Population Projections: How to Read 2050 and 2100 Estimates
Understand medium-scenario population projections, uncertainty, assumptions, and the difference between a projection and a forecast.
A population projection shows what a population would look like if a set of assumptions about births, deaths, and migration unfolded. It is not a census count and it is not a future fact.
On this site, values from 2024 through 2100 use the medium scenario from the United Nations World Population Prospects 2024. Values through 2023 are historical estimates.
Projection, estimate, and forecast
These words are often blurred, but the distinction matters:
- An estimate describes a past or current population where complete counts are unavailable or need adjustment.
- A projection applies assumptions to show a conditional future.
- A forecast usually emphasizes the outcome considered most likely, often with uncertainty ranges.
The UN’s probabilistic framework produces many trajectories and prediction intervals. The published medium trajectory is a central reference, not a promise.
What drives a projection?
Three components determine population change:
- Fertility affects the number of births.
- Mortality affects survival into later ages.
- International migration moves people into and out of the population.
The existing age structure also creates momentum. A youthful country can continue growing after fertility falls because a large generation is entering reproductive ages. An older population can decline even if fertility improves because there are relatively few potential parents.
Why nearby years are usually clearer
People who will be middle-aged in 2050 are already alive today. That makes much of the 2050 age structure more constrained than the 2100 structure. By 2100, nearly every cohort shown depends heavily on future births and long-run assumptions.
In Japan, about 81% of the projected 2050 population is aged 25 or older, which means those people were born before 2026. Their number in 2050 depends mainly on survival and migration, not on future fertility.
Nigeria shows the opposite end of the horizon. Its population is projected to grow from about 242 million in 2026 to 477 million in 2100, but only about 4% of the 2100 population would be aged 75 or older, the only people in that chart born before 2026. Almost the entire 2100 pyramid rests on assumed future fertility, mortality, and migration.
Uncertainty generally expands with the projection horizon. The exact total in 2100 should never be read with the confidence of a recent estimate.
How to compare projected pyramids
When switching from 2026 to 2050 or 2100, focus on structural questions:
- Does the base widen or narrow?
- How much does the 65+ share change?
- Does a large cohort move upward through the chart?
- Is total population projected to grow while the growth rate slows?
- How do alternative fertility or migration assumptions affect the conclusion?
Our charts use the medium scenario only, so they are suitable for a clear baseline. Decisions sensitive to uncertainty should use the UN’s full dataset and prediction intervals.
Responsible language
Prefer “is projected to” over “will.” Report rounded values when precision is not useful. Name the source, revision, scenario, and dividing line between historical estimates and projections.
For example: “Under the UN WPP 2024 medium scenario, the population is projected to reach approximately X in 2050.” That sentence communicates both the figure and its conditional status. Applied to China: “Under the UN WPP 2024 medium scenario, China’s population is projected to fall from about 1.41 billion in 2026 to approximately 1.26 billion in 2050 and 633 million in 2100.” The 2100 value carries far more uncertainty than the 2050 value. The rankings of population by country in 2050 and in 2100 should be read with the same caution.
Sources
- United Nations World Population Prospects 2024
- WPP 2024 methodology report
- UN summary: global population peak expected this century
Frequently asked questions
Are population projections predictions?
They are conditional calculations based on assumptions about fertility, mortality, and migration. They describe plausible futures, not outcomes guaranteed to happen.
What is the UN medium projection?
It is the central scenario in the UN World Population Prospects, built from modeled future paths of fertility, mortality, and migration.
Why are long-term projections uncertain?
Small differences in demographic rates compound across decades, and future policy, migration, health, conflict, and behavior cannot be known precisely.