When does overtime have to be included in holiday pay?
Holiday pay must be calculated on the basis of the employee's normal pay. Where an employee normally works overtime, this should be included in the calculation of their holiday pay.
Overtime that the employer is contractually obliged to offer and that employees are required to work must always be included in holiday pay. In Bear Scotland Ltd and others v Fulton and others; Hertel (UK) Ltd v Woods and others; Amec Group Ltd v Law and others  IRLR 15 EAT, the Employment Appeal Tribunal (EAT) held that regular overtime that is not guaranteed, but that employees are required to work when it is offered, must also be included.
There is no definition setting out how regularly overtime must be worked for it to be included, but the general principle is that pay that is "normally received" should be included in holiday pay. If an employee has worked a settled pattern of overtime over a period of time, payment for that overtime is pay that they normally receive and must therefore be included in holiday pay. Where there is no settled pattern of overtime, the employer should calculate average pay over a reference period leading up to the period of annual leave, although the courts have not addressed what a suitable reference period would be.
The Court of Appeal addressed the question of whether or not overtime that is voluntary must be included in the calculation of holiday pay in East of England Ambulance Service NHS Trust v Flowers and others  IRLR 798 CA. It held that voluntary overtime must be included if it is part of a pattern of work that is sufficiently regular and settled for payments made in respect of it to amount to normal remuneration. This will be for tribunals to decide on the facts of each case.
The right to be paid for non-guaranteed overtime in holiday pay derives from case law of the European Court of Justice, and so applies only to holiday pay for the four weeks' minimum annual leave under EU law, not to the additional 1.6 weeks provided for by the Working Time Regulations 1998 (SI 1998/1833). Employers should decide their policy on how to treat the additional 1.6 weeks' statutory minimum leave and any additional contractual entitlement, but may decide to include pay for overtime in all holiday pay to avoid complicating the administration of payments.