Life expectancy

Human life expectancy is a way to measure how long people usually live on average. It tells us how many years a person might expect to live from a certain age, often starting from birth. There are two main ways to think about it. One way looks at people born in the same year and averages their ages when they pass away. The other way imagines a group of babies all starting life today and calculates how long they might live based on current death rates.

Long ago, during the early Bronze Age, people lived only about 24 years on average. But by 2019, the world average had risen to 73.3 years. This big change happened because of better medicine and safer living conditions. In the past, many babies didn’t survive, and young people often died from accidents, diseases, or complications during childbirth. These factors brought the average down.

Life expectancy isn’t the same as how long the longest-lived person lives, which is called maximum lifespan. It’s an average, so some people live much shorter lives, and others live much longer. Scientists also use this idea to study plants, animals, and even machines to understand how long they might last.

History

The first known studies about how long people might live were done in the 1660s by John Graunt, Christiaan Huygens, and Lodewijck Huygens. They used records to guess how long people lived on average.

Human patterns

The longest known human lifespan belongs to Jeanne Calment from France, who lived to be 122 years old. This is called the "maximum life span," meaning the most years a person has ever lived. While most people live around 125 years, some scientists think humans might live longer with better health.

Life expectancy has changed a lot over time. In the 1700s in England, people lived about 36 years on average. During the Industrial Revolution, life expectancy improved, especially for children. Today, life expectancy varies around the world. Places with good health care and healthy diets, like Japan, have higher life expectancies, while areas with less access to these resources have lower ones.

Life expectancy in 1800, 1950, and 2015 – visualization by Our World in Data

Public health improvements have greatly increased life expectancy. In the United States, average lifespan grew by over 30 years in the 20th century, mostly thanks to better health practices.

Different regions show big differences in life expectancy. For example, people in Japan often live longer than those in some parts of Africa, where health challenges like diseases affect longevity.

In 2024, the United States reached an average life expectancy of 79 years. This improvement is partly due to fewer drug-related deaths. However, life expectancy can vary based on where people live and their background.

Money and living conditions also affect how long people live. Wealthier areas often see longer lives compared to poorer ones.

Life expectancy from 1990 to 2021 in the US, UK, Netherlands, and Austria, showing a fall in US life expectancy around 2019

Generally, women live longer than men. This might be because men face more risks from things like smoking and accidents.

Life expectancy vs healthcare spending of rich OECD countries. US average of $10,447 in 2018.

Researchers study genes to understand lifespan, finding some parts of DNA that might affect how long people live healthily.

Main article: Centenarian

Era	Life expectancy at birth in years
Paleolithic	22–33
Neolithic	20–33
Bronze Age and Iron Age	26
Classical Greece	25–28
Ancient Rome	20–33
Wang clan of China, 1st century AD – 1749	35
Early Middle Ages (Europe, from the late 5th or early 6th century to the 10th century)	30–35
Pre-Columbian Mesoamerica	20–40
Late medieval English peerage	30–33
Early modern Britain (16th – 18th century)	33–40
18th-century England	25–40
Pre-Champlain Canadian Maritimes	60
18th-century Prussia	24.7
18th-century France	27.5–30
18th-century American colonies	28
Beginning of the 19th century	~29
Early 19th-century England	40
19th-century British India	25.4
19th-century world average	28.5–32
1900 world average	31–32
1950 world average	45.7–48
2019–2020 world average	72.6–73.2

Evolution and aging rate

Main article: Life history theory

Plants, animals, and humans all live for different amounts of time. One idea in science is that animals that live longer may have special genes. These genes help their bodies stay healthy for many years.

Another idea is that eating less food might help animals live longer. For example, mice and rats that eat less can live almost twice as long. Some animals, like giant tortoises, live very long lives because their bodies use energy slowly. Studies also show that animals that can fix mistakes in their DNA may live longer.

Calculation

Further information: Life table § The mathematics

A survival tree to explain the calculations of life-expectancy. Red numbers indicate a chance of survival at a specific age, and blue ones indicate age-specific death rates.

Life expectancy is a way to guess how many years a person might live on average at a certain age. It is like an estimate based on many people’s lives.

When we talk about life expectancy at birth, we mean the average number of years a newborn baby is expected to live. This number changes depending on where and when a person is born, as well as their lifestyle and healthcare.

Life expectancy can be calculated using special tables that show how many people live to each age. These tables help scientists and governments understand health and plan for the future.

k p x q x + k = k p x − k + 1 p x {\displaystyle {}_{k}p_{x}\,q_{x+k}={}_{k}p_{x}-{}_{k+1}p_{x}}

e x = E ⁡ [ K ( x ) ] = ∑ k = 0 ∞ k ⋅ Pr ( K ( x ) = k ) = ∑ k = 0 ∞ k k p x q x + k {\displaystyle e_{x}=\operatorname {E} [K(x)]=\sum _{k=0}^{\infty }k\,\cdot \Pr(K(x)=k)=\sum _{k=0}^{\infty }k\,\,_{k}p_{x}\,\,q_{x+k}}

e x = ∑ k = 1 ∞ k p x {\displaystyle e_{x}=\sum _{k=1}^{\infty }{}\,\,\,_{k}p_{x}}

Healthy life expectancy

For the past 30 years, people have studied how many years someone can live in good health. This is called healthy life expectancy (HALE). It means the average number of years a person can expect to live without sickness or injury. Since 2001, the World Health Organization has shared this information.

Healthy Life Expectancy (HALE) vs GDP per Capita in different countries

Many countries now use similar ideas to watch over the health of their people. In the 2010s, there was a big push to help people stay healthier for longer. Some ways being studied include fasting, exercise, and senolytic drugs.

Forecasting

Forecasting how long people will live is important for studying populations. This helps plan for programs that support older adults, like U.S. Social Security and pension systems. If people live longer than expected, these programs need to be ready to pay more money out.

There are two main ways to forecast life expectancy:

Forecasting life expectancy directly, often using tools like ARIMA. This is simple but does not look at changes in death rates at different ages.
Forecasting death rates for each age and then calculating life expectancy from those rates. This method is more complex but stronger and can also help find other details, like how many people survive to certain ages. One popular method is the Lee-Carter model.

Software tools like EViews, R, SAS, Stata, Matlab, and SPSS can help with these analyses. The Lee-Carter model uses special math to simplify the data and forecast future death rates. You can use tools like Professor Rob J. Hyndman's R package called 'demography'.

Policy uses

Life expectancy helps us understand how healthy and well-off a country or area is. It is one of the factors used in the Human Development Index, along with things like education and living standards.

We can also use life expectancy to describe the general health of a place. It even plays a role when people sell life insurance policies for cash. Differences in life expectancy can show why some places need better hospitals and support services.

Life expectancy vs. other measures of longevity

A scatter plot showing a weak positive correlation ($R^2=0.095$) between life expectancy and the number of physicians per 100,000 population across US states.

The number of doctors in an area can affect life expectancy. More doctors mean more help when people are sick or weak. There may be exceptions, like in Hawaii, due to other reasons.

Life expectancy is sometimes confused with how long an adult might live. But life expectancy is an average that includes everyone, even those who die before they grow up. It can help us guess how long someone might live after childhood.

As people get older, their life expectancy can change. For example, in old times, someone who lived to age 15 might live to around age 54 on average. In England from the 1300s to the 1800s, life expectancy at birth went from about 25 years to over 40 years. But for those who lived past 30, they could expect to live about 20 to 30 more years, meaning they might die around age 50 to 60.

For nobles in England in the 1300s, life expectancy at birth was about 30 to 33 years. But if a noble man lived to age 21, he could expect to live to different ages depending on the time period:

1200–1300: to age 64
1300–1400: to age 45 (because of the bubonic plague)
1400–1500: to age 69
1500–1550: to age 71

The oldest someone can live, called maximum life span, may stay the same over time. Some people lived much longer than the average life expectancy of their time, like Socrates (71), Saint Anthony the Great (105), Michelangelo (88), and John Adams (90).

However, John D. Hawks points out that while the oldest age people can live may not change, the average life expectancy has gone up because fewer adults die at younger ages today than in the past.