Difference between sex and gender

29 May 2022

This article sets out the interpretation of the terms “sex” and “gender”, which the Office for National Statistics (ONS) and UK government bodies will be using to assess how the UK is progressing towards the achievement of the UN Sustainable Development Goals (SDGs).

SDGs are a universal call to action to end poverty, protect the planet and ensure that all people enjoy peace and prosperity by 2030. The goals cover a range of areas, including health, the environment, the economy and inequalities. Sex and gender are relevant across the SDGs as a whole, but are particularly important for Goal 5: Gender equality.

As the UK’s national statistics institute, ONS is responsible for monitoring the UK’s progress towards the global SDG indicators. Part of this role includes putting the data into context. For more information about SDGs, please see our online reporting platform.

2.Definitions and differences

The UK government defines sex as:

referring to the biological aspects of an individual as determined by their anatomy, which is produced by their chromosomes, hormones and their interactions

generally male or female

something that is assigned at birth

The UK government defines gender as:

a social construction relating to behaviours and attributes based on labels of masculinity and femininity; gender identity is a personal, internal perception of oneself and so the gender category someone identifies with may not match the sex they were assigned at birth

where an individual may see themselves as a man, a woman, as having no gender, or as having a non-binary gender – where people identify as somewhere on a spectrum between man and woman

The World Health Organisation regional office for Europe describes sex as characteristics that are biologically defined, whereas gender is based on socially constructed features. They recognise that there are variations in how people experience gender based upon self-perception and expression, and how they behave.

Essentially, nearly all people are born with physical characteristics that are labelled male or female. In 1964, Robert Stoller1 coined the term gender identity, which refers to an individual’s personal concept about their gender and how they feel inside. It is a deeply held internal sense of self and is typically self-identified. Gender identity differs from sexual identity and is not related to an individual’s sexual orientation (for more information, see the Terminology page of the Gender Identity Research and Education Society). As such, the gender category with which a person identifies may not match the sex they were assigned at birth.

Gender is increasingly understood as not binary but on a spectrum. Growing numbers of people are identifying as somewhere along a continuum between man and woman, or as non-gendered (neither man nor woman) (see Gender Spectrum). Therefore, they often have their own words to describe themselves rather than using pre-defined categories of male and female (for more information, see Gender Identity Workshop, Summary of Discussions). While more people are identifying as non-binary, this is not a new concept and has existed for many years across different cultures around the world.

3.Variations in sex characteristics

Sex and gender are both generally referred to in two distinct categories: male and female or man and woman. However, there are naturally occurring instances of variations in sex characteristics (sometimes known as intersex). This is where people are born with hormones, chromosomes, anatomy or other characteristics that are neither exclusively male nor female. They are usually assigned a sex (male or female) by their family or doctor at birth as birth certificates require the sex of the child – either male or female. Individuals with variations in sex characteristics might identify as male, female, or intersex, and they may consider themselves to be a man, a woman, or to have a non-binary identity.


Transgender or trans is an umbrella term for people whose gender identity is different from the sex assigned at birth. The Equality Act 2010 contains the protected characteristic of gender reassignment, which is defined as follows:

“A person has the protected characteristic of gender reassignment if the person is proposing to undergo, is undergoing or has undergone a process (or part of a process) for the purpose of reassigning the person's sex by changing physiological or other attributes of sex.”

This definition covers a wide range of people at varying stages of transition. A person does not need to have legally changed their gender to be included within the definition of the protected characteristic, nor do they need to have had any kind of surgery. The protection extends to anyone who has been treated less favourably because of gender reassignment, regardless of whether they have that characteristic or not.

Many trans people go through a process called transitioning: changing how people see them and the way they look to align with their gender identity. It can involve changing characteristics, appearance, names and pronouns, and may include medical treatment, such as hormone therapy or surgery. Some people may not go on to have surgical procedures, but just have the “lived experience” in the gender they identify as. Definitions and terms are very personal; people who have transitioned do not necessarily identify their gender as trans. They may see their gender identity as a man or woman, or have different preferences and words to describe themselves (for more information, see Trans Data Position Paper).

Transitioning can also involve legally changing gender under the Gender Recognition Act 2004, which allows trans people to obtain a new birth certificate showing their new name and sex. It is important to note that the law in the UK treats the terms sex and gender as interchangeable. This is shown by the Gender Recognition Act allowing someone who is changing their gender to change the sex marker on their birth certificate.

The term trans is often grouped with sexual identity and orientation (for example, lesbian, gay, bisexual and transgender (LGBT)), however, it is independent of who you are attracted to and should be considered as separate.

5.Sustainable Development Goals (SDGs): gender and sex

The Sustainable Development Goals (SDGs) are a universal set of goals, underpinned by targets and indicators. They seek to eradicate inequalities, ensuring that no one is left behind. Office for National Statistics (ONS) is the focal point of UK data for the global SDG indicators.

The data used to report on the indicators are often collected by other organisations (such as the NHS and government departments) and may not match SDG requirements. Most data collected captures those who are male or female only, and in some cases is labelled sex and some cases gender. There are very few organisations that collect data on gender identity. For more information, please see the Equalities data audit.

In the SDGs, the goals and targets tend to refer to gender, for example, “Goal 5: Gender equality” and “Target 4.a: Build and upgrade education facilities that are child, disability and gender sensitive and provide safe, non-violent, inclusive and effective learning environments for all”. However, indicators refer to sex, for example, “Indicator 5.b.1: Proportion of individuals who own a mobile telephone, by sex” and “Indicator 8.5.2: Unemployment rate, by sex, age and persons with disabilities”. This makes it complex in understanding what data are required and what information needs to be collected.

The main principle of the SDGs is to “leave no one behind”. To meet this, each of these indicators are to be broken down, where relevant, by eight characteristics required by the United Nations (UN). In paragraph 74.g of Transforming our World: the 2030 Agenda for Sustainable Development, they state the disaggregations are: income, sex, age, race, ethnicity, migration status, disability and geographic location, and other characteristics relevant in national contexts. However, in paragraph 17.18 they state gender instead of sex (the other disaggregations are the same).

The terms sex and gender appear to be used interchangeably. The “other characteristics” outlined in the Agenda relate to human rights and international laws, and include sexual orientation and gender identity. This suggests that measuring both sex and gender is important to ensure that no one is left behind. However, the Equality and Human Rights Commission indicates there may be a concern when it comes to reporting, especially when data are disaggregated. Even where data on gender identity are collected accurately, the amount of data may be so small that disclosure control means the data cannot be provided.

6.Data collection: 

benefits and complexities
Sex and gender data can be collected in various ways, as: biological sex, self-defined sex and gender identity. For many people, their sex and their gender are the same, so when asked about sex or gender they do not see a difference, and will just respond “male” or “female” as appropriate.

There are many positives in collecting gender identity data. The Equality and Human Rights Commission indicates that people welcome inclusion in surveys as it provides opportunities to express their opinions and to raise the profile of gender identity in society. The Office for National Statistics (ONS) gender identity workshop suggested that gender identity data would be useful to monitor discrimination and equality, and to inform policy. It would:

assist with allocation of funding and specialist services

provide education and awareness of gender identity

be beneficial to have official, reliable data about the size of the trans population

However, there are many different challenges in collecting and reporting gender information. Gender identity is subjective and often non-binary, therefore, data collection needs to be more detailed than simply man and woman. There are the issues of confidentiality, privacy, context, which information is appropriate to ask for and whether people would answer openly.

It is important that respondents have the opportunity to identify their own gender and that they are comfortable in doing so. It was suggested in the gender identity workshop that people may not wish to divulge some information. This was more likely if they were transitioning or not “out” about their identity for fear of discrimination or harassment, or being unsure about what their information would be used for. Those who have transitioned may see this as part of their past and not want to disclose this, or have always felt they are the gender they identify with and therefore have not made a “transition”.

Under the Gender Recognition Act 2004, people who have transitioned are not required to (but can) reveal their gender history and Article 8 of the Human Rights Act 1998 says no one is required to reveal their gender identity. This could make the collection of accurate data difficult. Additionally, in some cases gender identity is not fixed but fluid, for example, with people who identify as non-binary. This could mean that you may not be reliably measuring something for all time.

7.UK data collection

Office for National Statistics (ONS) does not currently collect data on gender identity in any social surveys and there are no harmonised questions across the Government Statistical Service (GSS). However, data collection methodology and question designs are being explored. The Census White Paper: Help Shape Our Future recommended that there will be a question on gender identity (while keeping the existing question on sex) for those aged 16 years and over for the 2021 Census for England and Wales. There is a dedicated web page outlining the work carried out and further work planned. The devolved authorities in Scotland and Northern Ireland are also considering the issue in the context of their data collection.

During the consultation for the 2021 Census for England and Wales and a gender identity workshop, it was confirmed that information about gender identity for all ages was needed to inform government policy and to allocate resources and service planning. With the 2010 Equality Act specifying gender reassignment as a protected characteristic and the government agreeing to assess how to measure the size of the UK trans population, there is increasing demand for data on gender identity (for more information, see Government Response to the Women and Equalities Committee Report on Transgender Equality). The Census White Paper: Help Shape Our Future outlines the latest position regarding gender identity questions in the 2021 Census for England and Wales.

Measurement and data on a person’s sex are still useful in certain areas, for example, healthcare and fertility. There are also some sex-specific laws, though these are changing. For example, pension provision is different for males and females, with males having a higher retirement age.


Sex and gender are different concepts that are often used interchangeably. The UK government refers to sex as being biologically defined, and gender as a social construct that is an internal sense of self, whether an individual sees themselves as a man or a woman, or another gender identity. They encompass many different identities and may be non-binary (that is, not a man or a woman).

Office for National Statistics (ONS) is researching how best to collect data on gender identity. The Sustainable Development Goals (SDGs) will look to report data disaggregated by gender identity and sex where possible as part of the principle of “leave no one behind”. All SDG data can be found on our reporting platform.

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