This variable collects each person's age in ten-year groups. If age is not reported, it is imputed. For infants aged less than one year, 0 years of age is recorded.

Age is also available for 0 to 115 years singly (AGEP) and in 5-year groups (AGE5P).

All persons

Age is calculated from date of birth when provided, otherwise stated age is used. Where both sets of information are provided, date of birth is used to derive an age in years, except in circumstances where errors in the date of birth are identified. Age data is only output in whole years.

Where a respondent does not answer the age question, age is imputed using other information on the form and using an age distribution of the population. Where respondents report an age outside the acceptable range or where there were inconsistencies between age and relationship data, age is also imputed. For more information about imputation please see imputation in the Census Glossary.

The Imputation Flag for Age variable (IFAGEP) indicates if a person's age was imputed in the Census.

A question relating to age has been asked in every Census since 1911. Since 2006, respondents have had the option to report either date of birth or age in years.

For 2021, question wording changed from 'or' to 'and' in both the question wording and response area. The online form has been changed to primarily ask for date of birth (DOB) and the respondent is presented with a check box if DOB is not known so that they can enter the person’s age. This is to encourage the provision of more accurate data.

Age data, combined with sex data, is essential to produce accurate population estimates based on the Census count.

Age is used during processing as a cross check with other variables; for example, the age of the respondent determines whether particular questions asked in the Census are applicable.

Respondents occasionally make errors in reporting their age or date of birth, such as: 

• reporting their last birthday or the date they filled out their Census form rather than their date of birth
• parents filling in the form on their children's behalf and inadvertently reporting their own age or date of birth for their children
• character transposition errors
• other typographical errors (e.g. sticky key repetition). 

There are a small number of areas where there was a high level of non-response to the age question and age was imputed. The age distribution in areas where there are high levels of age imputation may not be representative of the underlying population and should be interpreted with caution. This is more noticeable in the small number of remote communities where there is a high level of age imputation (more than 20% of Census counts), combined with the reporting of Aboriginal and/or Torres Strait Islander status. The data for people where age was reported is not impacted.

Using the Imputation Flag for Age (IFAGEP), the non-response rate for Age was 4.4% in 2021. This is a decrease from 5.6% in 2016. For more information on imputation, see Census Methodology.

• Age (AGEP)
• Age in five year groups (AGE5P)
• Imputation flag for age (IFAGEP)

• Population
• People and communities
• Population: Census

This variable collects each person's age in five-year groups. If age is not reported, it is imputed. See Imputation flag for age (IFAGEP). For infants aged less than one year, 0 years of age is recorded.

Age is also available for 0 to 115 years singly (AGEP) and 10-year groups (AGE10P).

All persons

Age is calculated from date of birth when provided, otherwise stated age is used. Where both sets of information are provided, date of birth is used to derive an age in years, except in circumstances where errors in the date of birth are identified. Age data is only output in whole years.

Where a respondent does not answer the age question, age is imputed using other information on the form and using an age distribution of the population. Where respondents report an age outside the acceptable range or where there were inconsistencies between age and relationship data, age is also imputed. For more information about imputation please see imputation in the Census Glossary.

The Imputation Flag for Age variable (IFAGEP) indicates if a person's age was imputed in the Census.

A question relating to age has been asked in every Census since 1911. Since 2006, respondents have had the option to report either date of birth or age in years.

For 2021, question wording changed from 'or' to 'and' in both the question wording and response area. The online form has been changed to primarily ask for date of birth (DOB) and the respondent is presented with a check box if DOB is not known so that they can enter the person’s age. This is to encourage the provision of more accurate data.

Age data, combined with sex data, is essential to produce accurate population estimates based on the Census count.

Age is used during processing as a cross check with other variables; for example, the age of the respondent determines whether particular questions asked in the Census are applicable.

Respondents occasionally make errors in reporting their age or date of birth, such as: 

• reporting their last birthday or the date they filled out their Census form rather than their date of birth
• parents filling in the form on their children's behalf and inadvertently reporting their own age or date of birth for their children
• character transposition errors
• other typographical errors (e.g. sticky key repetition). 

There are a small number of areas where there was a high level of non-response to the age question and age was imputed. The age distribution in areas where there are high levels of age imputation may not be representative of the underlying population and should be interpreted with caution. This is more noticeable in the small number of remote communities where there is a high level of age imputation (more than 20% of Census counts), combined with the reporting of Aboriginal and/or Torres Strait Islander status. The data for people where age was reported is not impacted.

Using the Imputation Flag for Age (IFAGEP), the non-response rate for Age was 4.4% in 2021. This is a decrease from 5.6% in 2016. For more information on imputation, see Census Methodology.

• Age (AGEP)
• Age in ten year groups (AGE10P)
• Imputation flag for age (IFAGEP)

• Population
• People and communities
• Population: Census

This variable collects each person's age. If age is not reported, it is imputed. See Imputation flag for age (IFAGEP). For infants aged less than one year, 0 years of age is recorded.

Data is also available in 5 year groups (AGE5P) and 10 year groups (AGE10P).

All persons

Age is calculated from date of birth when provided, otherwise stated age is used. Where both sets of information are provided, date of birth is used to derive an age in years, except in circumstances where errors in the date of birth are identified. Age data is only output in whole years.

Where a respondent does not answer the age question, age is imputed using other information on the form and using an age distribution of the population. Where respondents report an age outside the acceptable range or where there were inconsistencies between age and relationship data, age is also imputed. For more information about imputation, please see imputation in the Census Glossary.

The Imputation flag for age (IFAGEP) variable indicates if a person's age was imputed in the Census.

A question relating to age has been asked in every Census since 1911. Since 2006, respondents have had the option to report either date of birth or age in years.

For 2021, question wording changed from 'or' to 'and' in both the question wording and response area. The online form has been changed to primarily ask for date of birth (DOB) and the respondent is presented with a check box if DOB is not known so that they can enter the person’s age. This is to encourage the provision of more accurate data.

Age data, combined with sex data, is essential to produce accurate population estimates based on the Census count.

Age is used during processing as a cross check with other variables; for example, the age of the respondent determines whether particular questions asked in the Census are applicable.

Respondents occasionally make errors in reporting their age or date of birth, such as: 

• reporting their last birthday or the date they filled out their Census form rather than their date of birth
• parents filling in the form on their children's behalf and inadvertently reporting their own age or date of birth for their children
• character transposition errors
• other typographical errors (e.g. sticky key repetition). 

Character transposition and typographical errors are particularly relevant to the online version of the Census form.

Data captured from written responses carries a small risk of character recognition error, mainly caused by poor handwriting or respondents writing outside the question box. The vast majority of individual characters written on paper forms met pre-set recognition confidence levels and were accepted without further examination. Characters that failed given recognition confidence levels, or responses where there was a discrepancy of more than three years between age last birthday and date of birth, were sent to clerical officers for further determination based on visual inspection of an image of the response.

Other checks on age (such as unlikely combinations of age and other variables) were made at various stages during processing, to ensure an acceptable level of quality was maintained.

There are a small number of areas where there was a high level of non-response to the age question and age was imputed. The age distribution in areas where there are high levels of age imputation may not be representative of the underlying population and should be interpreted with caution. This is more noticeable in the small number of remote communities where there is a high level of age imputation (more than 20% of Census counts), combined with the reporting of Aboriginal and/or Torres Strait Islander status. The data for people where age was reported is not impacted.

Using the Imputation flag for age (IFAGEP), the non-response rate for Age (AGEP) was 4.4% in 2021. This is a decrease from 5.6% in 2016. For more information on imputation, see Census Methodology.

• Age in five year groups (AGE5P)
• Age in ten year groups (AGE10P)
• Imputation flag for age (IFAGEP)
• Derivation
• Imputation
• Visitors to Australia

• Population
• People and communities
• Population: Census

This variable indicates if a person's age was imputed. Imputation is a statistical process for predicting values where no response was provided to a question and a response could not be derived.

See also, Age (AGEP).

All persons

When age is imputed this variable is coded to ‘02 Age imputed’. See Age (AGEP) for methods on how age is imputed.

No changes have been made for 2021.

Imputation flag for age (IFAGEP) can be used to identify how many respondents’ age was imputed at different geographical levels.

Using the Imputation Flag for Age (IFAGEP), the non-response rate for Age was 4.4% in 2021. This is a decrease from 5.6% in 2016. For more information on imputation, see Census Methodology.

• Age (AGEP)
• Derivation
• Imputation

• Population
• People and communities
• Population: Census
• 2021 Census methodology

This variable indicates if a person's binary sex was imputed. Imputation is a statistical process for predicting values where no response was provided to a question and a response could not be derived.

All persons

This variable is created during the processing of the Sex (SEXP) variable. When a record has sex imputed it is coded to ‘02 Sex imputed’ and where a record uses information from the Census form it is coded to ’01 Sex not imputed’.

For more information about imputation, please see the Sex (SEXP) variable and imputation in the Census Glossary.

The Imputation flag for sex (IFSEXP) variable was first used in 2016.

No changes have been made for 2021. 

There are no known data use considerations at this time.

Using the Imputation Flag for Sex (IFSEXP), the non-response rate for Sex was 4.7% in 2021. This is a decrease from 5.8% in 2016. For more information on imputation, see Census Methodology.

• Sex (SEXP)
• Derivation
• Imputation

• Population
• People and communities
• Population: Census

This variable records each person’s sex. A person's sex is based on their sex characteristics, such as their chromosomes, hormones and reproductive organs. If sex is not stated it is imputed.

See also, Imputation flag for sex (IFSEXP).

All persons

Responses to the sex question are captured from mark box responses on the form so the risk of processing error is minimal. Male, female and non-binary sex are the three options. A person can select one response only or they can select more than one response (male and non-binary sex, or female and non-binary sex). The online Census form allows respondents who select the non-binary sex response to provide further information. This field is optional and can be used to describe the circumstances specific to the person responding.

Note that data collected from the sex question will be reported in most Census data releases as ‘male’ or ‘female’ in order to maintain the quality of standard products at the small area level. Where a respondent has provided a male or female response and a non-binary sex response, the male or female response will be used to determine a binary sex variable. Otherwise, sex will be derived by a statistical process using random allocation.

Binary sex is also imputed when the question is not answered. If sex is missing on partially completed forms, it is imputed by automated and manual coding processes using relevant information provided on the incomplete form. For records that could not be resolved through this process, sex is derived by a statistical process using random allocation. For more information about imputation, please see imputation in the Census glossary.

The Imputation flag for sex (IFSEXP) variable indicates if a person's sex was imputed in the Census.

A question on sex has been asked at every Census since 1911.

In 2016, respondents had the option to respond as 'other sex'. If a person wanted to identify as other than male or female, they were instructed to call the Census Inquiry Service for information on how to identify on Census forms. To respond online, they were given specific login details to access an alternate form which allowed them to select 'other' and enter in information in a 'please specify' text box. To respond on a paper form, they were instructed to write on the right-hand side of the response area and these were checked manually to record a respondent's 'other sex' category. 

In 2021, a ‘non-binary sex’ option was added as an input category to the standard question, however the output categories for this variable are unchanged for 2021.

The question on the Census asks about a person’s sex, which is based on their sex characteristics, such as their chromosomes, hormones and reproductive organs.

Respondents were instructed to answer in the way that applies to them, with the guidance that the non-binary sex category was included to provide an option for people who are not exclusively male or female, for example people with variations in sex characteristics or who are intersex.

Feedback from respondents and members of the LGBTIQ+ community during Census enumeration identified some confusion on how to answer the question for people who are gender diverse, gender non-binary or transgender. It is therefore likely that some respondents answered based on their gender identity rather than their biological sex. Research undertaken by the ABS in developing the sex question for the Census suggests that this was also the case in previous censuses. This is not able to be quantified for respondents who selected a binary sex response, for example a person born male but living as a woman for many years may select ‘female’ as their response, noting this may be balanced out with respondents who were born female but living as a man and selecting ‘male’ as their response.

The ABS has released some analysis of the responses to ‘non-binary sex’ in an analytical article. To view the article visit Analysis of non-binary sex responses. While this article outlines some of the ways this group responded to the sex question, it also highlights the limitations of collecting data in this way. For more information see also Non-binary sex in the 2021 Census.

Using the Imputation Flag for Sex (IFSEXP), the non-response rate for Sex (SEXP) was 4.7% in 2021. This is a decrease from 5.8% in 2016. 

• Imputation flag for sex (IFSEXP)
• Derivation
• Hotdecking
• Imputation
• Non-binary sex
• Visitors to Australia

• Population
• People and communities
• Standard for Sex, Gender, Variations of Sex Characteristics and Sexual Orientation Variables
• Population: Census

This variable records the number of children ever born to each female aged 15 years and over.

Females aged 15 years and over

Data for this variable is captured automatically from written numeric responses, or the 'None' response category on the paper form. All numeric responses are accepted as reported.

This question was first asked in the 1981 Census.

For 2016, an instruction on the form to include live births only was removed, due to evidence of the sensitivities of this question which cannot be overcome effectively in a self-report questionnaire. This instruction was previously included to collect births information according the United Nations Standard.

No changes have been made for 2021.

The data may include a small proportion of persons with unusually high numbers of children ever born, as all numeric responses are accepted as reported.

For the Census online form, females aged 15 years and over were asked this question. Male respondents and people who responded only with non-binary sex were not asked this question.

The non-response rate for Number of children ever born (TISP) was 6.7% in 2021. This is a decrease from 8.0% in 2016. 

• Number of children ever born (ranges) (TISRP)
• Sex (SEXP)
• Age (AGEP)
• Parent

• Population
• People and communities
• Population: Census

This variable records the number of children ever born to each female aged 15 years and over in ranges.

Females aged 15 years and over

Data for this variable is captured automatically from written numeric responses, or the 'None' response category on the paper form. All numeric responses are accepted as reported.

This question was first asked in the 1981 Census.

For 2016, an instruction on the form to include live births only was removed, due to evidence of the sensitivities of this question which cannot be overcome effectively in a self-report questionnaire. This instruction was previously included to collect births information according the United Nations Standard.

No changes have been made for 2021.

The data may include a small proportion of persons with unusually high numbers of children ever born, as all numeric responses are accepted as reported.

For the Census online form, females aged 15 years and over were asked this question. Male respondents and people who responded only with non-binary sex were not asked this question.

This variable is derived from Number of children ever born (TISP). The non-response rate for Number of children ever born (TISP) was 6.7% in 2021. This is a decrease from 8.0% in 2016. 

• Age (AGEP)
• Number of children ever born (TISP)
• Sex (SEXP)

• Population
• People and communities
• Population: Census

This variable indicates the type of form a person used to submit their 2021 Census responses.

For the 2021 Census, information was collected in a number of ways from the Australian public. For most people, information was returned to the ABS via either an online form or a paper form.

A Census instruction letter was delivered to most dwellings in mail-out areas across Australia. In 2021, approximately 85% of dwellings were in mail-out areas. Each letter had a unique login code which respondents could use to access an online form. The letter also contained information on how to request a paper form.

All persons

This variable is not collected from a question on the Census form.

All paper forms were mailed to the ABS Data Capture Centre (DCC). Online forms were encrypted and sent securely to the ABS DCC, these forms were then decrypted and loaded into systems alongside paper forms.

This variable was created using the information obtained about the form types received at the ABS DCC. 

This variable has been included in Census basic and detailed microdata products since 2016. There have been no changes made to this variable.

In 2016, the ABS developed a new digital approach to the Census enumeration model. This approach provided a faster, more efficient, environmentally friendly Census than any previous Australian Census. The 2021 Census enumeration model was based on the successful elements of the 2016 Census with additional improvements to the way Census materials were delivered and collected.

The 2021 Census was the first time that the ABS actively encouraged households to complete and submit their Census form as soon as they received their materials, meaning this could be done before Census Night on 10 August. The letters also emphasised 12 August as a date after which the household may receive contact from the ABS. This messaging was designed to provide a ‘response window’, where previous censuses highlighted Census Night only.

• Personal form
• Household form
• Special short form
• Interviewer household form
• Enumeration
• Homelessness enumeration
• Intelligent Character Recognition (ICR)

• Sample copies of the 2021 Census paper forms
• How the data is collected
• How the data is processed
• 2021 Census of Population and Housing Australian Privacy Principle 5 Census Data Collection Notice
• What's new for 2021
• Downloads
• Glossary