nobody had extracted before. In Natural and Political Observations Made upon the Bills of Mortality (1662), he estimated survival at different ages. Of newborns, roughly two-thirds died before age 6. Only a handful reached 76.
This was the earliest systematic survival estimate. Graunt's table was crude. He guessed at causes of death. He had no population denominator. But he proved the question could be answered. Life expectancy at birth in 1662 London sat around 35 years. That number hid the real story: survive to age 20, and your remaining life expectancy was another three decades.
Graunt's method: count deaths, infer survivors. Every life table since has done the same thing.
Edmond Halley's Breslau table (1693): the birth of actuarial science
Edmond Halley, the comet astronomer, took Graunt's idea and made it mathematically rigorous. He used death records from Breslau (now Wrocław, Poland) for 1687 through 1691. Unlike London, Breslau had a stable population with recorded ages at death.
Halley published his table in 1693 in the Philosophical Transactions of the Royal Society. He calculated, for each age, the probability of dying before the next birthday. He introduced "years purchase": how many years of income an annuity should pay based on the buyer's age. A 30-year-old should pay more for a lifetime annuity than a 60-year-old. The 30-year-old will collect payments longer. Halley proved this with numbers, not intuition.
His table gave the first mathematically defensible survival odds. A 30-year-old had an even chance of reaching 60.
The 19th century: life insurance and the refinement of death tables
Life insurance needed precision. Charge the same premium to a 30-year-old and a 60-year-old, and the 60-year-old is a bargain. The 30-year-old is a subsidy. The Equitable Life Assurance Society, founded in London in 1762, was among the first to charge age-based premiums. They used a table derived from the Northampton bills of mortality (1735 through 1780). It underestimated lifespan. Good for policyholders. Bad for the company.
The 19th century brought better tables. The Institute of Actuaries in London, founded 1848, published the English Life Table series based on national census and death registration data. The first official English Life Table (1841) showed life expectancy at birth of 40.2 years for males and 42.2 for females. These tables became the standard for pricing pensions and insurance.
Insurance companies refined the numbers because money depended on it. A table off by one year of remaining life at age 65 could cost an insurer millions in underpriced annuities.
The 20th century: government statistical agencies take over
Life expectancy became a public-health metric. Governments needed to know whether sanitation, vaccines, and antibiotics were working. That required standardised measurement.
The key shift: period life expectancy became the headline number. This method takes death rates from a single year and applies them to a hypothetical newborn. It answers: if today's death rates persisted, how long would a newborn live on average? It does not predict how long today's newborns will actually live. Death rates change. But it is comparable across countries and years, and it is available now. You do not wait for a generation to die.
National statistical agencies took over production. The UK Office for National Statistics, the US National Center for Health Statistics, the World Health Organization, and the UN Population Division all publish figures. Each uses slightly different methods. Differences of one or two years between sources are normal.
For a deeper explanation of how period and cohort methods differ, see period vs cohort life expectancy.
The dramatic rise: life expectancy from 30 to 80+ in two centuries
The change is not gradual. It is the most significant health improvement in human history.
| Period | Life expectancy at birth (England) | What drove it |
|---|---|---|
| 1662 (Graunt) | ~35 | Baseline, plague and infant deaths |
| 1841 (English Life Table 1) | 40 | Early industrial, still high infant deaths |
| 1900 | ~48 | Germ theory starting, sanitation improving |
| 1950 | ~69 | Antibiotics, clean water, vaccination |
| 2000 | ~78 | Cardiovascular decline, cancer treatment |
| 2020 | ~80 | Stalled, COVID-19 caused temporary drop |
The rise from roughly 40 to roughly 80 in developed countries occurred mostly between 1850 and 2000. In 1850, one in five English children died before age 1. By 1950, it was one in 30. By 2000, one in 100.
Infant death reduction was the single largest contributor. Once children survived, adult improvements took over. Heart disease and stroke deaths fell sharply in the US between 1960 and 2010.
For the difference between life expectancy at birth and at age 65, see life expectancy at birth vs at 65.
Life expectancy in ancient Rome vs today: the real comparison
You will often see: "life expectancy in ancient Rome was 25 to 35 years." True at birth. Misleading.
The number is low because roughly one-third of Roman newborns died before age 1. Survive to age 10, and your remaining life expectancy was about 40 more years. You would die around 50. Reach age 20, and you could expect to live to about 55. Roman senators and wealthy landowners who survived childhood routinely lived into their 60s and 70s.
Today's life expectancy at birth of 80-plus is not higher because we have pushed the maximum human lifespan much further. The record remains 122 years, set in 1997. It is higher because almost nobody dies in childhood. In the US in 2022, infant deaths were 5.4 per 1,000 live births. In Rome, the rate exceeded 300 per 1,000.
The real comparison: a Roman who reached age 30 had about the same remaining life expectancy as a 30-year-old in a developing country today. The difference is not biology. It is clean water, vaccination, antibiotics, and obstetric care.
Where does life expectancy go from here?
Life expectancy at birth in the highest-longevity countries (Japan, Switzerland, Singapore) has reached about 84 years. The next change will come from reducing deaths at older ages, the 80s and 90s. That is harder than reducing infant deaths. Aging is complex.
Some experts project that period life expectancy at birth could reach 90 in developed countries by 2060, if cardiovascular and cancer deaths continue to decline. Others point to stalling and regional declines. The US saw life expectancy fall from 78.8 in 2014 to 76.4 in 2021, driven by drug overdoses, COVID-19, and chronic disease.
The life expectancy figure quoted in headlines is a snapshot of today's death rates. It is not a personal prediction. Use it as a planning tool, not a prophecy. The life clock shows your proportion of an assumed lifespan. The number you enter is up to you.
Who first calculated life expectancy for a whole population?
John Graunt in 1662. His Bills of Mortality was the first systematic survival estimate for London. He did not use the term "life expectancy", which came later, but he calculated how many newborns would survive to each age.
Why is Edmond Halley important for life expectancy?
Halley published the first mathematically rigorous life table in 1693 using Breslau data. He introduced "years purchase" for annuities, the foundation of actuarial science. Every modern life table descends from his method.
Did people in ancient Rome really die at 25?
No. Life expectancy at birth sat around 25 to 35, but that average was pulled down by very high infant deaths. A Roman who survived to age 20 could expect to live to about 50 or 55. The low at-birth number does not mean most adults died young.
When did life expectancy start rising fast?
Between 1850 and 1950. Clean water, sewerage, and vaccination cut infant deaths dramatically. Antibiotics after 1940 accelerated the trend. The rise from 40 to 80 in developed countries happened almost entirely in those years.
Is period life expectancy the same as how long I will live?
No. Period life expectancy uses death rates from one year and applies them across all ages. It is a snapshot, not a forecast. If you are already 40, your remaining life expectancy is higher than the at-birth figure minus 40, because you have survived childhood and young-adult risks.