Calculating your working time (2024)

Your employer cannot make you work longer than an average of 48 hours a week. If you do work longer, you should discuss reducing your hours with your manager or signing an opt-out agreement.

Working out the basic calculation

To work out how long you are working, you need to calculate the number of hours you work each week (including overtime) and then average these hours over a set period.

Your average working hours are calculated over a ‘reference period’, which is normally a 17-week period. You can work more than 48 hours in one week, as long as the average over 17 weeks is less than 48 hours per week.

Changing the average working time reference period

With a workforce agreement (or a collective agreement that has been reached between an employer and a trade union) you can agree with your employer to calculate the average weekly working time over a different period, which could be anything up to 52 weeks. Some careers have a different reference period:

doctors in training have a 26-week reference period
the offshore sector has a 52-week reference period

Your contract of employment will probably set out which collective agreements cover you.

Calculating your average weekly working time

To calculate your average weekly working time you should add up the number of hours you worked in the reference period. Then divide that figure by the number of weeks in the reference period which is normally 17 weeks.

Example one

You have a standard working week of 40 hours (eight hours a day). You also do 12 hours overtime a week for the first 10 weeks of your 17-week reference period.

step one: 17 weeks of 40 hours and 10 weeks of 12 hours overtime (17 x 40) + (10 x 12) = 800
step two: 800 hours should be divided by 17 (the number of weeks in the reference period) 800 ÷ 17 = 47.1

So you would have worked an average of 47.1 hours per week. This would be within the working time limits.

Calculating working time when you have taken leave

You will need to make up time in your calculation if you are away during the reference period because you are taking:

Example two

You have a standard working week of 40 hours (eight hours a day). You then do overtime of eight hours a week for the first 12 weeks of your 17-week reference period. You also take four days annual leave and work one normal day (eight hours) that week. When you return to work, you only do your normal hours with no overtime for one week.

step one: add together the 16 weeks of normal hours, plus one day normal hours, plus the 12 weeks of overtime (16 x 40) + (1 x 8) + (12 x 8) = 744 hours during the reference period
step two: include the time worked on the four days directly after the 17-week period 4 x 8 = 32 + 744 = 776
step three: 776 hours should be divided by 17 (the number of weeks in the reference period) 776 ÷ 17 = 45.6

This means you would have worked an average of 45.6 hours per week, which would be within the working time limits.

Calculating working time with shift patterns

If you work shifts, you will need to use the following formula to work out your average working time.

Example three

You are a night worker and you normally work four 12-hour shifts each week. The total number of normal hours of work for a 17-week reference period is:

step one: calculate the number of hours you have worked: 17 weeks of four shifts of 12 hours: 4 x 12 = 48 hours x 17 = 816 hours
step two: work out the number of days you could have been asked to work: 17 weeks x 7 days = 119 days in the reference period
step three: take away one day a week as a legal rest day: 119 – 17 = 102 work days in the reference period
step four: calculate your weekly average by dividing the hours you worked by the number of days: 816 hours ÷ 102 days = eight hours a day

This means that you would work an average of 48 hours a week, which is within the working times limits.

Where to get help

For more information on where to get help with employment issues, contact your trade union.

Introduction to trade unions