Life expectancy is one of the most quoted numbers in the world, and one of the most misunderstood. It is often read as a prediction of how long a person will live, or as the age at which people typically die. It is neither. It is an average built from the death rates of a whole population in a particular year, and it answers a more specific question than most people realise. This guide explains what the number actually measures, the difference between period and cohort figures, why your own expected age keeps rising as you get older, how a life table is built, and what the average can and cannot tell you.
What life expectancy measures
The figure usually quoted is life expectancy at birth. It is the average number of years a newborn would live if, throughout their life, they experienced the death rates seen across the population in one particular year. If death rates at every age stayed exactly as they were in 2023, a baby born in the United States would live on average about 79.3 years. Worldwide, the equivalent figure is about 73.2 years.
Two words in that definition carry most of the meaning. The first is average: some people in the group live far longer, and some far shorter. The second is if: the figure assumes that today’s death rates will hold for the rest of the baby’s life, which is almost never true, because medicine, living standards and public health keep changing. Life expectancy is best read as a snapshot of how healthy a population is right now, not as a forecast for any individual.
Period versus cohort
Statisticians produce two kinds of life expectancy, and the difference explains a lot of confusion. Period life expectancy, the kind almost always quoted in the news, uses the death rates of a single year for every age. It imagines a group of people living their whole lives under, say, 2023’s conditions. It is quick to calculate and good for comparing countries and years, which is why our calculators use it.
Cohort life expectancy follows a real group of people born in the same year and uses the death rates they actually experience, or are projected to experience, as they age. For people born long ago, it can be calculated from what really happened. For people alive today, it relies on projections of future improvements. When death rates are falling, as they have done for most of the last century, cohort life expectancy is higher than period life expectancy, sometimes by several years, because each generation benefits from progress that happens during its lifetime.
Official statistics offices, such as the UK’s Office for National Statistics, publish both. If you see two very different numbers for the same country, the first thing to check is whether one is period and the other cohort.
Why your expected age rises as you get older
One of the most surprising facts about life expectancy is that the older you get, the older you can expect to become. A newborn in the United States has a period life expectancy of about 79.3, but a 65-year-old can expect on average another 20.0 years, taking them to about 85.0. An 80-year-old can expect another 9.6, to about 89.6. The chart at the top of this guide shows the same pattern for the world as a whole.
This is not a statistical trick. The figure at birth includes everyone, including the minority who die young from accidents, illnesses or problems at birth. Every year you survive, you leave those risks behind, and the average for the people still alive alongside you shifts upward. So the right question for an adult is not “what is life expectancy?” but “what is the remaining life expectancy for someone my age?”, which is exactly what our peer life expectancy calculator shows.
| Age reached | US: years remaining | US: average age reached | World: years remaining | World: average age reached |
|---|---|---|---|---|
| Birth | 79.3 | 79.3 | 73.2 | 73.2 |
| 10 | 69.8 | 79.8 | 66.3 | 76.3 |
| 15 | 64.9 | 79.9 | 61.5 | 76.5 |
| 25 | 55.3 | 80.3 | 52.1 | 77.2 |
| 45 | 36.7 | 81.7 | 33.9 | 78.9 |
| 65 | 20.0 | 85.0 | 17.6 | 82.6 |
| 80 | 9.6 | 89.6 | 8.3 | 88.3 |
How a life table works
Every life expectancy figure comes from a life table, and the idea behind one is simpler than it sounds. Start with an imaginary group of 100,000 newborns. For each age, take the share of people at that age who died during the year, which statisticians call the probability of dying. Apply it to the group: if the probability of dying in the first year is 0.5 per cent, then 500 of the 100,000 die and 99,500 reach their first birthday. Apply the next age’s probability to the 99,500, and so on, all the way to the oldest ages.
At the end you have a column showing how many of the original group are still alive at each age. Add up all the years lived by everyone in the group, and divide by 100,000, and you have life expectancy at birth. To find life expectancy at, say, age 65, add up the years lived after 65 and divide by the number still alive at 65. That is why the remaining-years figure at older ages is always calculated only among people who have already survived to that age.
A simplified example. Imagine a tiny population where, of 100 people, 10 die at age 1, 20 die at 60, 40 die at 80 and 30 die at 90. Their life expectancy at birth is (10 × 1 + 20 × 60 + 40 × 80 + 30 × 90) ÷ 100 = 71.1 years. But for the 90 people who survive infancy, the average age at death is (20 × 60 + 40 × 80 + 30 × 90) ÷ 90, which is 78.9. Remove the early deaths and the average jumps by almost eight years, even though nothing about later life has changed.
Why old averages were so low
You may have read that people in the past lived to only 30 or 40. In one sense that is true: life expectancy at birth was that low for most of human history, and even in 1950 the world average was below 50. But it does not mean most adults died at 40. The main reason the averages were low is that a very large share of children died young. In 1950, roughly one child in five worldwide died before their fifth birthday, according to United Nations estimates; today it is fewer than one in 25.
As the simplified example shows, deaths in early childhood pull the average down far more than deaths in old age. Adults who made it through childhood in earlier centuries often lived into their sixties and seventies. The enormous rise in life expectancy since 1900 comes mostly from fewer babies and children dying, thanks to clean water, vaccines, better nutrition and medical care, with improvements in survival at older ages adding more in recent decades. The longest any person has been verified to live, 122 years and 164 days, was reached by Jeanne Calment of France, who died in 1997, and that record still stands.
How countries and sexes compare
Life expectancy differs a great deal around the world, and the differences are a useful measure of health and living conditions. In the UN’s 2023 estimates, life expectancy at birth was about 83.9 in Australia, 82.6 in Canada, 81.3 in the United Kingdom, 79.3 in the United States and 72.0 in India, against a world average of about 73.2. The gap between rich countries tends to come from differences in deaths in middle age, from causes such as heart disease, drug overdoses and road accidents, while gaps with lower-income countries still owe much to child and infectious-disease deaths.
Women outlive men in almost every country. In the United States the UN’s 2023 figures put women’s life expectancy at birth at about 81.8 and men’s at about 76.9, a gap of around 4.9 years. Worldwide the gap is similar, 75.9 against 70.5. Researchers think the difference comes partly from biology and partly from behaviour, with men on average more likely to smoke, drink heavily, take risks and work in dangerous jobs.
What the average cannot tell you
Life expectancy describes populations, not people. Within any country, the figure hides big differences by income, education, region, health and habits. Two people of the same age and sex in the same country can have very different prospects, and nobody’s personal future can be read from a national average. That is why every calculator on Days Counted that looks ahead uses an age you choose as a scenario, and why the peer life expectancy calculator is labelled as a population average rather than a forecast.
Used in that spirit, life expectancy is still a genuinely useful number. It is a fair summary of how a population’s health is changing, a helpful starting point for long-term planning such as pensions and savings, and a reminder that the odds improve with every year you live. If you want to think about the years ahead in a more personal way, our calculators for the time until an age you choose and for the weekends ahead let you set the age yourself.
Questions people ask
What is the life expectancy in the US?
Using the United Nations’ estimates for 2023, life expectancy at birth in the United States was about 79.3 years for both sexes combined, 81.8 for women and 76.9 for men. National statistics offices publish their own figures, which can differ slightly because of methods and timing.
If life expectancy is 79, will I live to 79?
Not necessarily. It is an average across a whole population, calculated from death rates in a single year. Many people live much longer and some much shorter, and your own chances depend on your health, habits, environment and luck.
Why does life expectancy go up as you get older?
Because each year you survive removes the chance of dying at that age. A 65-year-old has already come through the risks of infancy, youth and middle age, so the average age their peers reach is higher than the average for newborns.
What is the difference between life expectancy and lifespan?
Life expectancy is the average years lived by a group, based on death rates. Lifespan usually means the maximum length of life for a species. Human life expectancy has risen enormously, while the longest recorded human lifespan, 122 years, has not changed since 1997.
Is cohort life expectancy higher than period life expectancy?
Usually, yes, when death rates are falling over time. A cohort figure follows a group through life as conditions improve, while a period figure freezes the death rates of one year.
Sources. United Nations, World Population Prospects 2024, period life tables for 2023 (both sexes and by sex), via Our World in Data; UK Office for National Statistics, period and cohort life expectancy explained; UN Inter-agency Group for Child Mortality Estimation; Guinness World Records, oldest person ever.