Population Projections, Australia methodology

ABS population projections are based on a series of assumptions on future levels of fertility, mortality, net overseas migration and net interstate migration. Assumptions are derived from an analysis of data sourced from a variety of institutional environments. Much of this is administrative by-product data collected by other organisations. Assumptions on fertility and mortality are based on births and deaths statistics from registers administered by State and Territory Registrars of Births, Deaths and Marriages. Overseas migration data is sourced from Australian Government Department of Home Affairs processing systems, visa information, and incoming passenger cards. This is used to make assumptions about future levels of net overseas migration. Medicare change of address data is used to estimate interstate migration, from which assumptions on future levels of net interstate migration are derived.

The 2021 Census and Post Enumeration Survey (PES) data determine a base population from which estimated resident population (ERP) is calculated. The ERP for the latest available year is the base population for the population projections. For information on the institutional environment of the Australian Bureau of Statistics (ABS), refer to ABS Institutional Environment.

Population projections inform future changes in the population of Australia, such as population growth/decline and changes in age structure, and are therefore used in a variety of key planning decisions. Projections are published for the states, territories, capital cities and rest of states, by single year of age and sex. Projected numbers of births, deaths and net overseas and internal migrants are also published.

Assumptions on future levels of fertility, mortality, net overseas migration and net interstate migration are formulated on the basis of demographic trends over the past decade and longer, both in Australia and overseas, in consultation with various individuals and government department representatives, at both the national and state/territory level.

ABS population projections are compiled and published every five years; typically two to three years following the Census.

ABS population projections are based on a number of assumptions on future levels of fertility, mortality, net overseas migration and net interstate migration.

While the assumptions are formulated on the basis of past demographic trends, both in Australia and overseas, there is no certainty that any of the assumptions will be realised. In addition, the assumptions do not attempt to allow for non-demographic factors (such as major government policy decisions, economic factors, catastrophes, wars, epidemics or significant health treatment improvements) which may affect future demographic behaviour or outcomes.

Data used in the formulation of the assumptions are subject to non-sampling error. For more information on the accuracy of these component data collections, refer to Quality Declaration Summary - Australian Demographic Statistics.

As the assumptions used in each successive set of population projections incorporate recent trends, comparison of data across issues of this publication is not undertaken.

ABS population projections are not intended as predictions or forecasts, and should not be considered as such. Rather, they are illustrations of growth and change in the population that would occur if the assumptions were to prevail over the projection period. As future levels of fertility, mortality, overseas migration and internal migration are unpredictable, two or more assumptions have been made for each component. These are intended to illustrate a range of possible future scenarios.

For more information on the method used to compile ABS population projections refer to Demographic Estimates and Projections: Concepts, Sources and Methods and the Assumptions section of Population Projections, Australia.

ABS population projections are available in a variety of formats on the ABS website:

• Time Series Spreadsheets (in Excel format) for Australia and the states and territories, by single year of age and sex, for three selected projection series (high, medium and low);
• ABS Data Explorer datasets containing population projections for Australia, the states, territories, capital cities and rest of state, by single year of age and sex, for all projection series; and
• Two data cubes (in Excel format). The first data cube contains population projections, components of change and summary statistics for Australia, the states, territories, capital cities and rest of state, for three selected projection series (high, medium and low). The second data cube contains projection assumptions.

If the information you require is not available as a standard product, then ABS Consultancy Services can help you with customised services to suit your needs. For inquiries contact the National Information and Referral Service on 1300 135 070. Alternatively email client.services@abs.gov.au.

Under a '12/16 month rule', incoming overseas travellers (who are not currently counted in the population) must be resident in Australia for a total period of 12 months or more, during the 16 month follow-up period to then be added to the estimated resident population. Similarly, those travellers departing Australia (who are currently counted in the population) must be absent from Australia for a total of 12 months or more during the 16 month follow-up period to then be subtracted from the estimated resident population.

The 12/16 month rule does not have to be continuous and takes account of those persons who may have left Australia briefly and returned, while still being resident for 12 months out of 16. Similarly, it takes account of Australians who live most of the time overseas but periodically return to Australia for short periods.

The ASGS brings all the regions for which the ABS publishes statistics within the one framework and has been in use for the collection and dissemination of geographically classified statistics since 1 July 2011. It is the current framework for understanding and interpreting the geographical context of statistics published by the ABS. For further information refer to Australian Statistical Geography Standard (ASGS) Edition 3.

The dependency ratio is a measure used to compare the size of the 'working age' population to the size of the non-working age population, calculated as the sum of people aged 0-14 and 65 years and over divided by the number of people aged 15-64 years, multiplied by 100.

Age-specific death rates are the number of deaths (on either an occurred or registered basis) during the calendar year at a specified age per 1,000 of the estimated resident population of the same age at mid-point of the year (30 June). Pro rata adjustment is made with respect to deaths for which the age of the deceased is not given.

Age-specific fertility rates are the number of live births occurring during the calendar year, according to the age of the mother, per 1,000 of the female estimated resident population of the same age at 30 June. For calculating these rates, births to mothers under 15 years are included in the 15 year–old age group, and births to mothers aged 50 years and over are included in the 49 year–old age group.

The delivery of a child, irrespective of the duration of pregnancy, who, after being born, breathes or shows any evidence of life such as a heartbeat.

Refers to the Greater Capital City Statistical Areas of states and territories as defined in the Australian Statistical Geography Standard.

A census is the complete enumeration of a specific population at a point in time (as opposed to a survey, which enumerates a sample of the population). When the word is capitalised, "Census" refers to the national Census of Population and Housing. The Census is run by the ABS every five years and aims to count every person in Australia on Census night.

The permanent disappearance of all evidence of life after birth has taken place. The definition excludes deaths prior to live birth.

For the purposes of the Deaths and Causes of Death collections compiled by the ABS, a death refers to any death which occurs in, or en route to Australia and is registered with a state or territory Registry of Births, Deaths and Marriages.

Represent the socioeconomic area of each of the eight state and territory capital cities. GCCSA boundaries represent a broad socioeconomic definition of each capital city, they contain not only the urban area of the capital city, but also surrounding and non-urban areas where much of the population has strong links to the capital city, through for example, commuting to work. For further information refer to Australian Statistical Geography Standard (ASGS) Edition 3.

The movement of people over a state or territory boundary for the purpose of changing their place of usual residence. Net interstate migration is the number of arrivals minus the number of departures.

Life expectancy refers to the average number of additional years a person of a given age and sex might expect to live if the age-specific death rates of the given period continued throughout his or her lifetime.

A life table is a statistical model used to represent the mortality experience of a population. In its simplest form, a life table is generated from age-specific death rates and the resulting values are used to measure mortality, survivorship and life expectancy. The life table functions relevant to population projections are:

• qx - the proportion of persons dying between exact age x and exact age x+1. It is the mortality rate, from which other functions of the life table are derived; and
• ex - life expectancy at age x.

The age at which half the population is older and half is younger.

The number of births minus the number of deaths.

The net gain or loss of population through immigration to Australia and emigration from Australia.

Incoming international travellers who stay in Australia for 12 months or more over a 16-month period, who are not currently counted within the population, and are then added to the population.

Outgoing international travellers who leave Australia for 12 months or more over a 16-month period, who are currently counted within the population, and are then subtracted from the population.

Change in population over a particular period. Population growth is the sum of natural increase, net overseas migration and (for states and territories) net interstate migration. For periods prior to the latest Census, population growth also includes intercensal difference.

Population change over a period as a proportion of the population at the beginning of the period, expressed as a percentage.

The ABS uses the cohort-component method for producing population projections of Australia, the states, territories, capital cities and balances of state. This method begins with a base population for each sex by single year of age and advances it year by year, for each year in the projection period, by applying assumptions regarding future fertility, mortality and migration. The assumptions are based on demographic trends over the past decade and longer, both in Australia and internationally. The projections are not predictions or forecasts, but are simply illustrations of the change in population which would occur if the assumptions were to prevail over the projection period. A number of projections are produced by the ABS to show a range of possible future outcomes.

Replacement level fertility is the number of babies a female would need to have over her reproductive life span to replace herself and her partner. Given the current mortality of females up to age 49 years, replacement fertility is estimated at 2.1 babies per female.

Within each state and the Northern Territory, the area not defined as being part of the Greater Capital City is represented by a Rest of State region. The Australian Capital Territory does not have a Rest of State region.

The number of males per 100 females in a particular population. For example, sex ratio at birth is the number of male births per 100 female births.

The death rate (deaths per 1,000 or per 100,000) of a population, adjusted to remove the effects of the population’s age composition, allowing comparison of rates across populations with different age compositions. 

The sum of age-specific fertility rates (live births at each age of mother per female population of that age) divided by 1,000. It represents the number of children a female would bear during her lifetime if she experienced current age-specific fertility rates at each age of her reproductive life (ages 15-49).

Within Australia, usual residence is the address of the dwelling at which a person considers themselves to currently live, either having lived there for some time or intending to live there for some time.

The usual residence of a newborn is that of the mother.