Why life expectancy differs by 30 years between countries

Across the 173 countries and territories in this model, life expectancy at birth runs from 54.6 years to 84.6 years. That is a gap of exactly 30 years.

The obvious reading is that people in the shorter-lived countries die younger across the board — that a 70-year-old there is like an 85-year-old elsewhere. That reading is wrong, and the reason matters for anyone who plays a life simulator.

The gap is front-loaded

Life expectancy at birth is an average over everyone born in a given year, including the ones who never reach their fifth birthday. When a large share of babies die young, that average is dragged down hard — and it says very little about how long the survivors live.

Take Nigeria and Japan, the two ends of the range in this data set.

Roughly one child in nine dies before turning five in Nigeria. In Japan it is about one in four hundred. That single line explains most of the 29.4-year gap between the two — far more than any difference in how long a 70-year-old lives.

This is why the phrase 「average lifespan」 misleads people. It is not a description of a typical life. It is an accounting identity: total years lived, divided by total births.

What it means inside a simulation

A life simulator that samples from a life table will therefore produce two very different kinds of runs:

• In a country with low child mortality, almost every life reaches old age, and the variation between runs comes from causes of death in the last third of life.
• In a country with high child mortality, a meaningful share of runs end before school age. Those runs are short, and they feel abrupt — because they are abrupt.

This is the part people find hardest to accept. A run that ends at four years old looks like a bug, or like the game being cruel for effect. It is neither. It is the arithmetic of a country's real mortality distribution, sampled honestly.

The alternative — quietly re-rolling early deaths so every life reaches 70 — would make the simulation feel kinder and be a lie. The whole point of drawing from a life table is that the draw is not adjusted to be pleasant.

The 30 years are not evenly spread

If you could add 30 years of life expectancy to a country, where would they go? Not at the end. Almost all of the gain between the worst and best countries today comes from children surviving, and from infectious disease and childbirth becoming survivable.

That is also why life expectancy rose so fast in the twentieth century and has stalled in the twenty-first: the cheap wins — clean water, vaccines, antibiotics — were taken first. What remains is concentrated in the first few years of life and in causes that are expensive to treat.

Sources

Life expectancy and under-five mortality in this model are simplified from UN World Population Prospects 2024 (estimates through 2023), World Bank World Development Indicators, and WHO Global Health Observatory. Country weights follow annual birth counts, not population.

All 173 country pages carry the numbers used here: walkback.live/c