Estimated resident population (ERP) is the official estimate of the Australian population, which links people to a place of usual residence within Australia. Usual residence is the address at which a person considers themselves to currently live. ERP includes all people who usually live in Australia (regardless of nationality, citizenship or legal status), with the exception of foreign diplomatic personnel and their families.
ERP, or population estimates, for Australia and its states and territories (from now referred to as states) are prepared quarterly and released around six months after the reference date in National, state and territory population.
Population estimates for areas below the state level (from now on referred to as sub-state) are then prepared annually. Population totals for sub-state areas are released around nine months after the 30 June reference date in Regional population. Age and sex breakdowns of these estimates are then prepared and released in this product. Estimates are prepared at the Statistical Area Level 2 and Local Government Area levels, according to the Australian Statistical Geography Standard, and are aggregated or split to create estimates for other geographies. Population estimates for Statistical Areas Levels 2 to 4, Greater Capital City Statistical Areas and Local Government Areas are available in this product.
The estimates in this issue are consistent with the total sub-state estimates released on 26 March 2024 in Regional population, 2022-23 and the state estimates by age and sex released on 21 March 2024 in National, state and territory population, September 2023. The next scheduled release of total sub-state estimates is on 27 March 2025, and sub-state estimates by age and sex is on 28 August 2025.
Method
ERP as at 30 June in a Census year is calculated by adjusting Census counts of Australian usual residents to account for residents temporarily overseas, people missed or counted twice in the Census (based on the Post Enumeration Survey), and for the births, deaths and migration that happened between 30 June and Census night.
At the national and state levels, ERP is updated from the Census base every three months by taking the population estimate at the start of the quarter and adding the components of population change: natural increase (births minus deaths), net overseas migration and (in the case of state populations) net interstate migration. This is known as the component method, and uses the demographic balancing equation:
\(P_{t+1} = P_t + B - D + NOM + NIM\) where:
\(P_t\) = the estimated resident population at time point \(t\)
\(P_{t+1}\) = the estimated resident population at time point \(t+1\)
\(B\) = the number of births occurring between \(t\) and \(t+1\)
\(D\) = the number of deaths occurring between \(t\) and \(t+1\)
\(NOM\) = net overseas migration occurring between \(t\) and \(t+1\)
\(NIM\) = net interstate migration occurring between \(t\) and \(t+1\)
At the national level, net interstate migration is zero.
For Statistical Areas Level 2 (SA2s) and Local Government Areas (LGAs), population estimates are updated from the Census base annually as at 30 June also using the component method. That is, by taking the estimate at the start of the financial year and adding natural increase (which can be negative), and net overseas and internal migration (moves between and within the states). Total estimates for each SA2 and LGA are calculated first, and then broken down by age and sex by ageing the previous year's population by one year, and incorporating the components - births (by sex), and deaths, internal and overseas migration (by age and sex). The components for sub-state areas are calculated by breaking down state-level component estimates, ensuring consistency between the state and sub-state population and component data. Components at the LGA level are constrained to those at the SA2 level to ensure consistency between these two geographies.
Once the estimates are updated, they are scrutinised and validated by ABS analysts. For areas where the components are of insufficient quality, adjustments are made. In some small areas, population change since the previous Census is assumed to be zero in the absence of reliable component data.
To provide an indication of ERP by age and sex below the SA2 level, population estimates are calculated for Statistical Areas Level 1 (SA1s). For a Census year, total SA2 estimates are apportioned across SA1s using usual residence Census counts. In postcensal years, the total SA2 estimates are apportioned across SA1s by taking into account population change implied by Medicare and electoral roll counts at the SA1 level. These SA1 populations are then broken down by age and sex by ageing the previous year's population, with age distributions for selected areas held static. Estimates for SA1s are aggregated to regions such as Remoteness Areas. For areas that cannot be built up from whole SA1s, such as electoral divisions and Postal Areas, Mesh Block Census counts are used to estimate the share of the SA1 population that resides in those areas. By these means, population estimates for areas other than those provided in this product (including SA1s) may be available on request via the ABS website.
Rebasing
After each Census, the ABS uses Census counts to construct a new base population figure for 30 June of the Census year. Rebasing is the process of updating population estimates for the five years between Censuses, to incorporate information from the most recent Census. For further information see Methodology used in final rebased population estimates, June 2021.
Rebased population estimates by age and sex for each sub-state area incorporate the previous and following Census year estimates, by age cohort and sex. They are constrained to a rebased total population for each intercensal year.
As a result of the rebasing process, the components by age and sex (internal and overseas migration) for 2016-17 to 2020-21 published in previous issues of this product no longer sum to rebased population change by age and sex for these years.
Accuracy and coherence
Component data (births, deaths and overseas and internal migration) are confidentialised and constrained to add to the relevant state component estimates by age and sex. The resultant ERPs are subsequently constrained to state population estimates by age and sex. As a result of confidentialisation and forced additivity, estimates of under three people should be regarded as synthetic and only exist to ensure additivity to higher levels. While output is presented by five-year age group, all calculations are made at single year of age level. Population estimates based on single year of age may be available on request via the ABS website.
While sub-state ERP by age and sex is consistent with state ERP by age and sex, small differences arise between aggregated sub-state components by age and otherwise published state components by age. This is due to the different reference period of sub-state ERP (annual as at 30 June) and state ERP (quarterly), as the age of a person at the end of the financial year can be different to the age of that person at the end of each quarter.
The estimates in this product are subject to some error. Some caution should be exercised when using the estimates, especially for areas with very small populations. Areas with a total population of less than 1,000 people are excluded from commentary.
Status
To meet the competing demands for accuracy and timeliness, there are several versions of sub-state population estimates. Preliminary estimates by age and sex are available around 14 months after the reference date with revised estimates 12 months later. Rebased and final estimates are made available after each Census, when revisions are made to the estimates for all years in the previous intercensal period.
The status of annual sub-state ERP and components can change over time, from preliminary to revised to final, as new component data becomes available at the state level. The estimates in this product are final for 2001 to 2021, revised for 2022 and preliminary for 2023.
More information on the method, accuracy and status of these estimates is contained in Regional population, methodology.