‘Pay intervals’ are the periods of time in between payments you receive, usually a week or a month. The odd day or days at the end of the last complete tax week are added up to make a full week – known as week 53.
If you work for an umbrella company, then they will pay you regularly, generally weekly or monthly. The duration between these payments is known as a ‘pay interval’. These weeks typically follow ‘tax weeks’, periods of 7 days which follow on from each other starting on 6 April each year. So the first tax week runs from 6 to 12 April inclusive, the second tax week runs from 13 to 19 April inclusive, and so on.
This system allows all payroll systems to track time in the same way, but it means that an odd day or days may accrue at the end of the last complete tax week in the year, (5 April or in leap years, 4 and 5 April). To solve this, they are treated as a whole tax week, which is referred to as ‘week 53’. Payments made in week 53 are made on a non-cumulative basis. This means they may lead to an underpayment, due to the extra personal allowance provided to protect the level of take home pay in that pay period.