How Does a 4 Day Week Work? Effects on Employment Contracts and Employee Rights in the UK

Imagine working four days a week but still getting paid for five. Sound too good to be true? The 4 day working week is no longer just a buzzword or experimental pilot - it’s fast becoming a real option for many UK businesses looking to boost staff wellbeing, productivity, and recruitment. But switching to a shorter workweek isn’t as simple as locking the office for an extra day. If you're an employer or employee considering this shift, it’s crucial to understand how a 4 day week works in practice, what happens to employment contracts, and which rights are affected. Keep reading to ensure your legal foundations are set strong from day one.

What Is a 4 Day Working Week and How Does It Work?

The “4 day week” means reducing the standard workweek from five days to four, usually without a pay cut or loss of employee benefits. This approach, often referred to as the “100-80-100” model, means employees receive 100% of their pay while working 80% of the time, in return for a commitment to maintain 100% productivity.

This model can be structured in various ways:

• Compressed hours: Employees complete their full weekly hours over four longer days.
• Reduced hours with no pay cut: Staff work fewer total hours for the same pay.
• Rotational days off: Teams stagger their non-working days to maintain coverage.

However you structure it, there are important legal and contractual considerations to address before making a change.

Why Are Employers Considering a 4 Day Work Week?

Driven by pilot programmes and media headlines, the 4 day working week is building steam across the UK. Employers are increasingly interested due to:

• Staff demand for better work-life balance
• Productivity boosts reported by early adopters
• Improved employee retention and easier recruitment
• Potential savings on utilities and overheads

The challenges? Adapting workflows, maintaining service levels, and - most importantly - navigating the legal impacts on contracts and staff rights.

How Does a 4 Day Week Affect Employment Contracts?

Transitioning to a four-day week is a contractual change. Put simply: you can’t just tell staff to stop coming in on Fridays without updating their contract terms.

Key considerations include:

• Working hours: You’ll need to specify new weekly hours and usual working days.
• Pay: Will pay remain unchanged? This is vital to clarify in the contract.
• Holiday/leave entitlement: Annual leave needs recalculating to match the new pattern.
• Overtime or TOIL: Clarify what counts as “extra hours” under the new regime.
• Flexibility clauses: Check if current contracts already allow for changes, or if employee consent is required.

In most cases, you’ll need to follow the legal process for changing employment contracts in the UK, including proper consultation and (where needed) individual written agreement from each staff member.

Do You Need Employee Consent for a 4 Day Work Week?

Yes, you almost always need staff buy-in for such a significant change. Unless your contracts have explicit “flexibility clauses” granting management the right to change working hours unilaterally, you’ll need to obtain each employee’s agreement. Imposing a 4 day week without consent risks breach of contract and potential claims for constructive dismissal.

The safest path is to consult with staff openly, explaining:

• What you want to change (and why)
• How pay and benefits will be protected (where relevant)
• Any trial periods or opportunities for feedback
• How contract terms will be formally updated in writing

A template for this kind of contract change can be found in our Essential Guide to Contract Modification.

How Should Employers Update Contracts for a 4 Day Week?

To ensure you’re protected from disputes, it’s crucial to update employment contracts clearly. This includes:

• Revising the “Working Hours” clause to describe the new days/times and expectation of attendance.
• Setting out the “Pay” arrangements, clarifying that salary will not decrease (if applicable).
• Updating the “Annual Leave” clause - e.g., if holiday entitlement is expressed in days, consider whether staff now need fewer days to get the same leave length as before.
• Amending any clauses mentioning “full-time” or “part-time” to reflect the new definition of full time in your organisation.
• Clarifying how overtime is calculated given the new working pattern.

It’s smart to formally amend contracts with an addendum or a new employment contract letter, signed by both parties. Avoid unclear, informal agreements - they rarely hold up in disputes.

How Are Employee Rights Affected by a 4 Day Working Week?

Switching to a 4 day week affects several core employee rights and entitlements. Here are the big ones to review:

1. Statutory Paid Leave (Holiday Entitlement)

The UK statutory minimum holiday is 5.6 weeks per year (usually calculated as 28 days for full-time staff). Moving to a 4 day workweek means you need to recalculate leave in “weeks” instead of “days” - for instance, entitlement would typically become 22.4 days per year (5.6 x 4).

For more guidance, check our article on calculating holiday entitlement.

2. Sick Pay and Other Leave

Sick pay, parental leave, and compassionate leave should remain proportionally equivalent to what employees received on five days - the key is ensuring staff aren’t unfairly disadvantaged by the change in work pattern. Any policy change should be set out in your staff handbook or employment contracts.

3. National Minimum Wage Compliance

When reducing total working hours but keeping pay the same, National Minimum Wage (NMW) compliance usually isn’t affected (in fact, effective hourly rates may increase). But if you’re adjusting pay or moving to compressed hours, double-check NMW calculations.

Learn more in our Minimum Wage Guide.

4. Working Time Regulations

The Working Time Regulations 1998 govern maximum weekly working hours, rest periods, and breaks:

• Normally, staff can’t be required to work more than 48 hours a week (unless they opt out).
• Employees are entitled to at least 11 consecutive hours’ rest in each 24-hour period, and at least one full rest day each week.
• Daily rest breaks (e.g., for lunch) must still be honoured.

If your 4 day model uses compressed hours, ensure these rules aren’t breached.

You can review the details in our Working Time Regulations Guide.

5. Discrimination and Flexible Working

Changing work patterns must be fair and free from discrimination. For example, if you offer a 4 day week to some roles but not others, you must justify the business need. Staff can make statutory requests for flexible working, so be ready to handle requests for different shift patterns, or for reverting to a 5 day week on grounds such as childcare or disability.

Our article on flexible working reforms explains best practices for UK employers.

What Legal Steps Should Employers Follow When Moving to Four Days?

Here’s a step-by-step summary to ensure your transition is legally compliant:

1. Consult with Employees: Share your proposal and listen to concerns. Consider a trial period.
2. Seek Consent: Obtain written agreement to contractual changes.
3. Update Contracts: Formally revise contracts and staff handbooks to reflect the new arrangement.
4. Recalculate Entitlements: Adjust holiday, sick leave, and other benefits appropriately.
5. Maintain Compliance: Ensure policies adhere to employment law - especially Working Time Regulations, discrimination law, and minimum wage rules.
6. Communicate Changes Clearly: Give staff easy access to updated policies and offer open feedback channels during any trial.

It’s smart to get employment law advice before implementing major changes - our guide to staff contracts covers best practices for staying compliant.

What If Employees Don’t Agree to a 4 Day Week?

If some employees don’t consent, you must decide whether to:

• Keep them on their existing terms
• Negotiate individually to reach agreement
• As a last resort, terminate their contract and re-engage on new terms (a risky approach open to unfair dismissal claims if not handled lawfully)

Compulsory changes can lead to low morale, legal claims, or even staff leaving - so prioritise open communication and seek legal help if you’re unsure.

How Does a 4 Day Week Affect Existing Part-Time, Flexible or Zero-Hour Contracts?

A four-day week may have knock-on effects on other working patterns:

• Part-time staff: Adjust hours to maintain fairness - review whether their pay or entitlement needs to change.
• Flexible/remote workers: Ensure contract changes apply fairly and don’t inadvertently discriminate.
• Zero-hour contracts: If you rely on variable shifts or casual workers, clarify how shift allocation will work on a shorter week. See our zero-hour contracts guide for details.

Consistency is essential to avoid indirect discrimination or confusion among the workforce.

Common Mistakes and Legal Risks to Avoid When Introducing a 4 Day Work Week

Making the change is a big win for many organisations - but there are easy pitfalls for employers to avoid:

• Forgetting to update contracts formally (verbal arrangements rarely protect you)
• Failing to properly adjust holiday calculations
• Applying changes inconsistently between staff or teams
• Imposing the new schedule without adequate consultation or consent
• Ignoring the impact on other policies, like overtime and flexible working
• Leaving yourself exposed to claims of breach of contract, discrimination or unfair dismissal

Sound daunting? Don’t worry - with the right support and a step-by-step approach, you’ll keep your team and business protected.

Key Takeaways: The 4 Day Working Week and Employment Law

• Switching to a 4 day week is a significant contractual change that usually requires employee consent.
• Employment contracts must be updated to define new hours, pay, holidays, and overtime rules.
• Statutory rights such as annual leave, sick pay, and minimum wage need recalculating to match the new schedule.
• Consult with staff openly, use written agreements, and communicate changes clearly to avoid legal disputes.
• Apply changes fairly to avoid claims of discrimination, especially with part-time and flexible workers.
• Always seek legal advice before amending contracts or implementing major policy changes - this will protect your business and your team.

If you’re planning to introduce a 4 day week, or have questions about updating employment contracts and staff rights in your business, we’re here to help. You can reach us at team@sprintlaw.co.uk or call 08081347754 for a free, no-obligations chat with one of our friendly legal experts. Set up the right legal foundations - and make your move to a 4 day week work for everyone.