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Quick answer

There is no legal right to a four-day working week in the UK. Employees can make a day-one flexible working request under the Employment Relations (Flexible Working) Act 2023, but employers can refuse it on statutory grounds. The 2022 UK pilot showed strong results for knowledge-work businesses, but the model is not universally applicable. Any switch requires a contractual change agreed with the employee.

The two models: compressed vs reduced hours

Before getting into the evidence and the law, it is worth being precise about what "four-day week" actually means, because the term covers two very different arrangements:

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Model one
Compressed week
Same contracted hours, four days instead of five. Typically 40 hours over four days (four ten-hour days). Pay stays the same. Productivity expectation stays the same. The employee is simply doing the same work in a different pattern.
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Model two
Reduced hours
Genuinely fewer hours. The employer absorbs the cost or accepts reduced output, usually framed as maintaining output through greater focus. The 2022 UK pilot used this model: 100% pay, 80% of hours, targeting 100% of previous productivity.
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Key difference
Hours worked
Compressed means the same hours rearranged. Reduced means genuinely fewer hours. The research evidence, the employment law treatment, and the impact on annual leave are all different depending on which model is used.

The distinction matters legally because a compressed arrangement does not change the employee's contracted hours and therefore does not trigger any change to pay or most statutory entitlements. A reduced-hours arrangement does change contracted hours and requires a formal contractual variation agreed between employer and employee.

Most public debate and most of the research evidence concerns the reduced-hours model. When people say "the four-day week works", they typically mean the reduced-hours version.

What the 2022 UK trial found

In 2022, the UK ran one of the largest real-world trials of a reduced-hours four-day working week. The trial was coordinated by 4 Day Week Global in partnership with the Autonomy thinktank and researchers from Cambridge University and Boston College in the United States.

Who took part

Sixty-one UK companies with approximately 2,900 workers participated. The pilot ran from June to December 2022. Companies kept their workers on 100% of their normal pay while reducing their contracted working time to 80%, with the goal of achieving 100% of previous productivity through better focus, reduced unproductive time, and restructured work processes.

What the researchers found

Results were published in February 2023. According to the researchers' report:

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Interpret the trial results carefully
The 2022 UK trial was not a randomised controlled experiment. Companies self-selected to participate, which means the sample is biased towards businesses that already believed the model might work. Results came from self-reported data alongside researcher observation. The trial cohort was predominantly office-based and professional services firms. The strong results are genuine and consistent with international research, but they should not be read as guaranteed outcomes for all business types.

International context

The UK trial was part of a wider global programme. Parallel pilots in Ireland, the United States, Australia, New Zealand and Canada ran in the same period and reported broadly similar results. Iceland had run an earlier public sector pilot (2015 to 2019) covering more than 2,500 workers, with findings that included maintained or improved productivity and significant improvements in worker wellbeing. Portugal launched a government-sponsored pilot in 2023.

Where things stand in 2026

As of June 2026, there is no government mandate and no legislation requiring or specifically enabling a four-day working week in the UK. The Labour government that came to power in July 2024 did not include a four-day week mandate in the Employment Rights Act 2025, which focused on zero-hours contracts, fire and rehire practices, trade union rights and unfair dismissal protections.

What has changed is the voluntary adoption rate. A number of large and medium-sized UK employers have permanently shifted to a four-day week following their participation in or observation of the 2022 trial. Tech companies, professional services firms, marketing agencies and some charities have led the change. In sectors where the model does not fit operationally, adoption has been minimal.

Employee awareness and interest has increased. More employees are making flexible working requests specifically to move to a four-day schedule. Employers receiving these requests need to understand both what the law requires and what a proper assessment of the arrangement involves.

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Related: unlimited holiday allowance
The four-day week and unlimited holiday are both pitched as progressive employee benefits, but the evidence on both is nuanced. Just as the four-day week requires careful implementation to work, unlimited leave schemes consistently show employees taking fewer days under them, not more. The honest review of unlimited holiday allowance in the UK covers why defined entitlements with good tooling tend to outperform unlimited schemes for most UK SMEs.

There is no right to a four-day week

The Working Time Regulations 1998 cap the average working week at 48 hours for most workers (with a voluntary opt-out available). They set the minimum rest and leave entitlements. They say nothing about the minimum number of days an employee must work, so there is no statutory floor below which an employer cannot require fewer days. A four-day week is entirely lawful; it is also not a right.

Flexible working requests

The most relevant legal route for an employee who wants to move to a four-day week is a flexible working request. The Employment Relations (Flexible Working) Act 2023 amended the right significantly:

Rule Before April 2024 From 6 April 2024
Who can request Employees with 26 weeks' continuous service All employees from day one
How many requests per year One Two
Response deadline 3 months 2 months
Consultation requirement Required if refusing Required before any decision

Crucially, a flexible working request is not a right to the arrangement requested. The employer must consider the request properly and consult with the employee, but can refuse it on any of eight statutory business grounds:

  1. The burden of additional costs
  2. Detrimental effect on ability to meet customer demand
  3. Inability to reorganise work among existing staff
  4. Inability to recruit additional staff
  5. Detrimental impact on quality
  6. Detrimental impact on performance
  7. Insufficiency of work during the proposed hours
  8. Planned structural changes to the business

An employer does not need to prove the ground beyond doubt, but it must be genuinely applicable. A blanket refusal without proper consideration is an employment law risk. Employees can appeal internally and can ultimately bring a claim to an Employment Tribunal if dismissed or subjected to a detriment for making the request.

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What a proper refusal looks like
ACAS guidance recommends that employers hold a meeting with the employee to discuss the request before deciding. If you refuse, write to the employee explaining which of the eight grounds applies and why. Keep a record of the process. A refusal that cites a genuine operational reason and follows the ACAS process is very unlikely to generate a successful tribunal claim. A refusal that simply says "no" without explanation is not.

Changing an existing contract

If an employer decides to introduce a four-day week, it requires a formal variation of contract for each affected employee. This must be agreed: an employer cannot unilaterally reduce an employee's contracted hours without their consent (that would be a breach of contract and potentially an unlawful deduction from wages if pay is reduced). The variation should be documented in writing and signed by both parties. If existing employment contracts are silent on the number of working days, take employment law advice on how to document the change.

Annual leave on a four-day week

Annual leave entitlement under the Working Time Regulations 1998 is expressed in weeks (5.6 weeks for most employees, with a maximum of 28 days for a five-day-a-week worker). Moving to a four-day week changes how the days figure is calculated.

A full-time employee working five days a week has a statutory entitlement of 5.6 weeks, which equals 28 days (5 x 5.6). If the same employee moves to a four-day week, their statutory entitlement in days falls to 22.4 days (4 x 5.6). Pay stays the same if this is a reduced-hours arrangement with maintained pay, but the days figure changes.

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Example: moving from 5 days to 4 days
Priya works five days a week with a 28-day annual leave allowance (which includes bank holidays). If she moves to a four-day week compressed (same total hours), her contracted working pattern changes but the days she works in a week falls to four. Her annual leave in days becomes 4 x 5.6 = 22.4 days. Bank holidays: only bank holidays falling on her four working days count towards her allowance. This calculation is the same as any part-time worker. Use the part-time holiday calculator to work it out precisely.

The same logic applies to bank holidays. If an employee works Monday to Thursday, Good Friday does not fall on a day they would normally work and does not need to be given as paid leave (or deducted from their allowance). If they work Tuesday to Friday, Easter Monday creates the same position. This can require rethinking bank holiday treatment for individual employees. For a detailed guide to bank holiday policy options, see the bank holiday policy guide.

Book Time Off
Set individual allowances when working patterns change

When an employee moves to a four-day week, their annual leave allowance in days changes. Book Time Off lets you set a custom allowance for each person independently: update one employee's entitlement to 22.4 days without touching anyone else's. Days used and days remaining update automatically from there.

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Is it right for your business?

The honest answer to this question depends heavily on what your business does. The 2022 UK trial was dominated by professional services, technology, marketing and knowledge-work businesses where output is measured by results rather than hours present. For those sectors, the model has a plausible mechanism: reduce unproductive time (unnecessary meetings, context-switching, interruptions), maintain focus on real output, and give employees a longer recovery window.

Sector / business type Suitability Key consideration
Office-based professional services, tech, marketing, finance, creative High, if output is measurable and meetings can be reduced Requires genuine reorganisation of work, not just compressing the same schedule
Retail, hospitality, customer-facing with contracted service hours Low for reduced-hours model; compressed may work for some roles Physical presence is directly tied to service delivery; fewer days means less coverage or higher headcount cost
Healthcare, care services Low for reduced-hours; shift-pattern adjustments may be more relevant Staffing ratios and patient care standards constrain schedule flexibility at the business level
Manufacturing, logistics Depends on process; some lines can adapt, others cannot Machine utilisation and production schedules may require continuous operation regardless of individual working patterns
Mixed teams (some roles eligible, others not) Partial implementation possible, with care Creates two-tier treatment within the same business; fairness and resentment risks need managing explicitly

Partial implementations, where some roles can adopt a four-day week and others cannot, are common but require careful management. The risk of resentment between teams where one group has a different schedule is real and should be acknowledged openly rather than ignored.

How to run a trial

For employers who have assessed the suitability question and want to test the model, running a structured trial before making a permanent change is strongly advisable. The 2022 UK cohort's near-universal continuation rate reflects in part that they ran proper trials rather than permanent switches.

Define what "success" means before you start
Decide in advance which metrics you will track and what result would lead you to continue or abandon the trial. Typical measures include customer satisfaction scores, project delivery times, revenue or billable hours, sickness absence rates and staff retention. Without agreed criteria set before the trial, the decision at the end becomes subjective and politically difficult. A six-month trial is the most useful minimum window: the first month usually shows adjustment noise, and the real steady-state emerges over months three to six.
Audit your current working patterns for time waste
A four-day week only works if the missing day's productivity genuinely gets absorbed by improved focus elsewhere. Before launching the trial, run a deliberate audit of where time goes: meeting culture, email volume, context-switching, unplanned interruptions. Most organisations find significant room to recover time here. If your current five days are genuinely as efficient as they can be, a four-day week will create shortfalls rather than absorb them. Common changes include meeting-free time blocks, no-meeting Fridays during the trial period, asynchronous communication norms and email response time expectations.
Agree the trial terms contractually with employees
A trial is still a contractual arrangement. Document it in writing as a temporary variation for the duration of the pilot, with an agreed review date and a clear statement that the outcome may be continuation, modification or return to the original pattern. Do not simply stop enforcing the existing contract: that creates a permanent implied variation. Employees should sign the temporary variation agreement. For small employers, a simple letter confirming the trial terms and the review process is sufficient, but it needs to exist.
Communicate clearly with clients and customers
If your business has client-facing commitments with response time expectations, a four-day week changes the picture unless you plan rotas to maintain coverage. Decide before the trial whether you will inform clients, how you will handle urgent requests on the fifth day, and whether you will stagger your team's off day so coverage is maintained Monday to Friday across the team as a whole. Staggering is common: one group takes Monday off, another takes Friday off, and the business maintains five-day coverage as an organisation even though individuals work four days.
Review, decide and implement the outcome properly
At the end of the trial period, measure the agreed metrics and compare against the baseline. If you continue, make the arrangement permanent via a proper contractual variation for each employee. If you stop, use the temporary variation's review clause to revert. Either way, communicate the decision clearly and explain the reasoning. If continuing, update your employment contracts, HR records and annual leave calculations for affected employees. Book Time Off lets you update individual allowances in the same session.
Book Time Off
Manage flexible arrangements without a spreadsheet

When different team members work different patterns, keeping leave entitlements, allowances and approvals consistent gets complicated fast on a shared spreadsheet. Book Time Off handles custom per-person allowances, leave type tracking and one-click approvals across the whole team, regardless of working pattern. Staggered four-day arrangements, mixed full-time and part-time teams, and individual flexible working agreements all work in one place.

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Sources and further reading

GOV.UK Flexible working: the right to request and employers' duty to consider (GOV.UK)
ACAS Flexible working guidance for employers (ACAS)
legislation.gov.uk Working Time Regulations 1998
legislation.gov.uk Employment Relations (Flexible Working) Act 2023
legislation.gov.uk Employment Rights Act 1996, s.80F (flexible working right as amended)
4 Day Week Global / Cambridge University / Boston College / Autonomy The results of the 2022 UK six-month pilot were published in February 2023 in a report co-authored by researchers from Cambridge University and Boston College in partnership with the Autonomy thinktank. This is a research source, not a government publication; figures are drawn from self-reported employer data and independent researcher observation during the trial period.

Frequently asked questions

Is there a legal right to a four-day work week in the UK?
No. There is no statutory right to work a four-day week. Employees have a day-one right to make a flexible working request under the Employment Relations (Flexible Working) Act 2023 (in force from 6 April 2024), but the employer can refuse it on any of eight statutory business grounds. The Working Time Regulations 1998 set a maximum average working week of 48 hours, but say nothing about the minimum number of days. A four-day week is a contractual arrangement, not a statutory entitlement.
What is the difference between a compressed four-day week and a reduced-hours four-day week?
A compressed four-day week means the same contracted hours spread across four days rather than five, typically resulting in four ten-hour days. Total weekly hours are unchanged and pay stays the same. A reduced-hours four-day week means the employee genuinely works fewer hours per week and is paid less accordingly, or the employer absorbs the cost as a retention or wellbeing investment. The UK 2022 pilot used the reduced-hours model, aiming for 100% productivity at 80% of hours for 100% pay.
What happened in the UK four-day week trial?
The UK pilot ran from June to December 2022. Sixty-one companies with approximately 2,900 workers took part. Researchers from Cambridge University, Boston College and the Autonomy thinktank evaluated the results. Ninety-two percent of participating companies decided to continue with the four-day week after the trial ended. Eighteen confirmed a permanent switch. Reported benefits included falls in sickness absence and staff turnover, with no significant negative effect on revenue. The trial used the 100-80-100 model: 100% pay, 80% of hours, targeting 100% of previous productivity.
How do you calculate annual leave for someone on a four-day week?
Statutory annual leave is 5.6 weeks, applied to the employee's working pattern. For someone working four days a week, 5.6 weeks equals 22.4 days (4 days x 5.6). If a full-time employee receives 28 days, a four-day-week employee on a pro-rata basis would receive 22.4 days. The calculation is the same as for any part-time worker: the statutory minimum is always expressed in weeks, and the days figure is derived from the individual's working pattern. Bank holidays are treated separately: only bank holidays that fall on the employee's working days count.
Can an employer refuse a flexible working request for a four-day week?
Yes. Employers can refuse a flexible working request on any of eight statutory business grounds: the burden of additional costs, detrimental effect on ability to meet customer demand, inability to reorganise work among existing staff, inability to recruit additional staff, detrimental impact on quality, detrimental impact on performance, insufficiency of work during the proposed hours, and planned structural changes. Employers must consider the request properly and respond within two months, giving written grounds for any refusal. The employee can appeal internally and may claim unfair dismissal if dismissed for making the request.
Is the four-day week suitable for every type of business?
No. The businesses that participated in the 2022 UK pilot were predominantly office-based, professional services and knowledge-work organisations where output is measured by results rather than hours present. A four-day week is much harder to implement in sectors where physical presence is directly tied to service delivery: retail, hospitality, healthcare, manufacturing and customer-facing roles with contracted service hours. In those sectors, a compressed week may be feasible for some roles, but a straightforward reduction in operational hours is usually not.
About this guide

Written by the Book Time Off editorial team. We build leave management software for UK SMEs and write practical guides on UK employment law, holiday entitlement, and HR best practice. All content is reviewed against current GOV.UK and ACAS guidance and updated as the rules change.

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This is not legal advice
This guide is intended to help employers understand the four-day working week debate and the relevant legal framework. It is not a substitute for legal or HR advice tailored to your specific circumstances. If you are considering a change to working patterns or responding to a flexible working request, consult ACAS (0300 123 1100) or take employment law advice for your situation.