When people talk about the gender pay gap in the UK, they often assume it is a single figure that definitively answers whether women are paid fairly. In reality, the UK measures the gender pay gap through two main lenses that serve different purposes. One is a mandatory employer reporting regime that requires large organisations to publish standardised figures. The other is a national statistic produced by the Office for National Statistics (ONS) to describe earnings patterns across the entire labour market. Both are commonly called the “gender pay gap,” but they are not interchangeable. To understand how the UK gender pay gap is measured, it helps to know which framework is being used and what question it is designed to answer.
The employer reporting system is built for transparency and comparability. It is not an individual pay audit, and it is not a direct test of equal pay for equal work. Instead, it is a structured disclosure that highlights how pay outcomes differ between men and women inside an organisation. The logic is simple: if an employer’s highest paid roles are mostly held by men, or if bonus schemes reward men and women differently over time, the published metrics will tend to show a gap. This makes the gender pay gap less about proving intent and more about revealing patterns that organisations and the public can examine.
The process begins with who must report. Employers with 250 or more employees on an annual snapshot date fall within scope. That snapshot date differs by sector: most public authority employers use 31 March, while most other employers use 5 April. The headcount is based on individuals rather than full-time equivalents, which matters because an organisation can meet the threshold even if many staff are part-time. Reporting is generally done at the level of the legal entity, which prevents organisations from blending together different parts of a corporate group to produce a smoother set of results.
Once in scope, the employer must decide who counts in the calculations, and the UK rules deliberately draw a boundary between two groups. The first group is “relevant employees,” which is used for some measures such as bonus participation. The second group is “full-pay relevant employees,” which is used for most hourly pay gap calculations. This distinction matters particularly for people on leave. The framework aims to avoid skewing hourly pay calculations with reduced pay during certain kinds of leave, while still recognising that those employees exist in the workforce and may receive bonuses over the year. As a result, employees can be included for headcount and bonus measures even when they are excluded from some hourly pay gap figures at the snapshot moment.
The definition of “pay” is also tightly controlled. For the reporting to be comparable across employers with different payroll structures, the rules specify what counts as ordinary pay and how hourly pay should be calculated. Ordinary pay typically includes core elements such as basic pay and certain allowances, while the methodology sets out how pay is converted into an hourly rate. This is important because it allows the reporting framework to handle salaried workers, hourly workers, and varied work patterns without letting each employer invent its own interpretation of “average pay.”
With the population and pay definition set, employers must publish a small number of required outputs, and these outputs are designed to show both the typical gap and the shape of pay distribution. The first set of measures is the gender pay gap for hourly pay, reported as both a mean and a median. The mean gender pay gap compares average hourly pay for men and women and expresses the difference as a percentage of men’s average hourly pay. The median gender pay gap does the same using the midpoint hourly pay for men and women. Requiring both is a practical choice. The mean can be influenced by a small number of very highly paid individuals, while the median often better reflects what a typical employee earns. Seeing both figures together can help observers infer whether the gap is concentrated among top earners or spread across the organisation.
The next requirement is pay quartiles, which push the analysis beyond averages. Employers must rank full-pay relevant employees by hourly pay and then split them into four equal-sized groups from highest paid to lowest paid. They then report what percentage of each quartile is male and what percentage is female. This is one of the most revealing parts of the framework because it exposes whether men and women are distributed differently across the pay ladder. An organisation might have a modest median pay gap but still show that women are underrepresented in the top quartile, which signals potential issues in progression, senior hiring, role allocation, or retention at higher grades.
Bonuses are measured through their own set of disclosures, reflecting how variable pay can shape earnings inequality even when base pay is tightly managed. Employers must report the mean and median bonus pay gap, using bonus payments made over the 12 months leading up to the snapshot date. They must also publish the percentage of men who received a bonus and the percentage of women who received a bonus over that same period. These measures are intended to show not only whether bonus amounts differ on average, but also whether access to bonus pay differs between men and women. Another feature of the UK approach is that the reported gap can be positive, negative, or zero, and the sign carries meaning. A positive figure typically indicates that women’s pay or bonuses are lower than men’s, while a negative figure indicates the opposite. A zero figure suggests parity as measured by the reporting method. These signs do not by themselves explain why the gap exists, but they shape how the results are interpreted and whether the organisation is likely to face questions about representation and reward structures.
Public sector reporting follows similar logic, though it sits within a broader equality duty environment. Many public bodies also provide narrative explanations alongside their figures, partly because public sector pay structures are often guided by formal grade systems and centrally influenced pay policies. The presence of a framework does not prevent a gap, but it can affect what drives it, such as workforce composition by grade, recruitment pipelines, and part-time patterns. Alongside this employer reporting regime is the ONS measure, which is often what people refer to when discussing the national gender pay gap. The ONS approach is statistical rather than organisational. It uses survey data to compare average hourly earnings of men and women across the economy, typically focusing on hourly earnings excluding overtime so comparisons are consistent. This produces a broad indicator of labour market outcomes and allows trends to be tracked over time. The employer reporting system, by contrast, is a disclosure tool that makes each large organisation publish comparable figures on a public platform, so that gaps can be seen, compared, and questioned.
In the end, the UK does not measure the gender pay gap as a single all-purpose number. It measures it through a set of defined calculations that reveal differences in hourly pay, bonus outcomes, and the gender composition of pay bands within organisations, while also tracking economy-wide earnings patterns through national statistics. Understanding how the UK gender pay gap is measured means recognising what each metric captures, what it does not capture, and why the framework focuses on patterns of representation and reward rather than making a direct legal finding about equal pay.
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