The Office for National Statistics (ONS) has conducted a comprehensive programme of research and testing to finalise Census 2021 questions and guidance and we have published our analysis in detail, including final guidance for the question “What is your sex?” Census 2021: Final guidance for the question “What is your sex?” – Office for National Statistics (

We are continuing to ask a binary choice male or female sex question on the census. This approach is unchanged since 1801. There is a new voluntary question on gender identity for people aged 16 years and over later in the questionnaire.

We have worked closely with organisations and individuals from a wide range of representative groups over five years to ensure the census questions we ask provide the best information possible.

As with previous censuses, most people will not need help to answer the sex question, but for those that do, guidance will suggest they use sex as recorded on legal documents such as a birth certificate, gender recognition certificate or passport.

By referring to “legal documents” the guidance makes clear we are referring to government-issued documents. This is not self-identification, which was evaluated as part of a range of options but not taken forward.

This guidance will help maximise the response rate and meet user needs.

As with all census questions, no personal information is shared, data are anonymised and the aggregated statistics are important to shape policies and services.