Software that allocates shifts, ranks performance or sets bonuses often works on raw totals: hours logged, tasks completed, sales made. Someone on fewer hours can end up behind on every measure simply because they work less, and then miss out on overtime, training slots or a bonus. In Great Britain the Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 give part-time workers a right not to be treated less favourably than comparable full-time workers. They apply to workers, not only employees.
The short answer: an employer must not treat a part-time worker less favourably than a comparable full-time worker, as regards contract terms or by any other detriment, on the ground that they are part time, unless the treatment is justified on objective grounds (reg 5). Pay and benefits are compared pro rata. A worker can ask for written reasons, which the employer must give within 21 days (reg 6), and can complain to an employment tribunal (reg 8).
Who counts as part time, and who to compare with
A worker is part time if they are paid wholly or partly by reference to the time they work and, having regard to the employer's custom and practice for workers on the same type of contract, are not identifiable as a full-time worker (reg 2(2)). There is no fixed number of hours.
The claim needs a comparable full-time worker: someone employed by the same employer under the same type of contract, engaged in the same or broadly similar work (having regard, where relevant, to similar qualifications, skills and experience), who works or is based at the same establishment. Only if there is no such person there can a comparator at a different establishment be used (reg 2(4)). Employees, apprentices and workers who are not employees count as different types of contract (reg 2(3)).
The right not to be treated less favourably
The right covers the terms of the contract and any other detriment by an act, or deliberate failure to act, of the employer (reg 5(1)). It applies only if the treatment is on the ground that the worker is part time and is not justified on objective grounds (reg 5(2)). So the question with an automated system is why it produced the result: a rule that ranks people on total output, without adjusting for hours, may disadvantage part-timers because of their hours. Whether that is unlawful in a given case depends on the facts and on any objective justification the employer shows.
The pro rata principle
Where a comparable full-time worker receives pay or any other benefit, the part-time worker is to receive not less than the proportion of it that their weekly hours bear to the full-timer's weekly hours (reg 1(2)). This principle is applied in deciding whether treatment was less favourable, unless it is inappropriate (reg 5(3)). For example, a bonus pool or a performance target set for full-time hours can be checked against it.
There is one specific exception for overtime: paying a part-timer a lower overtime rate is not less favourable treatment for that reason so long as their total hours in the period, including overtime, do not exceed the full-timer's contractual hours for the period (reg 5(4)).
Asking for written reasons
A worker who considers their employer may have infringed the right can ask in writing for a written statement of the reasons for the treatment, and is entitled to it within twenty-one days of the request (reg 6(1)). The statement is admissible as evidence. If the employer deliberately and without reasonable excuse fails to provide one, or gives one that is evasive or equivocal, the tribunal may draw any inference it considers just and equitable, including that the right was infringed (reg 6(3)). This does not apply to a dismissal where the employee is entitled to written reasons under section 92 of the Employment Rights Act 1996 (reg 6(4)).
A reply that only says "the system decided" gives the worker little to go on. Employers using scoring or rota software should be able to explain which inputs drove a result.
Protection for using these rights
A worker must not be subjected to a detriment, and an employee is regarded as unfairly dismissed, where the reason is that they brought proceedings, asked for written reasons, gave evidence, alleged an infringement, or refused to give up a right under the Regulations (reg 7). This does not apply to an allegation that is false and not made in good faith (reg 7(4)).
Making a claim
A worker can complain to an employment tribunal (reg 8(1)). The complaint must be presented within six months of the less favourable treatment or detriment, or the last of a series of similar acts, with an extension for Acas early conciliation; the tribunal may hear a late claim if it is just and equitable to do so (reg 8(2) to (3)). The six-month period was substituted from 1 October 2026 by SI 2026/758, which has transitional provisions, so check which period applies to treatment before that date. Where a contract term is less favourable, the treatment is treated as taking place on each day the term applies (reg 8(4)(a)). It is for the employer to identify the ground for the treatment (reg 8(6)).
If the complaint succeeds, the tribunal can make a declaration, order compensation and recommend action to reduce the adverse effect (reg 8(7)). Compensation is what is just and equitable, including expenses and lost benefits, and for a breach of regulation 5 it does not include injury to feelings (reg 8(9) to (11)).
Practical steps
- Employers: before using totals of output, sales or hours to allocate shifts, training, overtime or bonuses, check how the rule treats people on fewer hours, and adjust targets and pools pro rata where that is appropriate. Record the objective reason for any rule that still leaves part-timers worse off. Be ready to answer a written request within 21 days with the real reasons.
- Workers: identify a full-time colleague on the same type of contract doing broadly similar work. Compare pay, bonus and benefits pro rata. If you think you were treated worse because you work part time, ask in writing for the reasons and keep a copy. Note the time limit. For rota rules generally, see UK rules on software-set rotas; to ask for different hours, see flexible working requests. If you are also on a fixed-term contract, see fixed-term employees' rights.
These Regulations extend to England, Wales and Scotland; Northern Ireland has separate legislation. This page is general information on the law in Great Britain as at 1 November 2026, not legal advice.
Questions and answers
Can my employer treat me worse because I work part time?
Not as regards contract terms or by any other detriment on the ground that you are part time, unless the treatment is justified on objective grounds (Part-time Workers Regulations 2000, reg 5).
Who do I compare myself with?
A full-time worker employed by the same employer on the same type of contract, doing the same or broadly similar work, at the same establishment, or at another establishment if there is no one suitable at yours (reg 2(4)).
What is the pro rata principle?
A part-time worker should receive at least the proportion of a comparable full-timer's pay or benefit that their weekly hours bear to the full-timer's weekly hours (reg 1(2)), unless applying it is inappropriate (reg 5(3)).
Can I ask why I was treated differently?
Yes. Ask in writing and the employer must give a written statement of reasons within 21 days (reg 6(1)).
How long do I have to claim?
Six months from the treatment or the last of a series, with an extension for early conciliation; the tribunal can allow a late claim where just and equitable (reg 8).