Four Day Working Week In The UK: Legal Steps And Risks

The four day working week keeps popping up in board meetings and team chats - and for good reason.

From attracting talent to boosting focus, many SMEs are testing shorter weeks. But shifting to 4 days a week is a contractual and legal change, not just a scheduling tweak.

In this guide, we’ll explain the lawful ways to pilot or roll out a four day week in the UK, the key laws you must follow, and the contracts and policies you’ll need in place to stay protected from day one.

What Do We Mean By A Four Day Working Week?

“Four day working week” can mean different models. The most common for small employers are:

• Shorter week, same pay (typically ~32 hours) - Employees work four standard-length days (e.g. four 8-hour days) and keep the same weekly salary. This is usually the model used in high-profile pilots.
• Compressed hours (e.g. 37.5–40 hours over four days) - Staff work longer days to reach the same total weekly hours in fewer days.
• Part-time four day roles - Four days with pro-rated pay based on a reduced FTE (for example, 0.8 FTE).

Your approach affects pay, holiday accrual, overtime, scheduling, and how you amend contracts. So it’s important to pick the model that actually fits your operations and then document it properly.

Is A Four Day Working Week Legal In The UK?

Yes - but you need to implement it within the UK’s employment law framework. The main laws to consider are:

• Working Time Regulations 1998 (WTR) - Limit average weekly hours to 48 (unless a valid opt-out), set daily and weekly rest, and deal with night work. You can read a plain-English overview in our guide to the Working Time Regulations.
• National Minimum Wage Act 1998 - Ensure pay divided by total hours still meets the relevant minimum or National Living Wage.
• Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 - Part-time four day staff must not be treated less favourably than comparable full-time workers, unless objectively justified.
• Equality Act 2010 - Changes must be non-discriminatory. Allocation of the “off day,” access to overtime, and promotion opportunities all need fair, objective criteria.
• Data Protection Act 2018 and UK GDPR - If you monitor productivity, hours worked or use time-tracking tools, ensure lawful processing, transparency and minimisation.
• Health and Safety at Work etc. Act 1974 - Compressed shifts must still allow for adequate rest. Fatigue risk assessments are sensible where shifts become longer.

If you plan to compress full-time hours into four long days, pay close attention to the WTR daily and weekly rest requirements. If you’re reducing total hours (e.g. to ~32), double-check pay still meets minimum wage on an hourly basis.

Pros And Risks For Small Employers

Before you change contracts, weigh the upsides and the potential pinch points for SMEs.

Potential Benefits

• Hiring and retention - A four day week is a standout perk in job ads and can reduce churn.
• Productivity focus - Teams often streamline meetings and prioritise deep work.
• Reduced absence - An extra day for life admin can cut down on midweek appointments and short-notice leave.
• Cost optimisation - If you can stagger days off, you might reduce utilities or overtime spend.

Potential Risks

• Coverage gaps - Customer support, site visits or production may need five-day coverage or weekend peaks.
• Overtime creep - If the workload doesn’t actually shrink, staff may work fifth days anyway, risking breach or hidden costs.
• Fairness issues - If some roles can’t take a specific day off, indirect discrimination risks can arise without objective justification and a transparent process.
• Holiday and pay complexity - Bank holidays, pro-rata calculations and part-year arrangements need careful handling.

A structured pilot is often the safest path - with clear metrics, inclusion criteria, and a defined timeline.

How To Implement A Four Day Week Lawfully (Step-By-Step)

1) Decide The Model And Build Your Business Case

Pick whether you’ll reduce weekly hours with the same pay, compress hours, or move some roles to part-time. Then map how this affects client service, rota coverage, deadlines and peak periods.

Set clear success metrics (e.g. customer response times, deliverables met, overtime spend, employee engagement scores). These will help justify your approach and any changes needed after the pilot.

2) Consult Staff Early And Document Feedback

Consultation isn’t just good practice - it helps you spot operational realities and equality considerations. Keep notes of options discussed (e.g. rotating days off vs fixed patterns) and any proposed mitigations for roles with less flexibility.

3) Plan A Time-Limited Pilot With Clear Rules

Most SMEs start with a 8–16 week pilot. Define who’s in scope, how you’ll handle urgent fifth-day work, what counts as overtime, and how exceptions are approved. Publish the criteria to promote fairness and transparency.

4) Amend Contracts And Policies

A four day week is usually a change to terms and conditions. For existing staff, follow a proper process for changing employment contracts - consult, seek consent, and confirm changes in writing. If you’re recruiting into the new pattern, issue an Employment Contract that sets out the hours model from day one.

Update your Staff Handbook and any relevant Workplace Policy so your overtime, holiday, flexible working and timekeeping rules align with the new approach.

5) Check Compliance With Working Time And Pay

Confirm that employees’ total hours remain within the WTR or that valid opt-outs are in place where needed. Ensure the average hourly pay still meets National Minimum Wage/National Living Wage thresholds.

If staff occasionally work a fifth day, be clear when that is authorised and whether it will be paid as overtime or time off in lieu (TOIL).

6) Train Managers And Communicate The Rules

Managers need to apply the same rules consistently, particularly for approving exceptions, managing workload on compressed days and handling customer escalations. Explain the “why” to the team, the guardrails for the pilot, and how you’ll measure success.

7) Monitor, Review And Decide

Collect data on output, client experience, overtime, wellbeing, and any equality impacts. If the pilot works, confirm the change and issue formal variation letters. If it needs tweaking (e.g. rotating days off or adjusting coverage), consult again before finalising.

Key Legal Issues When Moving To Four Days

Working Time: Hours, Rest And Opt-Outs

If you compress hours into four long days, make sure you still provide 11 hours’ daily rest and 24 hours’ weekly rest (or 48 hours’ rest every 14 days). Night workers and young workers have additional protections. For a refresher on average weekly limits, rest breaks and opt-outs, see the Working Time Regulations.

Minimum Wage And Salary Calculations

When you reduce hours with no change to salary, your hourly rate increases - usually fine. But if you compress hours, check the implied hourly rate still meets National Minimum Wage/National Living Wage, especially for junior roles or apprentices.

Holiday Entitlement And Bank Holidays

Statutory minimum holiday is 5.6 weeks. For a four day full-time pattern, that’s 22.4 days (5.6 × 4). If you close on bank holidays, decide whether they come out of this allowance or sit on top, and explain the approach in contracts and policies. For part-time arrangements, pro-rate entitlement carefully and keep a clean record.

Part-Time And Fair Treatment

If some team members move to four days as part-time, the Part-time Workers Regulations mean they should get comparable pay, bonuses and benefits on a pro-rata basis, unless a different approach can be objectively justified. Our plain-English guide to part-time employment explains the basics.

Equality And Allocation Of The “Off Day”

Be cautious about fixed Fridays if that disadvantages certain groups (for example, religious observance or caring responsibilities). Offer alternatives or rotations where feasible and document objective reasons for any constraints (such as client contracts or production schedules). Train managers to apply criteria consistently.

Monitoring Hours And Productivity

If you track activity (e.g. time-tracking apps or biometric access), ensure you have a lawful basis under UK GDPR, keep data to a minimum, and explain monitoring in your privacy notices and policies. If you use biometrics for clocking in, follow strict data protection safeguards.

Contracts, Policies And Documents You’ll Likely Need

Getting your paperwork right makes your four day week workable and enforceable. At a minimum, consider:

• Employment Contract - Hours of work model (compressed vs reduced), place of work/remote rules, pay, overtime/TOIL, and how rota changes are agreed. New starters should receive an up-to-date Employment Contract reflecting the four day week.
• Contract Variation Letters - For existing staff, confirm pilot terms and any permanent changes in writing, with start dates and review points.
• Staff Handbook - Align your holiday rules, scheduling, overtime/TOIL, flexible working and timekeeping. A clear Staff Handbook keeps day-to-day decisions consistent.
• Working Time Records - Keep records to show compliance with WTR, including opt-outs where used.
• Overtime/TOIL Policy - Define when fifth-day work is authorised, approval workflows, and rates or TOIL conversion.
• Equality Impact Note - Useful to document how you’ve assessed and mitigated discrimination risks when allocating days off.
• Data Protection Documentation - Update privacy notices and policies if new monitoring or time-tracking tools are introduced.

Avoid generic templates for these - they need to reflect your actual pattern, industry hours and customer commitments. Getting the core documents professionally drafted reduces disputes later.

Managing Pay, Holiday And Overtime In A Four Day Week

Defining Full-Time Equivalent (FTE)

Decide what “full-time” means in your business post-change. If 32 hours is your new full-time, define and communicate it. Then set pro-rata calculations for four day part-time roles and any three day roles.

Holiday Accrual And Requests

For four day full-time roles, adjust holiday entitlement to 22.4 days (or your enhanced amount). For part-time, calculate entitlement in days or hours to avoid confusion when staff take time off on longer compressed days. Make sure your policy covers bank holidays fairly (e.g. pro-rated allowance for part-time colleagues so they aren’t disadvantaged).

Overtime And TOIL

Spell out what counts as out-of-hours work and which manager can authorise it. Confirm whether overtime is paid, paid at a premium, or converted to TOIL. For practical guidance on common pitfalls and options, see our overview of overtime.

Zero-Hour And Contractors

If you rely on zero-hour staff to plug coverage gaps, keep an eye on evolving reforms and ensure the status really is casual or worker rather than employee. Mislabelling status can create liabilities for holiday pay and unfair dismissal. If you’re uncertain about status, review the practical differences between a worker and an employee before you scale hiring.

Fair Process For Existing Staff

Changing hours is usually a contractual variation. To reduce legal risk and keep morale high:

• Consult meaningfully - Explain the business rationale, invite feedback, consider alternatives for roles with less flexibility.
• Seek written consent - For permanent changes to terms, follow a clear process for changing employment contracts and record agreement.
• Use pilots wisely - Time-limit the pilot, set measurable criteria, and confirm the final outcome in writing (adopt, adjust, or revert).
• Keep performance fair - If performance dips, use your normal process (e.g. objectives, support, and - if needed - a structured plan) rather than abandoning the model prematurely.

If you do need to address individual underperformance in a four day context, ensure objectives and measures are role-appropriate and attainable within the new pattern before jumping to formal steps like a Performance Improvement Plan.

Operational Tips That Make A Four Day Week Work

• Stagger days off - Use rota patterns to keep phones, inboxes and delivery windows covered five days a week (or seven, if that’s your model).
• Streamline meetings - Protect focus time and avoid scheduling recurring meetings on the popular “off day.”
• Service-level guardrails - Publish internal targets (response times, order cut-offs) so everyone knows what “good” looks like in four days.
• Timekeeping clarity - If you introduce new tools or stricter time logs, be transparent and respectful of privacy. If considering biometrics, revisit the data protection points and safeguards for clocking in.
• Onboarding - Ensure new joiners’ Employment Contract and induction materials explain the working pattern, overtime/TOIL, and holiday rules clearly.

Common FAQs From Small Employers

Do We Need Written Opt-Outs If Staff Sometimes Work A Fifth Day?

An occasional extra day doesn’t automatically trigger a WTR breach, because the 48-hour limit is an average over a 17-week reference period. But if your pattern means some staff will regularly exceed 48 hours when compressed, you’ll want individual opt-out agreements and robust rest breaks.

Can We Pay The Same Salary For Fewer Hours?

Yes - many four day week pilots follow a 100:80:100 model (100% pay, 80% time, 100% output). Ensure minimum wage thresholds are still satisfied and be clear about performance expectations and deliverables.

Do Part-Time Four Day Staff Get Fewer Bank Holidays?

Bank holidays should be managed fairly. A common approach is giving part-time staff a pro-rated bank holiday entitlement in hours, then deducting from that pot when a bank holiday falls on their usual working day.

Can We Run The Four Day Week Only For Certain Teams?

Yes, if there’s a sound business reason, but be mindful of equality risks. Apply objective criteria, document your rationale, and consider compensating benefits (e.g. flexible start/finish times) where some roles can’t take the reduced week.

Key Takeaways

• A four day working week is lawful in the UK, but you must comply with Working Time Regulations, minimum wage rules, equality law and data protection requirements.
• Choose your model first (reduced hours vs compressed hours vs part-time) - it drives how you calculate pay, holiday and overtime, and how you amend contracts.
• Consult your team, run a time-limited pilot with clear metrics, and confirm any permanent change in writing using contract variations or an updated Employment Contract.
• Update your Staff Handbook, timekeeping and overtime rules so day-to-day decisions are consistent and enforceable.
• For part-time four day roles, ensure fair pro-rata treatment under the Part-time Workers Regulations and set clear holiday rules (including bank holidays).
• If you monitor hours or productivity, be transparent and follow UK GDPR - especially if you use biometric or other intrusive tools for clocking in.
• When in doubt, get tailored advice before making contractual changes - handling legals properly now prevents disputes, grievances and costly reworks later.

If you’d like help designing a compliant four day week pilot, updating your contracts and policies, or sense-checking your calculations, you can reach us on 08081347754 or team@sprintlaw.co.uk for a free, no-obligations chat.