Archive Website of the UK government

The basic calculation

To know 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 or collective agreement you can agree with your employer to calculate the average weekly working time over a different period, anything up to 52 weeks. These are agreements that have been reached between an employer and a trade union. Your contract of employment will probably set out which collective agreements cover you.

Some careers automatically have a different reference period:

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

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 (normally 17 weeks).

For example:

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

Step 1: multiple your standard working hours by the number of weeks in the pay reference period (17 weeks x 40 hours = 680 hours)

Step 2: add on your overtime (12 hours x 10 weeks = 120 hours overtime + 680 hours = 800 hours)

Step 3: the total hours should be divided by the number of weeks in the pay reference period (800 hours ÷ 17 weeks = 47.1 hours)

So you would have worked an average of 47.1 hours per week, which is 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:

• paid annual leave - up to the first four weeks of your statutory paid annual leave entitlement
  
• maternity leave
• paternity leave
• adoption leave
• parental leave
• time off sick

You do this by extending the reference period by the same number of days as you were away. You also look at the hours you worked on the days which were immediately before the 17-week period.

For example:

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 1: add together the 16 weeks of normal hours and one other normal work day (40 hours x 16 weeks = 640 hours + 8 hours = 648 hours)

Step 2: work out your overtime hours (8 hours x 12 weeks = 96 hours)

Step 3: add together your total normal hours plus your overtime in the pay reference period (648 hours + 96 hours = 744 hours during your pay reference period)

Step 4: include the time you worked on the four days directly after the 17 week pay reference period (4 days x 8 hours = 32 hours + 744 hours = 776 hours)

Step 5: the total hours should be divided by the number of weeks in the reference period (776 hours ÷ 17 weeks = 45.6 hours)

So you would have worked an average of 45.6 hours per week, which is within the working time limits.

Calculating working time with shift patterns

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

For example:

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 1: 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 2: 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 3: minus one day a week as a legal rest day (119 – 17 = 102 work days in the reference period)

Step 4: calculate you weekly average by dividing the hours you worked by the number of days (816 hours ÷ 102 days = 8 hours a day)

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

Where to get help

If you need further help the Pay and Work Rights helpline offers free and confidential advice on working hours.

• Pay and Work Rights Helpline