Why life expectancy changes as you get older

Life expectancy at birth averages over everyone, including those who die young. Once a person has survived to 60, all the deaths before 60 no longer apply to them. Their expected total age is therefore higher than the figure quoted at birth. This is not a special case or a statistical trick: it is what the life table says, on every row after the first.

Conditional survival, in plain language

Every published figure is conditional on something. At birth, the condition is simply being born. At 60, the condition is having reached 60 — which excludes everyone whose death would otherwise have pulled the average down. The group being described has changed, so the number describing it changes too.

Two numbers moving in opposite directions

This is why a country's life expectancy at birth of 80 is entirely compatible with an 85-year-old there having several further years expected. Both figures come from the same life table; they answer different questions.

The subtraction that does not work

A common instinct is to treat life expectancy as a fixed finishing age: 80 at birth, minus 62 years already lived, leaves 18. The life table does not work that way. The figure at birth is an average over a group that includes people who died at every age; the figure for a 62-year-old is computed only from those who reached 62, and is normally higher than the subtraction suggests.

From remaining years to expected age at death

Remaining life expectancy is easy to turn into a more familiar quantity. If a group of 70-year-olds has a remaining life expectancy of X years, then 70 + X is the average age at death of that group under the life table used. That total is often what people are really asking about when they look up life expectancy. It remains a population average produced by one table's mortality rates, not a personal expected age at death.

Why remaining years fall while expected total age rises

The two figures move in opposite directions because they measure different things. Remaining years count forward from where a person is now, so they shrink as the years already lived accumulate. Expected total age adds those lived years back in, and the group it averages over no longer contains anyone who died earlier. Living through an age band therefore lowers the years still ahead while generally raising the average age at death of the group that got there.

Why the gap is widest early in life

The size of the effect depends on how much mortality has been survived. Where death rates in infancy and childhood are substantial, reaching adulthood removes a large share of the deaths that pulled the birth figure down, so the expected total age of adults sits noticeably above life expectancy at birth. Where early-life mortality is low, surviving those ages removes little risk and the two figures stay close. This is why the gap between the birth figure and later-age figures differs so much between countries and periods.

Does surviving another year always add a year?

No. Surviving from one birthday to the next removes only the mortality of that single year, and at ages where death rates are low there is little risk to remove. The expected total age can then rise by only a fraction of a year. At ages where death rates are high, the same extra year of survival removes much more risk and moves the expected total age further. The size of the step is set by the mortality of the age band just passed, not by the calendar.

Why this does not mean survival keeps improving without limit

Rising expected total age is sometimes read as though survival gets easier with age. It does not. Age-specific death rates rise steeply at older ages in every published life table, and remaining years keep falling. Both statements are true at once: the average age at death of the surviving group creeps upward, while the years still expected for that group grow shorter.

Age conditioning is not change over time

Two different things can move a figure, and they are easy to confuse. One is age conditioning: reading a later row of the same table, for people who have already reached that age. The other is change over calendar time: a later table built from a different year's death rates. A 60-year-old's remaining life expectancy reflects both the age it is read at and the mortality schedule of the year the table describes. Comparisons should hold one of the two fixed.

The Explorer shows the remaining figure directly, for the chosen age band, sex and country, rather than the headline figure at birth. Explore years ahead.