How to Calculate Working Hours Correctly Under UK Rules

If you only want the arithmetic done, use the working hours calculator: it totals a week of start times, end times and breaks and gives you decimal hours for payroll. This page is about the rules behind the numbers, which is where UK employers actually get caught out.

What counts as working time

The Working Time Regulations 1998 define working time as any period when a worker is working, at the employer's disposal and carrying out their duties. Three consequences that surprise people:

• Travel between assignments counts. For a mobile worker with no fixed base, travel from home to the first job and from the last job home is working time.
• On-call at the workplace counts, even when the worker is asleep, if they are required to be there.
• Unpaid overtime still counts for working time and average pay purposes, even where the contract says otherwise.

Working time and paid time are not the same test. A period can count towards the 48-hour average or the minimum wage calculation while not being contractually paid at the overtime rate.

Breaks: what you deduct and what you do not

• Workers over 18 are entitled to an uninterrupted 20-minute rest break when the working day exceeds six hours.
• The break must be during the shift, not at the start or end, and workers must be free to leave their workstation.
• Rest breaks are unpaid unless the contract says otherwise, so they come out of paid hours.
• A break where the worker must stay at their post, answer the phone or cover reception is not a rest break, and that time remains working time.
• Young workers under 18 get 30 minutes where the day exceeds 4.5 hours.

If you deduct 30 minutes automatically every day but staff routinely work through lunch, you are under-recording hours and, at low pay rates, risking a minimum wage breach.

The calculation, step by step

For each day: end time minus start time, minus qualifying unpaid breaks. Convert to decimal for payroll rather than working in hours and minutes.

• Divide the minutes by 60. Nine hours fifteen minutes is 9.25, not 9.15. This one error, repeated weekly, is a common payroll discrepancy.
• Round consistently or not at all. Rounding down every shift to the nearest 15 minutes systematically underpays and is not defensible.
• Total the week, then compare against contracted hours to identify overtime.

Worked example: 08:30 to 17:15 with a 30-minute unpaid break is 8 hours 15 minutes, or 8.25 decimal hours. Five such days is 41.25 hours, so 1.25 hours of overtime against a 40-hour contract.

The 48-hour average

The weekly limit is an average of 48 hours over a 17-week reference period, not a hard cap on any single week. Add total hours across the reference period and divide by the number of weeks, excluding annual leave and sickness and replacing those days with hours from the following period.

Workers can opt out in writing individually. An opt-out cannot be imposed through the handbook or as a condition of the job, and the worker can withdraw it with up to three months' notice. Certain sectors, including drivers under separate rules, cannot opt out.

Records you are required to keep

• Adequate records showing compliance with the 48-hour limit, kept for two years.
• Minimum wage records, kept for six years, sufficient to show each worker was paid at least the applicable rate for their hours.
• For salaried staff, hours worked still matter: a salary that divides below the minimum wage once actual hours are counted is a breach regardless of what the contract states.

Where hours vary, holiday pay is calculated on average weekly pay over the previous 52 paid weeks, so your hours records feed directly into holiday pay accuracy.

Common ways employers get this wrong

• Deducting breaks that were never taken.
• Treating unpaid overtime as invisible for working time and minimum wage.
• Rounding in the employer's favour every time.
• Using hours-and-minutes arithmetic in a spreadsheet built for decimals.
• No records at all for salaried staff near the minimum wage.
• Ignoring travel time for mobile workers.

If any of those are happening across a workforce rather than one payslip, the fix is a system rather than a spreadsheet. See the guidance on HR software, or find a provider in your city through the directory. For holiday, the holiday entitlement calculator handles the pro rata arithmetic.

Sources

• Working Time Regulations 1998, on working time, rest breaks and the 48-hour average.
• Gov.uk guidance on maximum weekly working hours and the opt-out.
• Gov.uk and HMRC guidance on National Minimum Wage record-keeping.