Reproductive rights and bodily autonomy matter in their own right. Population projections can help governments and communities plan for possible change, but they are not targets and cannot determine whether or when anyone should have children.

What do the main projections say?

A population projection estimates future population under stated assumptions about factors such as fertility, mortality and migration. The United Nations, IHME and the Wittgenstein Centre/IIASA have published different projections using different model designs, data and scenario definitions. Compare each result with its publication year and scenario label.

UN DESA: World Population Prospects 2024

The medium projection rises from 8.2 billion in 2024 to around 10.3 billion in the mid-2080s, then reaches 10.2 billion by 2100. UN DESA estimates an 80% chance of a global peak this century. Its 2100 95% prediction interval is 9.0–11.4 billion. Read the UN summary.

Wittgenstein Centre/IIASA: WIC2023, data version V15 (September 2026)

In the SSP2 medium scenario, population peaks at 10.13 billion in 2080 and declines to 9.88 billion by 2100. WIC2023 includes seven variants and uses 2020 as its reference year. Read the IIASA overview.

IHME: 2020 reference scenario

The reference scenario peaks at 9.73 billion in 2064 and declines to 8.79 billion by 2100. The 95% uncertainty interval for 2100 is 6.83–11.8 billion. This is a 2020 research projection, not a current UN estimate. Read the study record.

These figures are not interchangeable forecasts of one fixed future. The 2024 UN report itself compares the three vintages and reports different modelled outcomes. The UN prediction interval and IHME uncertainty interval also use different methods; do not present them as equivalent. The IIASA SSP2 value is a scenario result, not an uncertainty interval.

Why do projections differ?

The studies use different data vintages, model structures and assumptions. For example, WIC2023 uses 2020 as its reference year and sets out scenarios for fertility, mortality, migration and education. IHME’s 2020 paper uses its own scenarios, while UN DESA’s 2024 revision uses its official population estimates and projection framework.

A projection should therefore be quoted with its publisher, release year and scenario. A number without those details can make unlike projections look directly comparable when they are not.

What can projections tell us?

Projections can help planners consider a range of possible population sizes and age structures. They cannot tell us exactly what will happen, prescribe a population size, or justify pressure on anyone’s reproductive choices. Rights and access to voluntary healthcare, education and family planning matter in their own right.

When population and environmental change are discussed together, include the wider context: consumption, production systems, technology, inequality, policy and historical responsibility. A projection alone cannot establish the cause of an environmental outcome or assign responsibility to people based on where they live.

Frequently asked questions

Which population projection is the latest?

This page compares the versions named above: UN DESA’s 2024 revision, WIC/IIASA’s 2023 projection set (data version V15, September 2026) and IHME’s 2020 reference scenario. IIASA also publishes a separate 2025-rebased SSP update: SSP2 population is the same as in WIC2023 SSP2, while SSP1, SSP3, SSP4 and SSP5 differ from 2025 onward. Check each publisher for newer releases before quoting these figures.

Why do the UN and IHME projections differ?

They are separate research products, published in different years and based on different data, methods and assumptions. Their results and uncertainty measures should not be treated as like-for-like.

Are population projections targets?

No. Projections describe possible demographic change under assumptions. They do not set a target for population size or for anyone’s reproductive decisions.

Where can I read more?

• The World of Population Projections — a dated explainer of UN, IHME and IIASA approaches.
• The Road to 10 Billion: World Population Projections 2024 — Population Matters’ analysis of the UN DESA 2024 release.
• Population Matters: Population Solutions — rights-based approaches to healthcare, education and justice.