Tax month and tax week

Tax months of 2026 to 2027

Every tax month starts on the 6th, which is why the payslip for pay received on the 28th of a month carries the number of the tax month that began on the 6th of that same month. The table gives the dates for the current year and the free pay to date that a cumulative 1257L reaches by each month. For month 1 that is the same £1,048.26 you see quoted as the monthly figure; by month 12 it adds up to slightly more than the yearly £12,570, because HMRC's tables round the free pay for each code up.

A pay day close to a boundary needs care. An employer who pays on the 5th puts each payment in the tax month that is ending, so the April pay of someone paid on 5 May is month 1 and the pay on 5 April closes month 12. An employer who pays on the 6th or later starts the new month with it.

Tax weeks and week 53

Weekly payroll counts tax weeks from 6 April in blocks of seven days, whatever weekday that is. Week 1 of 2026 to 2027 runs from 6 April 2026 to 12 April 2026, and each later week starts seven days after the one before. With a cumulative code, the week number multiplies the weekly free pay of £241.92 for 1257L.

Fifty-two weeks of seven days cover 364 days, so one day is left over, or two in a leap year. In 2026 to 2027 that day is 5 April 2027, a Monday: someone paid weekly on Mondays receives a pay in week 53. HMRC's payroll specification does not give that pay a fifty-third week of free pay; it taxes it on a non-cumulative basis with the week 1 tables. Fortnightly and four-weekly payrolls have the same issue, which the specification handles as weeks 54 and 56 with the week 2 and week 4 tables. BR, D and NT codes need nothing special in those weeks apart from the non-cumulative basis.

Why the period number changes your tax

On a cumulative code, payroll compares your pay to date with the free pay for the current period number, so a wrong number would give the wrong allowance. If you start a job in tax month 7 after months without work, payroll still uses period 7 and gives you seven months of free pay at once, which is why the first payslip can show little or no tax. The page on how PAYE is calculated walks through that example in full, and the payslip calculator takes the tax month as an input.

On a week 1 or month 1 code, by contrast, the period number has no effect: every pay gets one week's or one month's free pay. That is why an emergency code costs most to someone who starts late in the year. At the turn of the year, the count restarts at 1 on 6 April, and HMRC's P9X instructions tell employers to drop any week 1 or month 1 marking from the code carried into the new year.