Population projection

Projections, forecasts and estimates

An estimate measures a population that already exists. The ABS's estimated resident population starts from the Census and is updated with recorded births, deaths and migration.

A projection runs a base population forward under assumptions. The ABS describes its projections as illustrations of the change in population that would occur if the assumptions were to prevail, and states that they are not intended as predictions or forecasts. The assumptions are drawn from past trends and may not hold, so the ABS publishes several combinations of them. In demographic usage a forecast is a projection judged to describe the most likely future, and the NSW Government presents its central projections in those terms, calling them the most likely demographic future based on trends in births, deaths and migration.

How projections are made

The ABS, the NSW Government and Victoria in Future all use the cohort-component method. It starts from the population by sex and single year of age, ages each group forward one year at a time, and applies assumptions for three components.

• Fertility. The ABS medium assumption is a total fertility rate of 1.6 babies per woman from 2027.
• Mortality. The ABS medium assumption has life expectancy at birth reaching 83.0 years for males and 86.0 years for females in 2066.
• Migration. The ABS medium assumption has net overseas migration stepping down from 400,000 in 2023 to 225,000 a year from 2031–32, and separate assumptions cover movement between states and, for small areas, within them.

The ABS's current series, Population Projections, Australia, 2022 (base) to 2071, was released in November 2023 and projects Australia's population at between 34.3 and 45.9 million in 2071, up from 26 million in 2022. It is published for states, territories, and capital cities and the rest of each state. The ABS doesn't publish official projections for smaller areas.

Who publishes small-area projections

• Geoscience Australia. The ABS prepared customised projections for Geoscience Australia for SA2s and councils, from a 30 June 2022 base to 2032 by age and sex. They are not official ABS data and are owned by Geoscience Australia. SA2 figures are constrained to the ABS medium series, and council figures are converted from SA2s with no council-specific assumptions.
• NSW. The Department of Planning, Housing and Infrastructure's 2024 NSW Population Projections cover the state, councils and SA2s from a 2021 base to 2041. In Greater Sydney, small-area populations are redistributed using the Sydney Housing Supply Forecast.
• Victoria. Victoria in Future 2023 runs to 2051 for the state and major regions and to 2036 for councils, SA2s and 191 VIF small areas. The Victorian Government states that it is not an exact prediction or forecast of the future.

Why small-area projections are less certain

The further out a projection runs and the smaller the area, the larger its likely error. A study of Australian local-area projections by Wilson and colleagues (2018), cited by Wilson and Grossman (2022), found median absolute errors in total population of 2.8% after 5 years and 5.4% after 10 years, with 5% of areas off by more than 14.2% after 5 years and 23.5% after 10. Wilson and Grossman recommend warning users that projections for areas under about 5,000 people are highly error-prone.

Geoscience Australia's notes say internal migration accounts for the majority of projected change for most SA2s, so short-term swings in who moves in and out can have a significant effect on longer-term results, and figures for small SA2s and for single years of age are less reliable than totals or broad age groups. The projections don't allow for non-demographic factors such as major policy decisions.

For a site decision, comparing the projected growth in an area with what its recent estimated resident population shows, and with dwelling approvals, indicates whether the assumptions are holding.

Projections and Censible

Censible's 2026 and 2031 figures are projections, labelled as projections wherever they appear and on the Census's footing, so a change from 2021 reads as growth. Population and age start from each SA2's 2021 Census count, grown by the ABS's estimated resident population to mid-2025 and then by the Geoscience Australia SA2 projections, by sex and five-year age group, and are shared out to SA1s by each SA1's share of each age group.

About 70 other shares, such as qualifications, languages and renting, move mostly with Australia's change since 2016 where that method predicted 2021 better than no change in a backtest fitted on 2011 and 2016 at SA2 and SA1, and the rest are held at their 2021 value. Work, travel to work and the labour force are held at 2021 because that Census was taken during lockdowns in Sydney and Melbourne. Incomes are moved to 2026 with the ABS wage price index and rents with the rents series in the CPI, while mortgages, and every dollar figure after 2026, move with Australia's change in the median from 2016 to 2021. The backtest covers five years ahead, so the 2031 figures haven't been tested against a Census.

Sources: ABS, Population Projections, Australia, 2022 (base) – 2071; ABS for Geoscience Australia, Population projections 2022 (base) to 2032, LGA metadata; Wilson and Grossman, Australasian Journal of Regional Studies, 2022.